Osteology of Orodromeus makelai and the phylogeny of basal ornithopod dinosaurs by Rodney Dwayne Scheetz A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biological Sciences Montana State University © Copyright by Rodney Dwayne Scheetz (1999) Abstract: The small Upper Cretaceous ornithopod dinosaur Orodromeus makelai, possesses many tooth traits reminiscent of Triassic fabrosaurs. Determining whether these teeth were retained from a primitive lineage or independently derived within Orodromeus prompted a critical examination and ultimate revision of hypsilophodontid and basal ornithopod phytogeny. The revision of the Hypsilophodontidae resulted in a dissolution of the group into a pectinate grade of dinosaurs with a concommitment trend in increased size and herbivorous efficiency. Phylogenetic context reveals Orodromeus as nested within ornithopods with established herbivorous adaptations. Anomalous triangular teeth and high angle occlusion in Orodromeus is thought indicative of a shift to insectivory, possibly retained from the neonate condition. Other juvenile conditions, such as large orbits and unfused elements in mature specimens, together with rapid deacceleration of radial femoral bone growth through ontogeny is suggestive of neoteny. Continued histological studies of fossil taxa, together with a clear understanding of relationships, would help to identify heterochronic shifts in evolution. Analysis of 20 taxa, using 124 morphological characters, indicates the pandemic distribution of small ornithopod taxa occurred prior to the Upper Jurassic. Although hadrosaurs diversified in the Upper Cretaceous as did angiosperms, most all major herbivorous adaptations were in place within ornithopods prior to the first occurrence of angiosperms in North America.  OSTEOLOGY OF ORODROMEUS MAKELAI AND THE PHYLOGENY OF BASAL ORNITHOPOD DINOSAURS by Rodney Dwayne Scheetz A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biological Sciences MONTANA STATE UNIVERSITY-BOZEMAN Bozeman, Montana April 1999 © COPYRIGHT by Rodney Dwayne Scheetz 1999 All Rights Reserved ii APPROVAL of a thesis submitted by Rodney Dwayne Scheetz This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the College of Graduate Studies. John R. Horner (Signature) Approved for the Department of Biology Dr. Ernest R. Vyse (Signature; 4/2-3/79 (Date) Approved for the College of Graduate Studies (Signature) Dr. Bruce R. McLeod (Date) STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a doctoral degree at Montana State University-Bozeman1 I agree that the Library shall make it available to borrowers under rules of the Library. I further agree that copying of this thesis is allowable for scholarly purposes, consistent with "fair use" as prescribed in the U.S. Copyright Law. Requests for extensive copying, or reproduction of this thesis should be referred to University Microfilms International, 300 North Zeeb Road, Ann Arbor, Michigan 48106, to whom I have granted "the exclusive right to reproduce and distribute my dissertation in and from microform along with the non-exclusive right to reproduce and distribute my abstract in any format in whole or part." Signature Date iv This work is dedicated to my mentor, Dr. James A. Jensen, for his contagious and enthusiastic curiosity. I will be forever grateful to him for sharing his eternal perspective of this world and this life. ACKNOWLEDGMENTS Without the merit of the works cited in the references, and the continuing work of Jack Horner and Dave Weishampel1 this study would not have been conceived. Much appreciation goes to Jack Horner and the NSF (EAR-9219035) grant funded to him, Barbara Lee, the Dinosaur Society, and Museum of the Rockies for supporting this study. The illustrations were provided through the talents of Frankie Jackson, who together with Jack Horner, Dave Varricchio, Kristin JuneMe, Mary Schweitzer, Yoshi Katsura, Kristi Currie, Oliver Rauhut, Dan Brinkman, Dale Winkler, and Bob Bakker, served as a sounding board for ideas and discussion. Their insight and suggestions are greatly appreciated. Prompt and meticulous preparation of specimens and histological slides were accomplished through the talents of Carrie Ancell and Ellen Lamb. Brooks Britt and Nita Kroniger provided the nagging and technical support needed to finish, and they deserve much credit. I am grateful to Ken Statdman, Cliff Miles, Lou Jacobs, Mary Dawson, Mark Norell, Hans Peter SchuItze, Angela Milner, Jon Storer, Hans-Dieter Sues, Chuck Schaaf, MaryAnn Turner, and Michael Brett- Surman for letting me study specimens in their care. Thanks goes to my committee members: Jack Horner, Dave Weishampel, Kevin O’Neill, Matt Lavin, Jim Schmidt, Lynn Irby, and Sandy Osborne. Most importantly is the support provided by my best friend and wife, Wilfreta, who, among the many things she did, insured I not miss-out on having a life while in the trenches of a dissertation. TABLE OF CONTENTS Page LIST OF TABLES ......................................................................................................... ix LIST OF FIGURES.........................................................................................................x LIST OF NOMENCLATURE AND ABBREVIATIONS............................................. xi LIST OF INSTITUTIONAL ABBREVIATIONS....................................................... xiv ABSTRACT................................................................................................................. xv INTRODUCTION ..........................................................................................................1 Previous Work on Orodromeus .......................................................................1 Stratigraphic C on tex t............... Heterochrony............................ Specimens used for Description ORODROMEUS DESCRIBED........................................................................ 10 Orodromeus Morphology............................................................................... 10 The S k u ll...............................................................................................10 Premaxilla..................................................................................10 Maxilla ......................................................................................14 Lacrimal ....................................................................................17 Supraorbital ............................................................................. 17 Prefrontal ..................................................................................19 Frontal .................................................. 19 Parie ta l......................................................................................20 Postorbital .............................................................................21 Juga l..........................................................................................22 Quadratojugal...........................................................................23 Quadrate ................................................................................. 24 Squamosal............................................................................... 25 Supraoccipital.................................................................... 25 Opisthotic and exoccip ita ls.....................................................27 Prootic ......................................................................................28 Laterosphenoid.........................................................................29 Basisphenoid ............................................................... 29 Pterygoid, palatine, and vom e r.............................................. 30 CO LO CD TABLE OF CONTENTS-Continued Basioccip tia l.............................................................................31 Dentary..................................................................................... 31 Elements of the Posterior Jaw .............................................. 33 The Postcrania ................................................................................... 34 Proatlas, Atlas & A x is ...................................................... 34 Cervical Vertebrae ..................................................................36 Dorsal Vertebrae ....................................................................41 Sacral Vertebrae ....................................................................45 Caudal Vertebrae ....................................................................47 Scapula ................................................................ 50 Coraco id ................................................................................... 52 Sternal ................................................................ 53 Humerus................................................................................... 53 Ulna............................................................................................55 Radius ..................................................................................... 55 Manus............................................................................ 55 Ilium ..........................................................................................55 Isch ium ......................................... 57 Pubis . ......................................................................................59 Fem ur....................................................................................... 61 T ib ia ..........................................................................................65 Fibula ....................................................................................... 68 Ankle ....................................................................................... 68 Foot ............... " ......................................................... .........70 O ntogeny......................................................................................................... 73 Histology ......................................................................................................... 77 Dryosaurus Ontohistology..................................................................79 Orodromeus Ontohistology...................................................... 85 Comparative Growth R a tes ................................................................89 PHYLOGENY..............................................................................................................92 Ornithopod C lassification...............................................................................92 Methods ............................................................................................................99 Resu lts .................................................................................... 100 Character Summary .............................................. 100 Evolutionary Trends .........................................................................103 REFERENCES C ITED .............................................................................................107 APPENDICES...........................................................................................................121 Appendix A — Orodromeus Specimens S tudied......................................122 Appendix B — Taxa, Specimens, & References......................................128 vii TABLE OF CONTENTS — Continued Appendix C — Phylogenetic Analysis................... 134 Cladogram of Basal Ornithopod Phytogeny...................................135 Phylogram of Basal Ornithopod Phytogeny...................................136 Apomorphy L is t..................................................................................137 Apomorphy Explanations................................................................. 144 Cranial Characters................................................................ 144 Postcranial Characters..........................................................169 Data M atrix ........................................................................................ 184 viii ix LIST OF TABLES TABLE I. Ontogenetic Changes.............................. ............................................ 75 TABLE 2. Transitional Changes.......................................................................... 105 LIST OF FIGURES FIGURE 1. Relative abundance of Orodromeus elements.....................................3 FIGURE 2. Phytogeny of the basal ornithopods...................................................... 7 FIGURE 3. Skull of Orodromeus makelia type specimen................................... 11 FIGURE 4. Orodromeus makelai skull reconstruction......................................... 12 FIGURE 5. Orodromeus maxilla ..............................................................................14 FIGURE 6. Orodromeus tee th .............................................................................. 16 FIGURE 7. Orodromeus skull elements............................. 18 FIGURE 8. Orodromeus jugal......................................................................... 22 FIGURE 9. Orodromeus neurocranium.................................................................. 26 FIGURE 10. Orodromeus mandible without predentary.......................................31 FIGURE 11. Orodromeus anterior cervical vertebrae........................ 37 FIGURE 12. Orodromeus mid- and posterior cervical vertebrae..........................38 FIGURE 13. Orodromeus nbs ................................................................................. 40 FIGURE 14. Orodromeus anterior and mid-dorsal vertebrae.............................. 42 FIGURE 15. Orodromeus posterior dorsal vertebrae........................................... 43 FIGURE 16. Orodromeus vertebral measurements............................................. 44 FIGURE 17. Orodromeus sacrum ...........................................................................46 FIGURE 18. Orodromeus caudal vertebrae and chevrons.................................. 49 FIGURE 19. Orodromeus scapula...........................................................................51 FIGURE 20. Orodromeus coracoid and sternal.....................................................52 FIGURE 21. Orodromeus humerus................. 54 FIGURE 22. Orodromeus ulna and rad ius............................................ 56 FIGURE 23. Orodromeus manus............................................................................ 57 FIGURE 24. Orodromeus ilium ............................................................... 58 FIGURE 25. Orodromeus ischium ........................................................................ 59 FIGURE 26. Orodromeus pub is .............................................................................. 60 FIGURE 27. Orodromeus fem ur.............................................................................. 63 FIGURE 28. Orodromeus femur ends ................... 64 FIGURE 29. Orodromeus tibia and fibu la ........... ................................................... 66 FIGURE 30. Orodromeus ankle............................................................................... 69 FIGURE 31. Orodromeus pes...................................................................................71 FIGURE 32. Dryosaurus histological sections of fem u..................................... 83 FIGURE 33. Orodromeus histology of hatchling femur....................................... 86 FIGURE 34. Orodromeus femur histology............... .............................88 FIGURE 35. Orodromeus and Dryosaurus growth rates..................................... 90 FIGURE 36. Previously published basal ornithopod phytogenies........................94 FIGURE 37. Othnielia rex dentary tee th ....................................... 101 LIST OF NOMENCLATURE AND ABBREVIATIONS Abbreviations Used in Figures ac: acetabulum an: angular ANKYL: Ankylosauria ant: anterior aof: antorbital fenestra bo: basioccipital brs: brevis shelf C: Camptosaurus c: cervical vertebra c-: indicates contact for given bone. For example c-mx is maxillary contact. CA: “Camptosaurus” Ieedsi cap: capitulum cdI: caudal vertebra cdIr: caudal rib CERAT: Ceratopsia ch: chevron (haemal arch) cn: cnemial crest CU: Cumnoria (“Camptosaurus”) prestwichi D: Dryosaurus and Dysalotosaurus d: dorsal vertebra de: dentary diap: diapophysis of vertebra dp: deltapectoral crest E: Echinodon en: external nares F: Fabrosaurus FABR: Fabrosauridae fm: foramen magnum fo: foramen ovalis fr: frontal G: Geranosaurus and Lychorhinus gt: greater trochanter H: Heterodontosaurus HADR: Hadrosauridae he: haemal canal X ll LIST OF NOMENCLATURE AND ABBREVIATIONS--Continued hd: head METER: Heterodontosauridae HY: Hypsilophodon HYPSIL Hypsilophodontidae I : Iguanodon ic: intercentrum of axis IGUAN: Iguanodontidae ip: iliac peduncle isp: ischiac peduncle ju: jugal L: Laosaurus lag: line of arrested growth (histology) lat: lateral Ic: lateral condyle leg: line of changed growth (histology) LM: “Laosaurus” minimus It: lesser trochanter ltf: Iaterotemporal fenestra mec: medial condyle med: medial mx: maxilla na: nasal ns: neural spine obf: obturator foramen obp: obturator process od: odontoid process op: opisthotic P: Pisanosaurus PA: Pachycephalosaurus pa: parietal PACHY: Pachycephalosauridae pal: palpebral (supraorbital) pap: parapophysis of vertebra pd: predentary PK: Parksosaurus pmx: premaxilla po: postorbital post: posterior poz: postzygapophysis PS: Psittacosaurus PSITT: Psittacosauridae X lll LIST OF NOMENCLATURE AND ABBREVIATIONS--Continued pp: pubic peduncle prf: prefrontal pro: prootic prp: prepubic process prz: prezygapophysis qj: quadratojugal qu: quadrate r: rib S: Stegoceras s: sacral vertebra sa: surangular sc: scapula soc: supraocciptal sq: squamosal STEG: Stegosauria T: Tenontosaurus TH: Thescelosaurus tub: tuberculum tvp: transverse process W: Wealden hypsilophodont undescribed Y: Yaverlandia XlV LIST OF INSTITUTIONAL ABBREVIATIONS AM - Australian Museum, Sydney AMNH - American Museum of Natural History, New York BM(NH) - British Museum (Natural History), London BYU - Brigham Young University Earth Science Museum, Provo, Utah CM - Carnegie Museum, Pittsburgh, Pennsylvania CPS - Colorado Paleontological Society at University Museum, University Colorado, Boulder DNM - Dinosaur National Monument, Jensen , Utah HMN - Humbolt Museum fur Naturkunde, East Berlin LACM - Museum of Natural History, Los Angeles County MCS -Museum of Cinco Saltos, Rio Negro Province, Argentina MCZ -Museum of Comparative Zoology, Harvard University, Cambridge MIWG — Museum of the Isle of Wight Geology, United Kingdom MNA - Museum of Northern Arizona, Flagstaff MNHN - Museum National d'Histoire Naturelle, Paris MOR - Museum of the Rockies, Bozeman, Montana MUCPv - Museum of the Universidad Nacional de Comahue, Neuque Province, Argentina MWC - Museum of Western Colorado, Grand Junction NMC - National Museum of Canada, Ottawa PU - Princeton University, New Haven, Connecticut QM - Queensland Museum, Brisbane, Australia ROM - Royal Ontario Museum, Toronto SAM - South African Museum, Cape Town SDSM - South Dakota School of Mines and Technology SMU - Southern Methodist University, Dallas, Texas T - Museum of the Geological College of Chengdu, Peoples’ Republic of China USNM - United States National Museum, Washington D.C. YPM - Peabody Museum Natural History, Yale, New Haven ZDM - Zigong Dinosaur Museum, Sichuan Province, Peoples’ Republic of China ABSTRACT The small Upper Cretaceous ornithopod dinosaur Orodromeus makelai, possesses many tooth traits reminiscent of Triassic fabrosaurs. Determining whether these teeth were retained from a primitive lineage or independently derived within Orodromeus prompted a critical examination and ultimate revision of hypsilophodontid and basal ornithopod phytogeny. The revision of the Hypsilophodontidae resulted in a dissolution of the group into a pectinate grade of dinosaurs with a concommitment trend in increased size and herbivorous efficiency. Phylogenetic context reveals Orodromeus as nested within ornithopods with established herbivorous adaptations. Anomalous triangular teeth and high angle occlusion in Orodromeus is thought indicative of a shift to insectivory, possibly retained from the neonate condition. Otherjuvenile conditions, such as large orbits and unfused elements in mature specimens, together with rapid deacceleration of radial femoral bone growth through ontogeny is suggestive of neoteny. Continued histological studies of fossil taxa, together with a clear understanding of relationships, would help to identify heterochronic shifts in evolution. Analysis of 20 taxa, using 124 morphological characters, indicates the pandemic distribution of small ornithopod taxa occurred prior to the Upper Jurassic. Although hadrosaurs diversified in the Upper Cretaceous as did angiosperms, most all major herbivorous adaptations were in place within ornithopods prior to the first occurrence of angiosperms in North America. IINTRODUCTION A small ornithopod dinosaur from the Two Medicine Formation of Montana, Orodromeus makelai Horner & Weishampel 1988, demonstrates unusual primitive features for an Upper Cretaceous “hypsilophodontid.” The description of its somewhat anomalous characteristics prompted a closer examination and ultimate revision of the group’s definition and phylogeny. This small quasi-herbivorous biped is represented by virtually complete skeletons and partial skeletons depicting several growth stages. For paleontological studies, these specimens provide a rare opportunity to compile a large suite of characters needed to run computer-generated phylogenetic analyses and to document variation and ontogenetic change within a taxon. In doing so, this study combines a thorough phylogenetic analysis of basal ornithopods with histological and morphological changes through ontogeny, to demonstrate the utility and the role of heterochrony in the evolution of ornithopod dinosaurs. Previous Work on Orodromeus Orodromeus makelai was a key taxon in studies comparing life-history syndromes in dinosaurs (Horner, 1982, 1984a, 1987; Horner & Weishampe!, 1989; Weishampel & Horner, 1994). Inferred and circumstantial evidence of growth and behavior implied from nesting horizons of this small ornithopod was 2compared to evidence found in the hadrosaur Maisaura peeblesorum Horner and Makela, 1979. Both of these small and large ornithopods are abundantly preserved within the Late Cretaceous strata of the Two Medicine Formation of Montana. Comparisons of nesting patterns and bone histology between the two ornithopods suggested Orodromeus was a relatively precocial animal, developed enough upon hatching to leave the nest (Horner and Weishampeli1 1988). ! Recent discoveries, however, have shown the sites previously assumed as Orodromeus nesting areas, to be nests of the small carnivorous dinosaur, Troodon formosus Leidy, 1856 (Varricchio and others, 1997). With the identity of the nests established, an alternative reason for the presence of abundant young Orodromeus carcasses in a Troodon nesting area may be because Troodon adults brought these small herbivores in as prey items for their young. If this were the case, a bias toward a greater number of hind- limb elements would seem likely, as the hind-quarters of the animal would constitute the largest meat mass. A crude assessment of the abundance of element-types indeed show the elements that occurred more frequently were those skeletal regions that would have been covered with more muscle mass (Figure 1). Interestingly, with the exception of only a few elements, the bones !,j representing the broad growth series of Orodromeus that come from these sites t ; j are not tooth-marked. Despite the changing views on Orodromeus eggs and nests, embryonic and hatchling Orodromeus bones remain good standards for a precocial model. 3Abundance of Elements Orodromeus makela i hindlimbneck forelimb Elements from Head to Tail FIGURE 1. Relative abundance of skeletal elements on the Egg Mountain site of the Two Medicine Formation. Highest peak represents femora and tibiae as most abundant, with scapulae and ilia occurring in about 10% of the specimens Bone histological studies on embryonic and juvenile Orodromeus specimens reveal well-developed limb ends (see histological section), suggestive of an animal capable of active physical activity upon hatching. Stratigraphic Context Nearly all the available Orodromeus material comes from the Upper Campanian Upper Two Medicine Formation of Teton County, Montana. This formation is an eastward thinning, proximal alluvial facies of the Western Interior foreland basin. Representative of the western upper coastal plain of the north- south Cretaceous seaway, the Two Medicine Formation was bounded to the east by the Cordilleran thrust belt and to the west, by the Sweetgrass Arch and distal coastal plains of the Judith River Formation. The middle portion of the Two 4Medicine and Judith River Formations are time-equivalent facies but are separated by the structural high of the Sweetgrass Arch which was active enough during the Campanian to disrupt east-west drainages, but not high enough to shed sediments (Lorenz & Gavin, 1984). Stratigraphically, the Two Medicine Formation is bounded above and below by regional unconformities and transgressive marine and marine-influenced strata. Radioisotopic dates obtained from 40ArZ39Ar analyses of biotite and plagioclase from bentonitic beds throughout the Two Medicine Formation have bracketed an age of 75 to 80 Ma (Rogers, Swisher, & Horner, 1993). Within the Willow Creek Anticline, at the Egg Mountain and Egg Island sites, several growth stages of young Orodromeus have been discovered among eggs and nests within a soil caliche horizon peripheral to, or on an island within, alkaline lake deposits (Horner, 1984a 1987; 1988; Lorenz & Gavin, 1984). Only a few Orodromeus specimens have been recovered from near the top of the Two Medicine Formation in the Landslide Butte area, near the Montana-Alberta border. Here, the upper 100 meters Of the Two Medicine Formation is exposed, but it is overlain unconformably by the Bearpaw Shale and has been determined . by Lorenz (1981, 1984) as time-equivalent to those strata in the Willow Creek Anticline area. Other time-equivalent strata of Montana and surrounding areas yield little material referable to Orodromeus. About a dozen teeth from the Judith River Formation, originally ascribed as the earliest occurrence of Thescelosaurus by 5Sahni (1972), has been recently referred to Orodromeus by Galton (1995). Galton had previously identified these teeth, as well as an additional tooth (MCZ 3729) found from the Bug Creek anthills of the Maastrichtian Hell Creek Formation (Estes and others, 1969) as from a fabrosaurid ornithopod (Weishampel & Weishampel, 1983; Russell, 1984; Sullivan, 1987). The cheek teeth (AMNH 8536, 8537; MCZ 3729) illustrated by these authors are very similar to those found in Orodromeus in being smoothly triangular, having steep double wear surfaces, and a denticulate cingulum. The type specimen Laosaurus minimus Gilmore (1924) is probably referable to Orodromeus, although it is known from little material (Sues & Norman, 1990). Found in the Campanian Belly River Formation of Alberta, Canada, L minimus consists of an incomplete hind-limb and a few vertebral centra. The femoral head extends medial from the posterior half of the greater trochanter and the lateral surface of the greater trochanter is flat, similar to Orodromeus and Parksosaurus. Heterochrony Studies of Upper Cretaceous dinosaur biogeography and paleoecology during eustatic sea level fluctuations has shown possible vicariance due to isolation events (Weishampel and others, 1991), rapid speciation during transgressive events (Bakker, 1977; Horner, 1984b, 1989; Weishampel & Horner, 1987; Horner and others, 1992; Varricchio, 1993), and evidence of 6peramorphosis and anagenesis during regressions (Horner, 1984b; Horner and others, 1992). These epeiric seas had profound quantitative and qualitative effects on terrestrial ecosystems while provincializing the continent. Orodromeus was an interesting inhabitant of the western North American continent during this time. This Late Cretaceous dinosaur is unusual for having retained primitive characters thought lost in its lineage 90 million years prior. Interestingly, this study shows Orodromeus, together with Zephyrosaurus, to be an offshoot lineage of some of the most primitive ornithopods (Figure 2). However, even in phylogenetic context, Orodromeus remains anomalous in its triangular tooth shape and high angled occlusion surfaces (see Morphologic Description) similarly found in Early Jurassic fabrosaurs. Unlike fabrosaurs, the cheek teeth in the first ornithopods are positioned close enough together they touch along the lower half of their crowns. Basal ornithopods like Yandusaurus, Othnielia, and Zephyrosaurus possess teeth with flatter and unidirectional occlusal surfaces than seen in Orodromeus. In all basal ornithopods, contacts between lateral skull elements allow limited movement, indicating a pleurokinetic skull has developed (Sues, 1980; Norman, 1984; Weishampel, 1984; Norman & Weishampel, 1991). Although similar contacts between elements are found in Orodromeus, independent and high angle occlusal facets on teeth indicate no translational movement of opposing jaws occurred. This occlusal pattern is reminiscent of that seen in mammalian insectivores (Rensberger, 1986). In non­ mammalian herbivores insectivory is typical of a neonate state (White, 1985). If 7ScuteHosaurus Lesothosaurus Heterodontosaurus AgHisaurus Yandusaurus Othnielia Orodromeus Zephyrosaurus Thescelosaurus Parksosaurus Bugenasaura Hypsilophodon Gasparinisaura Tenontosaurus Rhabdodon Dryosaurus Dysalotosaurus Camptosaurus lguanodon Ouranosaurus FIGURE 2. Cladogram of the phytogeny of basal ornithopods based on this study. 8insectivory was the neonate condition in herbivorous dinosaurs, and if Orodromeus was insectivorous as the teeth suggest, then the known specimens of Orodromeus are either young animals, or, adult animals that have retained the juvenile state throughout their growth. Retention of juvenile traits would suggest Orodromeus was neotoneus, where traits experienced a decreased rate of development, or progenic, having features arrested earlier than the ancestral condition. The cause for such developmental changes is speculative. However, it is conceivable that in context to the habitat bottlenecks during transgressive stages of the Cretaceous Sea, competition with low browsing hadrosaurs, ceratopsians, and ankylosaurs could have imposed adaptive pressures on diminutive herbivores like Orodromeus. Identifying evolutionary shifts in the timing of growth and development is difficult. Indeed, even to determine whether fossil remains are from a young larger animal or an older small animal has been subjective. Size does not always correspond well to age. Age classes have traditionally been determined based on allometry relative to known trajectories of other taxa, degree of ossification and fusion, and shape of articular ends (Ostrom, 1978; Callison & Quimby, 1984). Brinkman (1988) observed a substantial overlap in size relative to development, even in closely related taxa. This could be an especially confusing application when dealing with small animals like Orodromeus. One approach in assessing an ontogentic stage is by documenting histological development. Even though exact skeletalchronology has not been 9determined for the Dinosauria as it has been in other many other vertebrates (see Peabody, 1961), a relative ontogenetic stage is discernable (Reid, 1981; Ricqles, 1983; Chinsamy, 1991, 1993; Varricchio, 1993). When projected growth rates are compared across taxa, bearing in mind their phylogenetic context, a clearer understanding of adaptive changes will appear (see Histology). Specimens used for Description Primarily, four specimens were used for descriptive and comparative purposes: the type specimen, MOR 294, consists of a nearly complete juvenile skeleton without hands and tail; the smaller MOR 661 postcranial skeleton is about 60% complete, and probably represents a near-hatchling stage; MOR 473 is a disarticulated skeleton with a crushed skull and represents a mature animal; and MOR 663, a fairly mature disarticulated individual, has nearly every portion of the skeleton represented at least in part. Description of elements was enhanced by important comparative material of 99 other Orodromeus specimens (See Appendix A), consisting mostly of partial individual animals, or several elements of many individuals collected in a specific area. 10 ORODROMEUS DESCRIBED Orodromeus Morphology The Skull An excellent, although somewhat flattened juvenile Orodromeus skull exists for the holotype specimen MOR 294 (Figure 3). Most cranial elements are clearly visible in this specimen, although the rostrum is missing. Except for important clues from a crushed premaxilla in MOR 436, little can be determined of the tip of the skull. No evidence is provided by any other specimen as to the shape and extent of the nasals or predentary, so the rostral architecture of this area is hypothetical. Preparation of several broken and disarticulated skull elements of MOR 473 provided a more mature cranial reconstruction (Figure 4) than the juvenile holotype. The overall skull is triangular in lateral view, with a large orbit. The postorbitals extend laterally to produce a wider orbit posteriorly, and together with the frontals and prefrontais, are laterally sharp with a smoothly beveled orbital border, indicating the eye filled the orbit and bulged somewhat from the face. A supraorbital bone extends half-way across the.orbit, directly opposite an inflated tabular extension of the postorbital. A large infratemporal fenestra occupies most of the posterolateral skull behind a prominent horn-like jugal boss. Most of the cranial elements are relatively slender. Even in dorsal view, the 11 FIGURE 3. Skull of Orodromeus makelai type specimen. Skull of juvenile in right lateral view (IVIOR 294). Rostrum is missing. Key to abbreviations is given in List of Nomenclature. posterior skull is moderately narrow, tapering further towards the rostrum. The dentaries have roughly parallel upper and lower margins and the relatively long mandibular elements posterior to the coronoid slope gently to the glenoid fossa. Teeth are noticeably pointed and are not packed within the upper and lower jaws. The tip of the premaxilla comes to a blunt point with the first of five premaxillary teeth erupting from the front of a modestly everted oral margin. FIGURE 4. Orodromeus makelai skull reconstruction. Reconstructed left lateral view based on mature individual, MOR 436. Key to abbreviations is given in List of Nomenclature. 13 Premaxilla. Only two specimens with partial premaxillae are known. MOR 436 has a crushed, nearly complete pair of unfused premaxillae exposed in matrix. Only the right side is useful for description. Unlike most basal ornithopods, the lateral edge is everted or shelved, extending anteriorly to a narrow, bluntly rounded rostrum. Five premaxillary teeth are present on one side, the most anterior erupts from the rostral end, as in Bugenasaura (Galton, 1995). The anterodorsal process of the premaxilla is broken, with only the base preserved and measures 1/4 of the ventral premaxillary length. MOR 623 preserves only a posterior portion of the right premaxillary bone which bears two complete and one partial tooth crown. The teeth point ventrolabially. The posterior corner of the premaxilla ends .in a rounded buttress that was backed by the anterolateral boss of the maxilla when articulated. Preserved portions of the palate are flat, terminating in a finished edge rostral to the last premaxillary tooth. The base of the maxillary process in MOR 623, rises from the posterior half of the premaxilla. Premaxillary tooth crowns possess a bulbous base, slightly concave lingual faces, and weak longitudinal striations across the highly convex labial side. Both mesial and distal carinae bear very small denticles, the distal carina being more developed. Premaxillary teeth vary slightly in shape, but are all nearly the same size from rostral to rearward in MOR 436. These Orodromeus teeth compare favorably to those described for similarly sized ornithopods. 14 Maxilla. In the largest available specimen, MOR 473, the maxilla bears a prominent anterolateral boss before the anterior blade sweeps medially, then anteriorly to a pointed ramus. In the smaller holotype, the anterolateral boss is not as distinct (Figure 5). The flattened anteriorly-projecting ramus articulates with the opposing maxillary ramus along a sagittal suture and enters into the posterior end of the premaxilla above the palate, probably in conjunction with the vomers as in Hypsilophodon (Gallon. 1974). The ventral alveolar edge is straight and set more mesially in the posterior end. A small nutrient foramen is positioned dorsolateral to each alveolus. The jugal rides upon the posterior third of the maxilla above a medial horizontal shelf that bears faint, parasagittal striations, marking the palatine contact. In medial view, the maxilla is arched above the alveolar edge suggesting the soft palate was arched as well. Above and slightly posterior to the anterolateral boss, the thin lateral sheet of the maxilla ascends and turns posteriorly to meet the anterior ramus of the lacrimal, defining the posterior border of the antorbital fossa. The somewhat triangular antorbital fossa is centered high within the mid-portion of the maxilla, bounded dorsally and posteriorly by the lacrimal, with a ventral edge extending mxap FIGURE 5. Orodromeus maxilla. Right maxilla in lateral view (MOR 294) Key to abbreviations is given in List of Nomenclature. 15 nearly as low as the ventral edge of the orbit. The inside wall of the antorbital fossa is a thin sheet of bone which had been damaged in the holotype, making the shape of the interior, antorbital fenestra unclear, but it appears situated within the posteroventral portion of the fossa. Together, the medial and lateral walls of the maxilla define a dorsal groove within the body of the maxilla similar to that of Zephyrosaurus. The medial wall of the maxilla is poorly defined and damaged in observed specimens, but unlike most ornithopod taxa, the medial wall appears to have been short and thick. In Dryosaurus and Bugenasaura, the inner maxillary wall is more developed than the lateral, but both ascending walls are short. Due to missing teeth and obscured or eroded alveoli, the tooth count of the holotype is uncertain. However, assuming teeth are evenly spaced throughout, the length of the dentary suggests the young holotype probably retained ten teeth (13 in the larger MOR 473), Few maxillary teeth are preserved in available specimens of Orodromeus. The crowns are triangular and laterally compressed (Figure 6). Maxillary crowns are nearly symmetrical with the apex situated only slightly anterior. They vary from slightly taller than wide, to wider than tail, with small denticles along each carina unsupported by ridges. Labially, the body of the crown is slightly concave above a moderately developed cingulum. Maxillary tooth roots are straight and swollen, with a distinct neck below the cingulum. As with those of the dentary, crowns are situated within the maxilla en echelon, with the anterior crown lapping outside the mesial edge of the one behind. 16 FIGURE 6. Orodromeus teeth. A) Maxillary teeth in labial (lateral) view (MOR 613). B) Dentary teeth in labial (lateral) view (MOR 248). C) Dentary tooth in lingual view (PU 23247). D) Dentary tooth in lingual view (PU 23247). Key to abbreviations is given in List of Nomenclature. 17 Lacrimal. Only two partial Iacrimals are available for this study: the ventral portion of the right lacrimal on the holotype MOR 294 and a partial left on of MOR 623. The incomplete lacrimal on the holotype demonstrates little, other than showing the ventral ramus prevents the jugal from participating with the antorbital fossa. The lacrimal-jugal contact is a thin butt joint on the anterodorsal corner of the jugal, lapping the maxilla posteriorly. The posterior margin of the lacrimal is sharp-edged, and together with the prefrontal, forms the anterior border of the orbit. Available Iacrimals are poorly preserved anteriorly and dorsally; however, articular surfaces on the prefrontal indicate the lacrimal lapped both anterolaterally and ventrally, confining the dorsal extent of the lacrimal in a recess between the anterior and the ventral processes of the prefrontal. Neither nasals nor the dorsal processes of the premaxilla is preserved, making it impossible to determine the nature of the common lacrimal, nasal, and premaxillary contacts. Supraorbital. The palpebral, or supraorbital, is a gently bowed spike with a medially faced anterior articular end for contact with the prefrontal (Figure 7). A broad, rugose region on the posterior edge of the prefrontal indicates a ligamentous union of the supraorbital and prefrontal. The anterior articular surface of the supraorbital bears a slender anterior projection that served to brace the supraorbital and prevented significant lateral rotation. The supraorbital is slightly wider transversely than it is vertically, with a sharp lateral edge. Ventromedially, it is irregularly textured for soft-tissue attachments. Posteriorly, 18 Is socket FIGURE 7. Orodromeus skull elements. A) Left palpebral (supraorbital) in dorsal view (IVIOR unnumbered). B) Left prefrontal in lateral view (IVIOR 995). C) Paired frontals in dorsal view (IVIOR 995). D) Paired frontals in ventral view showing frontal rim of orbit (IVIOR 995). E) Left postorbital in lateral view (IVIOR 473). F) Left postorbital in medial view (IVIOR 473). Key to abbreviations is given in List of Nomenclature. 19 the supraorbital comes to a point, extending only about half-way into the orbit. Relative to the size of the orbit, the supraorbital is shorter in the younger holotype. Prefrontal. The prefrontal is a T-shaped bone in lateral view (Figure 7), forming the anterodorsal border of the orbit and connecting the skull roof to the lateral face. The concave posterior surface bears a small foramen high into the orbital area. Posterodorsally, the prefrontal is formed into a sheet of bone with a long oblique contact with the anterolateral portion of the frontal. Rostrally, the suture narrows and is vertically oriented. The tongue-shaped rostral process of the prefrontal slopes ventrolaterally and is marked by longitudinal striations on its end, either for contact with the nasals or posterodorsal process of the premaxilla. Inferior to this anterior process is the lacrimal contact. A faint irregular rugosity posterior to the highest extent of the lacrimal likely held the supraorbital. Anteriorly, along the length of the ventral process, an oblique lap joint occurs, extending down the posteromedial edge of the lacrimal. Medially, the upper half of the prefrontal is transversely concave. Frontal. The frontals are elongate plates of bone nearly 2.5 times longer than wide (Figure I) . The frontals unite along the sagittal plane, meeting more thinly in the posterior third by deep vertical striations, and anteriorly by longitudinal rugae. A deep, prominent, striated groove along the superior anterolateral edge of each frontal is the prefrontal contact. Rostrally, this contact 2 0 is more laterally positioned, resulting in a vertical contact near the anterior end. The superior surface of the frontals is convex, being highest over the orbit. Posteriorly, the superior surface curves down to meet the parietals in an irregular transverse suture, turning slightly posteriorly at medial plane. This frontal- parietal suture is a short scarf joint, with the frontals slightly overlapping the parietals. A short dorsal groove occurs on the posterolateral corner of the frontal for the postorbital articulation. Conspicuous striations within the groove are posterolaterally oriented. Ventral to this groove and laterally directed, is a complex tongue-and-groove arrangement marking the ventral postorbital contact. Ventrally below this, a firm articular attachment occurs for the laterosphenoid. Common among some small ornithopod dinosaurs, a synovial socket occurs at the underside of the parietal-frontal-postorbital triple-junction. However, no socket occurs within the frontals of Orodromeus for the head of the laterosphenoid. The frontals, together with the parietals, form the dorsal roof of the braincase. Ventrally, the medial hour-glass shaped portion of the frontals is concave, wider and deeper posteriorly, and bordered on either side by a ridges formed by the ventrolateral concavities of the orbits. Parietal. Only two specimens are preserved with parietals in the available material: a complete pair in holotype MOR 294 (although somewhat crushed), and the right parietal in MOR 473. The parietals are paired elements forming the posterodorsal roof of the braincase. Although they appear fused in the type 21 specimen, the elements in the larger MOR 473 are not fused, exposing their common broadly thick sagittal contact. Sereno (1991) observed separate parietals in Lesothosaurus, and suggested that this is a rare feature among ornithischians. Parietals occurring in an apparent fused condition in a juvenile of Orodromeus, and unfused in a more mature individual, indicates caution is warranted. Separate or unfused parietals may be a preservational anomaly, or, what might have been considered apparent fusion in other specimens, may be only superficial. The superior surfaces of the parietals are lower than the frontals, sloping slightly posteriorly. The strongly concave lateral sides dip ventrolaterally about 30 degrees from horizontal and form the medial wall of the supratemporal fenestra. Among the few preserved parietals, the lateral sides meet dorsally to form a sharp sagittal crest. However, variation occurs among individuals of Hypsilophodon, the Proctor Lake ornithopod, and Dryosaurus in which the sagittal area is formed often by a narrow shelf. Variation in the dorsal apex of several supraoccipitals of Orodromeus suggest variation would occur in the parietals of this taxon as well. The ventrolateral edge of each parietal meets with the Iaterosphenoid and, posteriorly, with the supraoccipital. Postorbital. The postorbital is a triradiate element (Figure 7) that separates the orbit, infratemporal, and supratemporal fenestrae. The frontal process is most dorsally expressed, situated within a wide interdigitate ventral groove of the skull roof, perpendicular to the transverse parietal-frontal suture. 22 Ventrally, and just excluded from the frontal, a smooth synovial socket for the head of the Iaterosphenoid occurs above and posterior to the orbit. From that point, the body of the postorbital curves Iateroventrally and divides into tapering posterior squamosal and ventral jugal processes which lie in the same plane. The posterior wall of the orbit formed by the postorbital is concave with the lateral edge projecting anteriorly into the orbit. This portion is slightly striated on the edge. The orbit is expressed medially by a ridge on the under side of the frontals which continues down the inner side of the postorbital and down through the ventral process. This descending process thins and laps anteriorly (in MOR 473, laterally) onto the ascending process of the jugal, about halfway up the posterior side of the orbit. The posterior process of the postorbital forms more than half of the temporal bar, lapping the anterior process of the squamosal dorsolaterally. Jugal. Thejugal is decorated by a prominent posterolateral, somewhat dorso-obliquely oriented, boss (Figure 8). Jugal bosses vary in size and shape in Orodromeus: conical and striated, or boss FIGURE 8. Orodrometvs jugal. Rightjugal in lateral view (MOR 473). Key to abbreviations in List of Nomenclature. somewhat flattened and keeled with striations limited to ventral and lateral 23 surfaces. The relatively bar-like maxillary process overlaps the posterodorsal end of the maxilla, ending in a butt joint with the lacrimal prior to reaching the antorbital fossa. Rostrally, the jugal thins transversely and flares slightly vertically to meet the posteroventral portion of the lacrimal. A palatine shelf extends medially on the anterior process, similarly seen in Zephyrosaurus, but oriented more anteriorly. The thin, nearly rod-like postorbital process reclines slightly posteriorly, lapping posteromedial to the jugal process of the postorbital. In the larger MOR 473, the postorbital laps along the lateral surface, into a groove of the jugal process. Anterior to the ascending postorbital process, the jugal forms the broadly curved, posteroventral corner of the orbit. Posteriorly, the jugal forms the anteroventral corner of the infratemporal fenestra, curving gently into a more acute angle. The central region of the jugal is medially concave, with two nutrient foramina within the wall medial to the jugal bosses. The jugal thins into a posterior wing, fanning-out both ventromedially and posteromedially. The posteromedial portion of this wing is shallowly recessed just posterior to the ascending jugal process, similar to the position seen Zephyrosaurus, lapping extensively the lateral side of the quadratojugal. Quadratoiuaal. The sheet-like quadratojugal is roughly triangular and somewhat laterally concave where it nestles within the jugal wing of the quadrate (Figure 3 ). A substantial anterior portion of the quadratojugal is hidden from lateral view by a shallow lap joint on the medial side of the jugal, just posterior to 24 the dorsal postorbital process. The quadratojugal forms nearly half of the ventral border of the post-temporal fenestra, gently curving for a short distance up the anterior edge of the quadrate, terminating well below the squamosal. The posteroventral corner of the quadratojugal ends near the base of the quadrate. Its height overlaps less than half the quadrate, forming a posterior shallow fossa between them, but no quadratojugal foramen exists. Quadrate. The quadrate in Orodromeus makelai is a vertical, rostrally bowed, columnar element with two disproportionate bony plates emerging from its anterior edge. The lesser of the two bony plates is the lateral jugal wing which thins and projects rostrally in a similar arch defined by the posterior edge of the main body. This jugal wing begins dorsally, somewhat abruptly, a short distance below the head of the quadrate. The lower third of the quadratojugal contact is pronounced, ending just above the articular surface of. the distal condyles. There is no paraquadratic foramen. The larger, medially oriented, pterygoid wing of the quadrate emerges a short distance below the dorsal end of the main body in a more subtle, tapering fashion than that of the jugal wing. In anterior view, the pterygoid wing tapers ventromedially to contact the quadrate ramus of the pterygoid which gives the wing a ventrally skewed profile. The ventral edge of the pterygoid wing is nearly horizontal and meets the shaft of the main body well above the distal condyles. The transversely expanded distal condyles meet the mandibular glenoid with a slight lateral incline. The smaller medial condyle falls directly in line with the columnar quadrate shaft and articulates with the articular, 25 while the larger lateral condyle articulates with the surangular. The two condyles are less differentiated in the older individual. Only the lower portion of the shaft of the main body is rostro-caudally compressed, with the rest of the shaft Iateromedially compressed up through the quadrate head. The quadrate head is slightly recurved posteriorly, with a caudal buttress that is much more pronounced in the older individual. The synovial contact for the squamosal is smooth, rounded and slightly posteroventrally directed. Squamosal. The squamosal forms the posterolateral bar of the supratemporal fenestra with thinning anterior and ventral processes (Figure 3). The posterior portion is dorsolaterally broad and rolls posteriorly over the quadrate head which fits snugly into the deep ventral socket. The ventral process of the squamosal descends along the anterior third of the quadrate, high above the quadratojugal. Anteriorly, the tapering process of the squamosal meets the posterior process of the postorbital ventromedially and obliquely, and extends half-way across the upper temporal bar. Posteriorly, the squamosal rides against the parietal wing, and ventrally against the lateral buttress of the supraoccipital. Suoraoccipital. The supraoccipital backs the skull, roofing the foramen magnum at its base and narrowing dorsally as it wedges between the posteriorly arched parietal wings (Figure 9). In MOR 294, the anterodorsal end of supraoccipital, comes to a point. In MOR 473, the dorsal tip is somewhat planar, indicating the capping parietals may have possessed a dorsal shelf. 26 FIGURE 9. Orodromeus neurocranium. A) Neurocranium in occipital view (MOR 403). B) Neurocranium in anterior view (MOR 403). C) Neurocranium in left lateral view (MOR 403). Key to abbreviations is given in List of Nomenclature. With a wide sutural contact with the opisthotics posteriorly, the base of the supraoccipital sweeps anteriorly under the parietal wings to contact the laterosphenoid. The supraoccipital joins with the prootics via a strong suture. This portion of the supraoccipital has been suggested by Sereno (1991) to 27 comprise a coosified epiotic for Lesothosaurus diagnosticus. As in all hypsilophodontid-grade ornithopods, the epiotic is not a separate bone in Orodromeus, even in very young individuals. Posteriorly, the outer smooth surface of the supraoccipital lacks a sagittal crest. At the most lateral basal extent, the supraoccipital forms a square buttress at the squamosal contact. This buttress is notched dorsally and is pierced by a vertical post temporal foramen for the vena capitus dorsalis. From this foramen, and just anterior to the lateral buttress, a groove extends ventroposteriorly toward the opisthotic. Together with the underlying prootic, the supraoccipital is excavated within its medial wall by a high, deep fossa subarcuata, which housed the floccular lobes of the cerebellum (Galton, 1974) (Figure 9). Qoisthotic and exoccipitals. The opisthotics form the posterolateral walls of the bra in case, framing the sides of the foramen magnum and expanding the occiput into broad paraoccipital processes (Figure 9). Each opisthotic extends posteriorly at the base, contributing to the dorsolateral corners of the occipital condyle. If exoccipitals are present, they form an indistinct fusion with the opisthotics, even in the smallest available specimens. Ventrally, the opisthotics form a suture with the basioccipital, and anteriorly, with the prootics. These bones are articulated and appear fused in the small specimen MOR 403 and in the holotype MOR 294, but in the larger 28 MOR 473, the sutures are open. The opisthotics arch over the foramen magnum, but do not meet. Dorsomedially, they contact either side of the supraoccipitals via a wide butt joint suture. Curved, hatchet-shaped paraoccipital processes extend laterally and downward. Along the dorsal margin of these processes, a small post-temporal foramen extends anteroventrally, exiting the anterior side of the paraoccipital, just above (and in some, surrounded ventrally by) the prootic contact. Anteroventrally, a moderately deep ventrolateral fossa is partially roofed by the posterior process of the prootic. Two foramina transversely pierce the opisthotic pedicle, one situated slightly higher and posterior to the other. These foramina housed branches of the hypoglossal nerve (XII), becoming less separated as they exit laterally. Together the opisthotics and supraoccipital form the greatest surface area on the occiput. Prootic. The prootic forms the lateral wall of the braincase (Figure 9). It is taller than long and is extensively sutured posteriorly to the opisthotic, with the upper half adpressed to a narrow, triangular suture on the anterodorsal side of the base of the paraoccipital process. Posteroventrally, the prootic borders two foramina with the opisthotic - one at the base of the infra-paraoccipital lamina which corresponds to the jugular and cranial nerve XII, and the other, the foramen ovalis found just above the basioccipital articulation. Dorsally, the prootic contacts the supraorbital, internally forming, the bottom half of a deep fossa {fossa subarcuata) that occur on the walls of the brain cavity (Figure 9). 29 Laterosphenoid. The Iaterosphenoid is a triangular, arched sheet of bone, forming the anterolateral wall of the braincase. It is ventrodorsally concave on the medial side, wider posteriorly and narrowing anterodorsally along the frontal- parietal-postorbital junction. Posteriorly, the laterosphenoid butts the anterior edge of prootic and anterior edge of the side wall of the supraoccipital (epiotic equivalent; Sereno, 1991). Dorsally it forms a continuous contact with the parietal and nearly comes to a point where the parietal meets the frontal and postorbital. From this point, the laterosphenoid head is somewhat separated and turns dorsolaterally to fit in the synovial socket of the postorbital. No foramina pierce the laterosphenoid, but a depression occurs anterior to the trigeminal nerve (V) of the prootic which it borders. Basisohenoid. The basisphenoid forms a broad, immobile, transverse sutural joint with the anterior end of the basioccipital. As the anteroventral floor of the braincase, the basisphenoid angles up dramatically from the low floor formed of the basioccipital, at about 120 degrees in MOR 623 but shallower in all others. Together with the prootic, the side of the basioccipital possesses a deep, constricted, lateral fossa that leads anteroventrally to the internal carotid foramen. Below and anterior to this, pterygoid processes extend from the anterior end of the main body, both Iateroventrally and anteriority, roughly 45 degrees from the medial plane. Facets for the pterygoid occur posteriorly and ventrolaterally on the feet of these processes. The body of the basisphenoid 30 without the parasphenoid process, measures slightly longer than the basioccipital, similarly seen in Zephyrosaurus and Thescelosaurus (Galton, 1989). The parasphenoid appears as an anterior sagittal process of the basisphenoid, projecting rostrally below the orbit, ending about mid-skull. Laterally compressed, the parasphenoid expands somewhat ventrally toward its rostral end. A sharp, ventral keel extends along its length. The keel begins posteriorly within a groove between the pterygoid processes. Dorsally, a deep pituitary fossa begins anterior to the body of the basisphenoid and continues as a groove along the length of the parasphenoid, thinning rostrally. Ptervaoid. palatine, and vomer. The vomer is a long, laterally compressed tongue-shaped bone with the rostral end forming a narrow, flattened ventral shelf. This shelf joins the anterior ramus of the maxilla into the posterior end of the premaxilla, over the palate. Although the vomers are preserved out of position in the holotype, the relative length indicates they extended over the soft palate back to the palatines, just below the anterior edge of the orbit. Behind and on either side of the vomers, the sheet-like palatines attach to the posteromedial portion of the maxilla and arch ventrally, possibly touching each other over the top of the vomers posteriorly. Dorsally, the palatines for,m a wide concavity for the anteroventral portion of the orbit, with the maxilla, jugal, and lacrimal laterally bounding the concavity. Posterior to the palatines, the edge of pterygoids can be seen in the 31 matrix on the holotype detached from the basisphenoid. Basiocciptial. The basioccipital is a median element, that forms the posteroventral floor of the braincase and articulates with the vertebral column via a posteroventral occipital condyle. Dorsally, the groove of the foramen magnum comprises the central third of the occipital condyle width, and is marked at its opening by a distinctive short, square pit. Anterior to the pit, the floor of cranium widens and arches gently upward. On either side of the floor of the brain cavity deep, laterally directed sutural ridges mark the opisthotic contact. Anterolaterallyl the basioccipital articulates with the prootic with oblique sutures. A low, median ridge on the floor of the braincase extends rostrally to the basisphenoid which is anchored to the anterior end of the basioccipital by an extensive, complex suture. Ventrally, the basioccipital bears a thin keel. Dentary. The dentaries are laterally narrow bones that comprise the anterior two-thirds of the lower jaws (Figure 10). Each dentary turns medioventrally at the anterior end to meet at an obliquely inclined joint. Rostrally, the dentary is typical of primitive FIGURE 10. Orodromeus mandible without predentary. ornithischians, having Left mandibular elements in lateral view - although many teeth are broken or missing (IVIOR 294). a somewhat pointed Key to abbreviations is given in List on Nomenclature. c-pd —^ 32 end which must have fitted, between the dorsal and ventral processes of the predentary. No predentaries have been found for Orodromeus. Anteroventrally1 the predentary contact widens slightly posteriorly and measures nearly twice the length of the more steeply angled dorsal articulating surface. Along the entire anterior margin of the dentary, within the predentary articular surface, lies the Meckelian groove that extends ventrally and mesially, traversing dorsal to the medially turned tubercle that backs the ventral process of the predentary. This groove continues longitudinally on the medial side of the dentary, and widens and deepens posteriorly and is covered by the splenial. The lateral surface of the dentary is vertically convex and marked by an anteriorly directed foramen near its rostral tip, with two smaller foramina below and slightly posterior. A row of nutrient foramina occur within the lateral surface of the dentary, just ventral to the dorsal opening of each alveolus. The first few alveoli are small and begin immediately posterior to the predentary. Alveoli are circular and occur near the lateral edge rostrally, and become moderately inset along the posterior extent of the series. The ventral and dorsal margins of the dentary are relatively parallel for most of its length, ending posteriorly with a moderately high coronoid process. There are no teeth medial to the coronoid. Although complete dentaries exist for Orodromeus, many of the alveoli are obliterated, making the determination of the number of teeth difficult. The best preserved specimen (MOR 248) is slightly larger than the young holotype and has nearly complete dentaries that provide an estimate of 14 alveoli for individuals that size. It seems likely an adult had more. Teeth touch neighboring 33 teeth only at their bases. The roots of dentary teeth are straight and swollen, and slightly constricted below the crown. The crowns are triangular overall (Figure 6), laterally compressed, and are equally enameled on both sides. Teeth vary in size, with the larger teeth situated slightly posterior to mid-row. Each crown has a modestly bulbous cingulum and smooth lingual faces slightly concave on either side of a thick vertical center. The apex of each tooth is situated slightly anterior to the center of moderately steep mesial and distal carinae. The base of the distal carina of Orodromeus curves Iingually above the swollen base, very similar to the denticulate cingulum found in the Upper Jurassic Othnielia and Drinkerof North America, and in the maxillary teeth of the Lower Cretaceous Phyllodon of Spain, Ten to 12 short, weak denticles occur along each carina, more on larger teeth and considerably less on the small anterior teeth. Orodromeus dentary teeth are similar to fabrosaur teeth (Galton, 1983; Russell, 1984; Sullivan, 1987; Horner and Weishampel1 1988) in that teeth have steep, multiple wear surfaces. Teeth are typically set in an en echelon pattern. Elements of the Posterior Jaw. The posterior 1/3 of the lower jaw gently slopes posteroventrally from the coronoid and coronoid process of the dentary. The bulk of this region consists of the sheet-like surangular which is pierced high on its lateral side by the anterior surangular foramen, and lower by the posterior foramen located just anterior to the hook-like boss in front of the glenoid fossa. Medially the surangular forms a broad fossa, flanked ventrally by the angular and 34 prearticular. Typical of ornithopod taxa, the glenoid fossa is formed by the surangular and articular, while being supported below by the angular. Unlike Hypsilophodon, the prearticular in Orodromeus extends to the posterior end of the small retroarticular process, bordering the glenoid fossa medially. The Postcrania The skeleton of Orodromeus is overall typical of small primitive ornithischians and basal ornithopods in having a light-weight build, long hind- limbs and relatively large feet - considered necessary for a small, agile biped. The neck possesses a modest natural curve, holding the head away from, and higher than the body. The forelimbs are well developed in mature animals evidenced by large coracoids and a prominent scapular spine. The hands possess moderately short, but nimble digits capable of grasping. The back is narrow and is subtly arched dorsally. The pelvis consists of relatively long, slender elements with accessary support of the pubis directly to the sacrum. The femur is bowed anteriorly and much shorter than the tibia, characteristic of a femur held horizontally as in birds (Campbell & Marcus, 1992), making the leg swing primarily from the knee joint. The crus is long, with slender tibia, fibula and metatarsals. The digits of the pes are long with mobile joints and pointed unguals, capable of grasping or negotiating uneven terrain. The tail is slender and mobile. Proatlas. Atlas & Axis. Only one proatlas (MOR 473) has been identified within the available specimens. The proatlas occurs as a pair of short, wing­ 35 shaped bones, thicker in the middle and narrower at the posterior end, serving to extend the prezygapophyses of the atlas forward. These processes articulate with the occiput on the upper and outer edges of the foramen magnum, indicated by small notches on the opisthotic. The neural arch of the atlas is likewise paired. Each neural arch has a double faceted base; one ventral and only slightly posterior, to fit against the atlas intercentrum, while the other faces anterodorsally and slightly medially, to articulate with the exoccipital. The neural arch rises dorsally from the lateral edge of the intercentrum and bends medially and rostra I Iy to form a wing of the prezygapophysis. The posterodorsal corners of the neural arch are textured by ligament scars, but these rudimentary postzygapophyses do not extend posteriorly. Likewise, the prezygapophyses of the axis are weakly developed. The atlas intercentrum is twice as wide transversely as it is long, and judging from the smooth facets, was surrounded by mobile joints. Anteriorly, the atlas intercentrum is concave with a sharp ventral margin, cupping the occipital condyle. Dorsally, rugose facets for the neural arches occur on either side of a concave center. Posterior to the center, there is a smooth concave facet for articulation with the odontoid process. This facet is incised medially by a groove which runs down the posterior end of the intercentrum. In posterior view, the atlas intercentrum has a low, smoothly rounded surface to fit against a steeply inclined axis intercentrum. On each end of this surface, are low posterolateral parapophyses for the atlatal ribs. The odontoid process of the axis is an narrowing tongue of bone that 36 cradles the spinal cord to the occiput of the skull. Although articulated in the type specimen, the odontoid is not fused to the upper anterior face of the axis in any specimens. Ventrally, the odontoid is broad posteriorly with a smooth, low undercarriage that moved against the atlas intercentrum. Anteroventrally, a mobile articulation occurs with the occipital condyle by a smooth, rounded surface. Between these two convex anterior and posterior facets, a groove extends from the dorsolateral corner of the odontoid, ventrally and anteriorly, to return back up the opposite dorsolateral corner. The axis intercentrum is a wedge that projects equally anteriorly and posteriorly, inserting into the anteroventral face of the axis - the first of the more typical looking vertebrae of the series. The axis possesses an exaggerated neural arch that extends posterodorsally as a high-pitched roof over the third cervical vertebra. The postzygapophyses are well developed, and the prezygapophyses are modest. A well developed parapophysis is located at the anterolateral edge of the spool-shaped centrum. The centrum is Iongerthan wide, and in some individuals, nearly twice the width. As in most of the cervical vertebrae, the axis centrum is taller than wide and ventrolaterally concave, producing a moderate ventral keel. A weak diapophysis occurs at the base of the neural arch, above and immediately posterior to the parapophysis. The posterior face tilts slightly rostrally. Cervical Vertebrae. There are nine vertebrae in the neck of Orodromeus (Figures 11 & 12). Each centrum, from the axis on back, is strongly concave 37 ventral ridge FIGURE 11. Orodromeus anterior cervical vertebrae. A) Cervical vertebrae 2-5 in left lateral view (MOR 294). B) Same vertebrae in dorsal view. C) Same vertebrae in ventral view. Note the ventral ridge with concavities on either side. Key to abbreviations is given in the List of Nomenclature. ventrolaterally with a sharp ventral keel. The anterior faces of the centra are wider than high and heart-shaped, while posteriorly, the centra are slightly higher than wide and D-shaped (flat end up). The axis through the fourth cervical vertebrae are slightly longer and taller than the posterior four vertebrae, the middle being transitional. 38 Starting at the base of the neural arch of the axis, slightly anterior to mid­ length, the diapophyses progressively rise and lengthen laterally through the column. In the ninth cervical, the diapophysis is aligned vertically, and a slightly lateral, to the parapophysis. On the axis, the parapophysis is on the anterolateral edge of the centrum. In the next two cervical vertebrae, three and four, the parapophyses occur at the anterior dorsal corner of the centra. In cervical vertebrae five and six, the ns ventral ridge 1 cm FIGURE 12. Orodromeus mid- and posterior cervical vertebrae of mature animal. A) Cervical vertebrae 4-9 in left lateral view (MOR 473). B) Same vertebrae in ventral view. Key to abbreviations is given in List of Nomenclature. 39 parapophyses are situated slightly posterior of the anterior edge and consist of both the centrum and the anteroventral corner of the base of the neuropophyses. The last three cervical vertebrae have parapophyses extending from the anterior edge again, incorporating even more of the basal corner of the neuropophysis. In post-axial cervical vertebrae, the small, low spines rise from the high posterior portion of the neural arch just anterior to the diverging post- zygapophyses. The sharp anterior edge of spine extends down to the top of the high neural canal, while the sharp posterior edge terminates prior to the separation of the postzygapophyses. The spines rise, as do the zygapophyses, gradually in succeeding vertebrae. The prezygapophyses are much shorter than the postzygapophyses, being positioned above the anterior end of the centra. The zygapophyses become progressively larger, more widely spaced, and more inclined down the cervical column. The infra-zygapophyseal lamina, both pre- and post-, arise from the base of the neural arch. Each neural arch contacts the centrum on essentially a horizontal plane, with both the anterior and posterior peduncles participating in the articular faces of the centrum. In the ninth cervical centrum, the ventral length is longer than the dorsal, angling the terminal faces slightly. In cervical vertebrae seven and eight, the angling faces are less apparent. In the type specimen, as preserved, the articulated cervical series is strongly curved in this area. Cervical vertebrae 3, 4 and 5 slope slightly anteriorly. Few cervical ribs are preserved. In the anterior cervical ribs, the tuberculum extends anterodorsally creating an acute angle between the 40 FIGURE 13. Orodromeus cervical, dorsal and caudal ribs. A) Cervical rib in lateral view, distal end missing (IVIOR 623). B) Left rib of first caudal vertebra in dorsal view (IVIOR 623). C) Left anterior dorsal rib in anterior view (IVIOR 623). D) Left anterior dorsal rib in posterior view (IVIOR 623). E) Left posterior dorsal rib in posterior view (IVIOR 623). Key to abbreviations is given in List of Nomenclature. 41 tuberculum and the longer capitulum (Figure 13). The tip of the capitulum is small, whereas the short tuberculum forms a broader articulation with the diapophysis. When articulated, the ribs sweep out and back. Rib lengths have yet to be determined, as no complete cervical ribs are preserved. Dorsal Vertebrae. A complete series of 15 dorsal vertebrae are present in MOR 473, MOR 294, and MOR 623 (Figures 14 & 15). The anterior dorsal vertebrae differ from the posterior cervical vertebrae in that centra of the latter are not as sharply keeled, the parapophyses are high on the side of the neural arch and tucked under the transverse processes, and both the anterior and posterior faces of the centra are equadimensional. Although longer, the first six centra are the most lightly built of the dorsal vertebrae, slightly taller than wide (more so in MOR 623), ventrally keeled, and ventrolaterally concave. The next six dorsal centra are shorter, tall as wide, with weakly concave ventrolateral sides that produce ill-defined ventral keels. The last three centra are transversely rounded centrally with no keel. Dorsal vertebrae thirteen and fourteen are as short as the few previous to them, but wider than tall. The largest, dorsal fifteen, is equadimensional in height, width and length (see Figure 16). The long transverse processes of the anterior dorsal vertebrae angle dorsolaterally. At about the third or fourth dorsal, a transition occurs where the transverse processes extend horizontal with the parapophysis situated anterior to the diapophysis, rather than ventral to it. Posteriorly through the column, 42 FIGURE 14. Orodromeus anterior and mid-dorsal vertebrae. A) Anterior dorsal vertebrae 2 and 3, or 3 and 4 in left lateral view (MOR 623). B) Anterior-most vertebra in A in anterior view (MOR 623). C) Dorsal vertebrae 5-9 in left lateral view (MOR 473). D) Dorsal vertebrae 5-9 in dorsal view (MOR 473). Key to abbreviations is given in List of Nomenclature. 43 I cm FIGURE 15. Orodromeus posterior dorsal vertebrae. A) Posterior dorsal vertebrae 10-15 in left lateral view (IVIOR 473). B) Posterior dorsal vertebrae 10-15 in dorsal view (IVIOR 473). C) Posterior dorsal vertebrae 10-15 in ventral view (IVIOR 473). Key to abbreviations is given in List of Nomenclature. transverse processes arise lower on the neural arch and shorten until the parapophysis and diapophysis become one facet on the last two dorsal 44 vertebrae. These rib attachments remain centered over the centrum, except in dorsal vertebra fifteen where the single rib attachment is situated anterior of center to clear the anterior process of the ilium. Vertebral Dimensions Orodromeus MOR 473 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 Vertebra # in Axia l Column — i| mm length g height --------- width FIGURE 16. Measurements of vertebral centra through axial column of Orodromeus1 MOR 473. Centra 1-9 cervical vertebrae, 10-24 dorsal vertebrae, 25-29 sacral vertebrae, and remainder caudal vertebrae. The zygapophyses are large and widely separated in anterior dorsal vertebrae. By dorsal vertebrae 6 and 7 the zygapophyses are closer, smaller, and steeply inclined up and away from midline. The base of the transverse processes are wide, forming a broad shelf. In anterior dorsal vertebrae, this shelf slopes downward anteriorly and outside the prezygapophyses. Posteriorly, 45 the transverse processes are positioned lower on the neural arch and the parapophyses rise, the shelf widens but the slope still curves down anteriorly unlike that seen in Zephyrosaurus. The relative position of the zygapophyses is progressively lower from the first dorsal vertebra through to the fourth, then rises slightly higher in the fifth. The zygapophyses continue low until about the tenth dorsal vertebra, rising progressively again through the last. The postzygapophyses extend slightly further than the prezygapophyses. Anteriorly in the series, the neural spines are tall, transversely thin and as narrow as the transverse processes. Each spine is situated, and reclines, somewhat posteriorly. In the latter half of the dorsal series, the neural spines have squared corners and are dorsally flattened, creating an uneven lateral brim. Each spine is centered over the centrum, and in the last dorsal vertebra, measures nearly as long antero-posteriorly as the centrum. All dorsal centra have intervertebral muscle scars along the outer edge of the ends and on the ends of the ventral keels. Even on centra lacking keels, the ventral ends are rugose. The neurocentral sutures extend the full length of the centra throughout the dorsal vertebral series. Sacral Vertebrae. Orodromeus has six sacral vertebrae. The first sacral centrum is the largest in every dimension, having a broad, nearly flattened ventral surface. The other sacrals are narrow, but all are ventrally flat, the last being transitional to a more rounded ventral surface as in the first caudal centrum. In the holotype, MOR 294, the sacrals appear fused into a single unit 46 (Figure 17). However, sacral vertebrae are separate in the largest specimen available, MOR 473, so the fusion in the smaller specimens may be superficial. Ends of the centra are U-shaped with a deep neural canal. secondary pubic articulation \ sacral rib FIGURE 17. Orodromeus sacrum. Sacrum, ilia, and first caudal vertebrae in ventral view (MOR 294). Key to abbreviations is given in List of Nomenclature. The irregular surface of the anterior face of the first sacral (or sacro- dorsal) indicates a firm attachment to the last dorsal. The transverse process is short and contacts the anterior process of the ilium. The first and second sacral centra are noticeably wide where they meet, sharing a prominent ventrolateral socket below an intervertebral sacral rib. This socket is the articulation for the medial protuberance of the main body of the pubis. The sacral rib above this 47 joint served to support both the pubis and pubic peduncle of the ilium. The second sacral rib arises laterally from the anterior base of the neurapophysis on the third sacral and supports the ilium above the acetabulum. The robust third sacral rib braces the medial side of the ischiatic peduncle of the ilium. It arises laterally from the anterior edge of the base of the neurapophysis of the fourth sacral. Here, the base of the neural arch is much lower on the centrum than posteriorly. The last two longer sacral ribs rise from the neurocentral suture in the remaining sacral vertebrae, migrating more posteriorly. Both ribs flare anteroposteriorly to contact the thin, brevis shelf of the ilium. The extension of these ribs, together with the modest brevis shelf, expand the posterior portion of the pelvis. The sacral spines are transversely very thin, but broadened antero­ posteriorly, nearly coalescing with one another in MOR 623. The top of the spines do not extend above the top of the ilium when articulated and are not dorsally flattened as seen in the dorsal vertebrae. In the young holotype, MOR 294, tendons are preserved along the sides of the spines throughout the length of the sacrum. Caudal Vertebrae. Caudal vertebrae occur in about 30 specimens, but no complete caudal series, nor good articulated sections exist. And although tendons occur in the sacral series, no Orodromeus specimens preserve any ossified caudal tendons. 48 Only the holotype (IVIOR 294) and MOR 623 have good anterior caudal vertebrae. In these, the caudal vertebral ribs attach at the neurocentral suture (Figure 18) and are not fused. The first caudal rib is quite variable between specimens, some lie within the horizontal plane, others directed dorsolaterally, while others sweep more posteriorly. Anterior ribs behind the first, angle slightly dorsolaterally, and are twice as long as the centra are wide. The first caudal centrum is equadimensional, but after the second caudal vertebrae, centra are noticeably taller, with height and width decreasing distally along the tail. Ventrally, anterior caudal vertebrae possess a weakly depressed groove. Dorsally, the neural arches cover the length of the centrum, sinking deeper onto the centrum anteriorly in the anterior-most caudal vertebrae. The first chevron occurs on the posterior end of the first caudal. The first caudal vertebral spine reclines only slightly posteriorly and is situated posterior on the neural arch. Its sharp anterior edge does not continue down to the top of the neural canal. The posterior edge of the spine is broad near the base above the zygapophyses, and narrows dorsally to a sharp edge. The laterally thin and blade-like spines become progressively more reclined in succeeding vertebrae. Both the pre- and post- zygapophyses extend just beyond the end of the centra, and even in anterior caudal vertebrae, are not large. Zygapophyses get progressively smaller posteriorly in distal vertebrae and angle 25 degrees from horizontal. The mid-caudal centra are only slightly taller than wide and elongate 49 c-cdl poz poz m m 1 cm FIGURE 18. Orodromeus caudal vertebrae and chevrons. A) Anterior caudal vertebra in left lateral view (IVIOR 623). B) Anterior caudal vertebra in posterior view (IVIOR 623). C) Anterior chevron in left lateral view (IVIOR 623). D) Anterior chevron in posterior view (IVlOR 623). E) Proximal articular surface of the anterior-most mid-series caudal centrum shown in F (IVIOR 650). F) Mid-series caudal vertebrae with chevrons, all in left lateral view (MOR 650). G) Posterior caudal vertebra in left lateral view (MOR 650). H) Posterior caudal vertebra in anterior view (MOR 650). Key to abbreviations is given in List of Nomenclature. 50 (Figure 18). Some individuals possess narrower mid-caudal centra with a deeper ventral groove. Posterior chevron facets are larger than anterior. The caudal rib consists of a boss arising from the upper edge of the centrum side and is set slightly posteriorly. The neural arch is low. Zygapophyses are small and nearly vertical articular facets that extend barely beyond the centrum. Neural arches are shorter and centered on the centra. The distal caudal vertebrae retain a fairly consistent length, but appear elongate because the decreased height and width. As with the mid-caudal vertebrae, neural arches are shorter than the centra. The low neural arches lack spines. The minute zygapophyses are nearly vertical. No caudal rib exists, but for a full-length ridge along the side of the centra. Width and height are nearly equal, making The ends of the centra are nearly round in outline. The venter is weakly grooved. Scapula. The scapula is described with the blade in horizontal position for the purpose of clarity. The scapula is a slender, bladiform element that curves medially at the expanded anterior end (Figure 19). Laterally, the anterior end is broadly concave above the glenoid, and roofed by a prominent scapular spine. The blade is fairly straight, expanding gradually posteriorly. The distal end is thin, with an irregular surface, suggesting a cartilaginous extension was present in life. The superior border of the broad scapular shaft bears a sharp edge. The ventral edge of the neck is thick and rounded, becoming sharper posteriorly along the scapular blade. A prominent scapular spine begins at the dorsal edge 51 sc spine sc spine sc spine FIGURE 19. Orodromeus scapula. A) Right scapula in dorsal view (IVIOR 623). B) Right scapula in lateral view (IVIOR 623). C) Right scapula in inverted medial view (IVIOR 623). Key to abbreviations is given in List of Nomenclature. of the shaft, and becomes sharper anteriorly. The scapular spine is a wide, flattened roof projecting over the posterodorsal edge of the coracoid. Anteriorly, the articular surface for the coracoid is rugose, with radiating ridges and valleys for a tight interdigitate suture. Neither are fused however, even in the largest specimen, MOR 473. The thickest part of the scapula occurs 52 backing the glenoid. The glenoid is broad and smooth, angling 35-40 degrees posteriorly from the coracoid\scapula articulation. Coracoid. The large coracoid is a relatively flat, thin bone (Figure 20), bordered posteriorly by a thick scapular articular surface, and posteroventrally by FIGURE 20. Orodromeus coracoid and sternal. A) Left coracoid in lateral view (MOR 994). B) Left coracoid in medial view (MOR 994). C) Right sternal in ventral view (MOR 623). D) Right sternal in lateral view (MOR 623). Key to abbreviations is given in List of Nomenclature. 53 an equally large, smooth glenoid. The coracoid glenoid cavity is similar in size and shape to the other half of the glenoid formed by the scapula. Both measure 40 degrees from the scapula-coracoid articular surface, forming a 100 degree cup to house the humerus head. The glenoid cavity, when directed ventrally, orients the coracoid to angle out anterolaterally, creating an expanded pectoral I region. In the young holotype (MOR 248), the coracoid is equally dimensional in height and width, whereas in the larger individual, the coracoid is broader than long and relatively flatter. Medially, the broad coracoid is subtly concave. The lower margin of the coracoid is arched along a ventral sulcus leading to a moderate anterior hook. The coracoid foramen extends straight through the coracoid, well anterior to the scapula, with a posterior recess on the lateral side, exiting medially with a depressed dorsal rim. Sternal. Orodromeus sternals are of typical shape for primitive ornithopods (Figure 20). The flat plate-1 ike element is distinctively longer than wide, with rounded, thicker medial edges. Laterally, the edges are sharper and straighter. Humerus. The humerus in Orodromeus makelai does not differ significantly from Hypsilophodon and is typical of small ornithopods. In lateral view, the humerus is slightly sigmoidal, bending at the prominent deltopectoral crest, with the upper expanded portion extending medially and posteriorly (Figure 21). The humerus is widest at the proximal end with a centered, slightly raised 54 head. The upper third is flattened front to back, with a shallow, concave anterior face and slightly convex posterior surface. A sharp lateral edge tapers gradually down to the deltopectoral crest. Prominence of the crest is varies between specimens, becoming more extreme in larger individuals and somewhat knob­ like. The middle 1/3 of the humerus is a cylindrical shaft which is more ovoid in younger individuals. The distal end is bicondylar and marked by an intercondylar groove which is most pronounced anteriorly. The condyles are somewhat flattened and squared, with the ulnar condyle slightly larger than the radial. FIGURE 21. Orodromeus humerus. A) Right humerus in anterior view (IVIOR 294). B) Right humerus in medial view (IVIOR 294). C) Right humerus in proximal view (IVIOR 294) D) Right humerus in distal view (IVIOR 294). Key to abbreviations in List of Nomenclature. 55 Ulna. The subtly sigmoidal ulna is slightly longer than the radius. The olecranon process is moderately high (Figure 22). Proximally the ulna is triangular, with a narrower and slightly concave anterior articular end for the humerus. The ulnar shaft is oval in cross section but with a circumference equal to that of the radius. In distal view, the ulna is reniform. Radius. The radius is less distinct in having a more cylindrical shaft and only slightly expanded ends. Proximally the humeral contact of the radius is flat to slightly concave, with an roughly oval outline. Distally1 the radius is smoothly rounded and less expanded than the proximal end (Figure 22). Manus. A nearly complete articulated left manus is preserved in PU 23442 (Figure 23). The manus consists of wider-than-thick metacarpals with squared corners. Proximally the metacarpals are expanded and flattened to meet with four blocky, loosely articulated carpals. Resting against the large intermedium, the stout Metacarpal III bears the largest digit, consisting of four phalanges. Digit I is missing, as are the phalanges to metacarpal V. Preserved digits LI through IV end in pointed, terminal unguals, providing a phalangeal formula of ?-3-4-3-?. Ilium. The ilium is an elongate blade with a somewhat blunt posterior end and a ventrolaterally drooping anterior process (Figure 24). Ventrally, the ilium forms the dorsal border of the acetabulum which is positioned only slightly posterior of center, being shallow anteriorly and steeply curved posteriorly. 56 FIGURE 22. Orodromeus ulna and radius. A) Left ulna in anterior view (MOR 473). B) Left ulna in medial view (MOR 473). C) Left ulna in proximal view (MOR 473). D) Left ulna in distal view (MOR 473). E) Left radius in anterior view (MOR 473). F) Left radius in medial view (MOR 473). G) Left radius in proximal view (MOR 473). H) Left radius in distal view (MOR 473). Key to abbreviation in List of Nomenclature. The ilium bears a slight lateral shelf that roofs the acetabulum. The pubic peduncle is thin and anteroventrally directed with a flat, ventral pubic contact. Medially, this peduncle is marked by a thin articular surface for the first sacral rib. The ischial peduncle is large and ventrolaterally directed with a prominent rounded, lateral boss that forms part of the synovial contact for the femur head. Ventrally, there is a small articular facet for the ischium and a large, medial, rugose facet for union with the sacral rib. A modest brevis shelf begins at the top of the medial side of the ischiac peduncle, and widens medially to the posterodorsal end of the ilium. The posterior portion of the ilium arches laterally, ending in a narrow, blunt point. The dorsal edge of the ilium remains sharp and convex in lateral view. Laterally, the iliac blade is shallowly concave, as is the lower medial side of the anterior process. The anterior process is variable in shape, with some markedly ventrolaterally curved, and others relatively straight. Ischium. The ischium is an elongate bone which consists of a posterior straight beam (Figure 25) and a remaining proximal 2/5 portion which arches FIGURE 23. Orodromeus manus. Left hand in anterior view (PU 23442). Key to abbreviations is given in List of Nomenclature. 58 ac isp FIGURE 24. Orodromeus ilium. A) Left ilium in lateral view (IVIOR 623). B) Posterior end of left ilium showing brevis shelf (IVIOR 623). C) Left ilium in ventral view (IVIOR 623). Key to abbreviations is given in List of Nomenclature. somewhat anterodorsally and away from the sagittal plane, flaring to form the posterior acetabular border and iliac and a pubic peduncles. The dorsally directed iliac peduncle is slightly larger than the anterior pubic peduncle, being more disparate in smaller specimens. The acetabulum is gently concave. A tab­ like obturator process occurs 2/5 of the way down the sharp ventral edge of the ischium. This process curves ventrolaterally to support the rod-like posterior process of the pubis. The lateral side of the blade is flatter than the inner, 59 FIGURE 25. Orodromeus ischium. A) Right ischium in lateral view (PU 23431). B) Right ischium in dorsal view (PU 23431). Key to abbreviations is given in List of Nomenclature. forming a thinly rounded dorsal edge. The non-expanded blade is posteriorly directed, and in some specimens, curves slightly dorsal near the terminal end. This variation does not correlate with size and is likely due to individual variation. The ischium changes little through the available growth series, becoming more laterally compressed but remaining consistently Iongerthan the ilium and femur. Pubis. The pubis is delicate (Figure 26) with long, slender anterior and posterior processes. The anteriorly projecting prepubis is laterally compressed o b f F IGURE 26. Orodromeus pubis. A) Right pubis in la teral v i ew showing angu la t i on of an te r i o r and pos te r i o r b lades (MOR 623). B) R igh t pubis in ven t ra l v i ew (MOR 623). C) Lef t pubis in medial v i ew showing the pubic boss whi ch a r t i cu l a tes wi th sacrum (PU 23442) 61 and extends slightly beyond the preacetabular process of the ilium. The rod-like postpubis is straight and extends posteroventrally along the entire length of the ischium. The prepubis and postpubis meet at about 160 degrees from one another, and, in some specimens, appear as a continuous bar bending in the area of the main body. The expanded main body of the pubis forms the anteroventral margin of the acetabulum, supported dorsally by the first sacral rib and pubic peduncle of the ilium, and posteriorly by the peduncle of the ischium. Additionally, a smooth rounded boss projects medially from the main body of the pubis to pivot within a socket on the posterolateral end of the first sacral i centrum. This accessory articulation is a derived character shared with Zephyrosaurus. The pubis bears two facets for the ischium. One facet is posterior to the main body of the pubis, while a thin adjacent facet is formed along the anterodorsal portion of the postpubis. In some pubes, the posteriorly directed facet houses an open obturator foramen, while in other pubes of similar size, the ; foramen is enclosed within the body of the pubis. Individual variation occurs similarly within Hypsilophodon. Ontogenetic data for the pubis are lacking. Femur. Ontogenetically the smallest embryonic femur (T l .3 mm long) is less curved than larger femora. The head is at a right angle to the shaft and is nearly centered on a narrow greater trochanter. The lesser trochanter is incomplete but compares favorably with larger femora in that the lesser trochanter is born at the anterior edge of the greater trochanter. The position of 62 the fourth trochanter above mid-length is consistent through ontogeny, although better developed in older individuals. The smallest part of the shaft, just below the fourth trochanter is circular in cross section, similar to the femur of the hatchling (MOR 407). The distal end is relatively broad Iateromedially with a wide, posterior intercondylar groove. The lateral and medial condyles are subequal in size. In lateral view, the distal end of the femur is strongly recurved posteriorly about 45 degrees from horizontal in the.smallest and 54 degrees in the near hatchling. This is probably the embryonic condition, related to the confines of the egg. In larger available femora (MOR 623, 473) (Figure 27 & 28), the greater trochanter appears as a blade, broadly expanded anteriorly, with a flattened to nearly concave lateral side. The femoral head joins the posterior half of the. greater trochanter and angles up 17 degrees from horizontal, putting the top of the head above the greater trochanter. The lesser trochanter is juxtaposed to the cranial edge of the greater trochanter and angles more anteriorly in larger femora due to the expansion of the latter. In outline, the lesser trochanter is poorly defined, but appears nearly fused and continuous with the dorsal border of the greater trochanter. The pendant fourth trochanter is a posteroventrally directed triangular blade with a. thick ventral edge. The position of the fourth trochanter varies, occurring within the proximal 50-43%, independent of size (Scheetz & Horner, in press). Differences in the shape of the fourth trochanter also seem to be due to individual variation. A shallow pit for the insertion of M. caudifemoralis Iongus occurs on the shaft at the base of the fourth trochanter, 63 1 cm FIGURE 27. Orodromeus femur. A) Left femur in lateral view (IVIOR 623). B) Left femur in medial view (IVIOR 623). Key to abbreviations is given in List of Nomenclature. 64 1 cm mec mec FIGURE 28. Orodromeus femur. A) Left femur in posterior view (MOR 623). B) Left femur in proximal view (IVIOR 623). C) Left femur in distal view (IVIOR 473). Key to abbreviations is given in List of Nomenclature. 65 directly below the femoral head. This insertion point varies in size and shape among individuals but is consistantly more pronounced in larger femora. At mid­ length, just below the fourth trochanter, the shaft is triangular in cross-section with a gently rounded anterior corner. The shaft broadens slightly distally. The distal articular surface is rounded and is more equal in sagittal and transverse dimensions than the embryonic femora. The lateral condyle, though smaller, projects posteriorly beyond the medial condyle. Both are divided by a deep intercondylar groove. Anteriorly, there is only a subtle intercondylar depression in the larger femora. Tibia. The tibia is markedly longer than the femur and only slightly narrower at midshaft. Laterally, the tibia is straight with a anteroposteriorly expanded proximal end (Figure 29) and a transversely expanded distal end, giving the length of the shaft a twisted appearance. In anterior view, the tibia is slightly sigmoidal with a posterolaterally sloping proximal end. There is considerable variation in morphology and dimensions of the proximal end among specimens. This is partly due to preservational distortion, but individual variation is also evident. Proximally, the dual-lobed, lateral condyle is consistently larger than the expanded posterior condyle and anterior cnemial crest. The posterior lobe of the lateral condyle is the origin of a ridge that extends down the shaft for only a short distance, while the more cranial lobe forms the posterior fibular articulation. The relatively small cnemial crest rises above the flat femoral articular surface, and extends diagonally down the shaft a short distance. Its 66 FIGURE 29. Orodromeus tibia and fibula. A) Left tibia of juvenile in anterior view (PU 23250). B) Left tibia of juvenile in lateral view (PU 23250). C) Left tibia of juvenile in proximal view (PU 23250). D) Left tibia of juvenile in distal view (PU 23250). E) Right fibula in proximal view (MOR 623). F) Right fibula in anterior view (MOR 623). G) Right fibula in lateral view (MOR 623). Key to abbreviations is given in List of Nomenclature. 67 anterolateral surface serves as the proximal anterior fibular contact. In cross section, the tibial shaft is roughly triangular with rounded corners in the upper half, while distally, the shaft is fusiform with the point formed by the lateral edge of the outer malleolus. On the posterior side of sharp lateral edge, at about level of the distal fibular articulation, is a prominent attachment scar like that of Hypsilophodon and Zephyrosaurus. A muscle scar also occurs on the medial edge of the inner malleolus, though less distinct. In anterior view, both distal malleoli are separated by a long, wide ligament groove that receives the ascending process of the astragalus distally. This groove is present in Hypsilophodon and in fabrosaurs. In Dryosaurus, however, no definitive groove exists except for a gentle saddle that receives the astragalus. The anterior surface of the outer malleolus is flat, marking the distal fibula contact. The obtuse angle formed by the difference in direction between the malleoli is about 110 to 130 degrees. Although some of the smallest specimens are more anteroposteriorly compressed, there is no significant allometric correlation between decreased angle and increase in size. On this distal corner is marked the highest extent of articulation with the posterior ascending flange of the astragalus. In Dryosaurus, by contrast, this corner is the site of a notch or recess (Galton, 1981) that immobilizes the astragalus. The distal end slopes slightly laterally relative to the long axis of the shaft. By contrast, in fabrosaurs and less so in Dryosaurus, the outer malleolus extends lower. 68 Fibula. The proximal head of the fibula is laterally flattened with a concavity central to the medial side (Figure 29), spanning the space between the proximal lateral fibular condyle and cnemial crest of the tibia. The dorsal surface of the fibula slopes posteriorly. The proximal head is supported by a thick neck which tapers gradually to the laterally narrow shaft. The shaft is relatively straight; noticeably heavier in the upper half, and gradually decreasing in diameter distally. At midshaft, the cross-sectional geometry changes from a D- shape, with the flat side medial, to a slender rod that continues distally. The posterior side of the distal fibular shaft laps against the outer malleolus of the tibia and is correspondingly flattened, expanding medially to a thin sheet just above the swollen fibular foot. ' J Ankle. The calcaneum of Orodromeus is half the length of the astragalus and is similar in form to that of Zephyrosaurus. Unlike the calcaneum of Dryosaurus, the calcanei of both Zephyrosaurus and Orodromeus are confluent, and nearly fused, to the astragalus (Figure 30). The astragalus-calcaneum articular surface consists of a line of globular protrusions interrupted by vertical foramina. At the top of this articulating surface, a notch receives the diagonal branch of the ascending process of the astragalus. In lateral view, the calcaneum is circular with a swollen margin, truncated on two sides. Like the calcaneum in Zephyrosaurus, these truncated sides form an angle between them of 130 degrees. The concave dorsal side is the fibular contact. Postero- medially, a saddle cups the distal corner of the lateral malleolus of the tibia. 69 G H I 1 cm FIGURE 30. Orodromeus astragalus, calcaneum and distal tarsals. A) Articulated left astragalus and calcanuem in proximal view (MOR 997 & 999). B) Left astragalus in medial view (MOR 997). C) Left calcaneum in lateral view (MOR 999). D) Medial distal tarsal in proximal view (MOR 623). E) Medial distal tarsal in distal view (MOR 623). F) Medial distal tarsal in posterior (plantar) view (MOR 623). G) Lateral distal tarsal in proximal view (MOR 623). H) Lateral distal tarsal in distal view (MOR 623). I) Lateral distal tarsal in medial view (MOR 623). Key to abbreviations is given in List of Nomenclature. Fourteen Orodromeus specimens have astragali. In medial view, the low, boat-shape profile conforms to the underside of the squared medial malleolus of the tibia. The sharp posteriorly directed edge of the astragalus rises only slightly 70 on the medial end. Anteriorly, the forked ascending process lies within the flexor groove on the tibia. The medial fork is vertical, and the lateral is dorsolaterally directed and is partially received within a dorsomedial notch on the calcaneum. Foot. The foot of Orodromeus consists of five metatarsals -- the middle three primarily functional in weight bearing, metatarsal I being somewhat reduced and secondarily functional in weight bearing, and metatarsal V consisting of a splint (Figure 31). The phalangeal formula of the pes is: 2-3-4-4- 0. (To facilitate description, metatarsals are here described in a vertical orientation. The digits are described in horizontal orientation.) Proximally, metatarsal I is a thin blade, laterally flattened against the medial, and somewhat posterior, side of metatarsal II. Near mid-length, the metatarsal changes from a laterally flattened bone to a more cylindrical shaft, and diverges slightly anteromedially. Distally, it thickens to a single condyle supporting a slender phalanx and terminal ungual. The variable length of metatarsal I within specimens does not correlate with body size, ranging from 59% to 70% the length of metatarsal III. Metatarsal Il is one of the three central weight bearing foot elements, nearly as long as metatarsal IV but shorter than metatarsal III. Proximally the metatarsal, together with metatarsal I, rises higher than the other metapodials when articulated. This is expressed in the underside of the large medial tarsal as a step (Figure 30). The laterally compressed proximal end is wider across the front, measuring longer antero-posteriorly than other metatarsals. The medial 71 medial tarsal FIGURE 31. Orodromeus pes. Left foot in anterior view (IVIOR 530) 72 side is flattened in the upper third where the broadly thin metatarsal I presses against it. The lateral surface is flat nearly the entire length where it snugly articulates against metatarsal III. The distal end is essentially a squared single condyle incised posteriorly by a groove and laterally by a broad pit. Metatarsal Il bears two moderately elongate phalanges and a terminal ungual. Metatarsal III is the largest of the foot bones, supporting the largest digit of three non-terminal phalanges and an ungual. The proximal half is sandwiched between metatarsals Il and IV and is transitional in dimensions between the two. The bone changes from slightly laterally compressed above midshaft to laterally expanded below. The posterior side remains moderately flattened. Distally1 metatarsal III expands into two well defined condyles, marked by collateral ligament pits and a shallow dorsal extensor groove. The medial condyle is I slightly larger than the lateral condyle in the larger specimens (MOR 473) but both condyles are subequal and moderately squared in the smallest specimen • I (MOR 661). In MOR 661, metatarsal III is slightly longer than the humerus. In the holotype MOR 294, the humerus is Iongerthan metatarsal III. ■ Metatarsal IV is similar in length to metatarsal II. It appears longer ' ■ ■ I because it begins level with metatarsal III, rather than rising higher as does metatarsal II. Dorsally, metatarsal IV is triangular and concave, forming a saddle for the kidney-shaped lateral distal tarsal (Figure 30). A sharp lateral edge ' ' I descends to the distal end. The medial side remains flat against metatarsal III : for half its length, then becomes rounded as the bone diverges gently laterally I from the rest of the foot. The distal end is a slanted parallelogram in outline, j III 73 although it consists of a rounded articular surface with shallow flexor grooves on either side. Metatarsal V is a splint of a bone which is adpressed against the proximal, posterolateral side of metatarsal IV. Distally this splint comes to a thin rounded point of cancellous bone. Although no digit is preserved, the articular surface could have served as a joint for thin, cartilaginous ungual. Most non-terminal phalanges are equadimensional on the concave proximal end, but the distal end of paired condyles are slightly wider than high with deep collateral ligament pits and well defined dorsal extensor pits. Unguals are long and triangular, wider than high proximally, with a nearly flat ventral side. Deep grooves flank both side and extend to the tip of the ungual. Ontogenetically, the smallest available specimen, MOR 661, still exhibits well defined phalangeal extensor pits and flexor grooves, but the unguals begin as tall as wide and are relatively shorter. Metatarsal IV has a wider proximal end and is not as deep anteroposteriorly. The distal tarsal is marked ventrally by a step but is relatively thinner for its breadth. Ontogeny The available growth series for Orodromeus provides many important comparative tools to use in dinosaur paleontology. It allows traits to be recognized and identified as to individual variation or natural changes in morphology due to growth. This is important because taxa have been mis­ diagnosed, having been designated a distinct species based on ontogenetic or 74 sexual dimorphic characters. For example, four species of Camptosaurus were identified by Marsh (1879,1894) and Gilmore (1909) from quarry 13 of Como Bluff, Wyoming. Camptosaurus dispar, C. nanus, C. medius, and C. browni were differentiated on the relative slenderness of overall skeleton, the amount of curve in long bones, degree of fusion between elements, expansion of spines, ventral keels on vertebrae, relative size of coracoid, and the robustness of the deltoid crest on the humerus. Yandusaurus was divided into two species, Y. hongheensis and Y. multidens (He & Cai, 1983), based on the relative height of the posterior skull from the orbit, the length of the rostrum, length of the supraorbital, curvature of the quadrate, relative size of the squamosal, curvature of the humerus and prominence of the deltoid crest - all shown to be ontogenetic in Dryosaurus (Carpenter, 1994). Although not every Orodromeus element is represented multiple times within the growth series, many elements occur frequently enough in different sizes they display significant change through ontogeny. These changes are summarized in Table 1. 75 TABLE 1. ONTOGENETIC CHANGE# IN ORODROMEUS Juvenile Adult Jugal Jugal boss small to very small, individual variation evident. Ascending process resides medial and posterior to the ventral process of the postorbital. Largerjugal boss in various shapes. Lateral groove in ascending process for postorbital. Maxilla Maxillary crowns wider than tall. Anterolateral boss of the maxilla is prominent and maxillary crowns are taller. Frontals Somewhat vaulted over orbit. Even the largest, MOR 473, is curved high over the orbit. Contacts with other bones much better defined (i.e., deeper, well defined grooves ridges and facets). Supraorbital Relatively short. Longer Quadrate Straighter, up through the proximal head. Moderate distal condyles. More bowed; Distal condyles less distinct; posteriorly directed head is relatively larger Dentary Dentary taller just anterior to coronoid. Tooth crowns lower and wide. Tendency toward parallel dorsal and ventral margins; mandibular tooth crowns are higher than wide. Postorbital Laps on the anterodorsal process of the jugal (it is not clear whether this is individual variation) Large inflated area into orbit; ventral process laps in a lateral groove of the Jugal Scapula Shaft and blade relatively broader; Scapular spine angles more anterodorsally instead of being in line with the shaft and blade. Scapula and humerus -same length. Scapular spine sharply prominent and roofs coracoid; scapula is longer than the humerus. 76 TABLE 1. ONTOGENETIC CHANGES IN ORODROMEUS Coracoid Nearly equally-dimensional Broader than long; roofed posteriorly by the scapular spine. Humerus Straighter; lower shaft flattened; distal condyles more distinct; When comparing forelimb lengths to hindlimb lengths of 5 specimens across the ontogenetic growth, forelimbs exhibit positive a I Iometric growth to hindlimb length, from. 82% in MOR 661 to 89% in MOR 623 & 473. Proximal humerus much more expanded; Deltapectoral crest more pronounced and longer going from 25% (MOR 661) to 33% (MOR 294) to 43% (MOR 473) the length of the humerus through ontogeny; Shaft cylindrical and bowed; Ilium Acetabulum begins higher; sharp dorsal edge more convex in lateral view; blade appears shorter in length with a higher midblade. Acetabulum shallower; ilium longer relative to height. Ilia shape somewhat variable. Ischium Iliac peduncle larger than pubic peduncle Larger the ischium, the more the peduncles equalize; relatively thinner posterior blade. I77 TABLE 1. ONTOGENETIC CHANGES IN ORODROMEUS Femur Straighter; head, right angles to the shaft and is nearly centered on a narrow greater trochanter; shaft circular in cross-section; distal end relatively broad Iateromedially with a wide posterior intercondylar groove; lateral and medial condyles distal subequal in size; distal articular surface angles posterodorsally. Flattened blade-like greater trochanter; lesser trochanter juxtaposed to anterior edge of the greater trochanter; femoral head from posterior half of the greater trochanter and angles up 17 degrees from horizontal; fourth trochanter & insertion marks pronounced; shaft triangular in cross- section; lateral distal condyle smaller & projects posterior beyond the medial condyle. " | ' Calcaneum Angle between tibia! facet and fibular facet closer to 90 degrees; fibular facet nearly flat; relatively thinner for height and depth antero- posteriorly (less than 173 tibia end width) Angle between tibial facet and fibular facet > 120 degrees; fibular facet concave; covers over 1/3 distal tibia end,. ' | ' j ] : I ;l Histology In 1947, Amprino recognized the possibility that different histological : j structures found in primary periosteal bone resulted from changing growth rates. He suggested bone growing at accelerated rates deposits a more complex ; ;l network of vessels in a less organized matrix. A more recent study by Castenet j ■ ■ ' . I 78 and others (1996) sought to test this concept through experimental data using 21 mallard ducks. Their study substantiates Amprino’s Rule, in showing tissue type correlates with rate of radial deposition. Other growth rate data compiled by Ricqles and others (1991) indicate some variation occurs among taxa, yet whatever the species studied, compact lamellar bone was documented to grow at a rate between 0.05 and 0.30 microns/day; parallel-fibered bone grows between 0.10 and 0.50 microns/day; and woven-fibered bone, common among embryonic and very young animals, is deposited at the highest rate of 0.40 to higher than 22 microns/day. Three bone tissue-types pertinent to the study of Orodromeus histology are defined on the orientation patterns of primary vascular canals relative to the long axis of the bone (Ricqles & others, 1991): 1) Laminar bone exhibits a pattern of anastomosing longitudinal canals (canals parallel to the long axis of the bone) connected by some circular canals (canals circumferentially oriented around the center of the marrow cavity); 2) Plexiform bone exhibits longitudinal and circular canals connected by radial canals (canals radiating away from the center of the marrow cavity); and 3) Reticular bone, which is characterized by regularly, but somewhat randomly oriented oblique canals. Additionally, the bone matrix is characterized by the relative orientation of collagen fibers, evidenced through the use of a polarized light microscope. A woven matrix appears isotropic under a polarized lens, indicating collagen fibers are randomly arranged. Parallel-fibered bone appears anisotropic under a polarized lens and indicates ordered and aligned fibers. 79 In an attempt to give some relative measure of growth rate between similar elements in Orodromeus, the quantitative results of Castenet and others (1996) will be adopted here and compared to histological structures seen in Dryosaurus. Dryosaurus is used here, because it too is a small ornithopod dinosaur, but more importantly, there is availability of similar-sized material for sectioning. For this purpose, a transverse cross-section of the diaphysis of several growth stages of Orodromeus and Dryosaurus femora will be documented and graphed relative to one another. Although any identical cross- section of similar bones would be useful, the circumference of the femoral shaft in bipedal animals provide direct correlative value to animal size. Dryosaurus Ontohistology Dryosaurus altus is represented in several localities from the Morrison Formation in the western United States. Two of these sites in western Colorado yield many disarticulated whole and fragmentary bones of Dryosaurus babies in ~ several growth stages (Scheetz,1991; Chure & others, 1993), permitting an unusual opportunity for an ontogenetic study of the changes in histology. Six Dryosaurus femoral shafts, measuring 2 mm in diameter to 36 mm in diameter, were thin-sectioned transversely through the diaphysis. MWC 1473 is by far the smallest femur. It consists of a 5 mm long proximal half of a left femur that would have measured, when restored, approximately 14 mm. Although the terminal head of the femur is not completely preserved, the lesser and greater trochanters remain and are defined by a 80 characteristic deep cleft between them. Just proximal to midshaft, a prominent fourth trochanter juts posteriorly. Two directional cuts for thin sections were made: a sagittal longitudinal cut through the proximal end and down through the shaft, and a transverse cross-section of the midshaft of the diaphysis. In this case, because of the incompleteness of the femur, the lowest possible cut was restricted through the shaft and fourth trochanter. The longitudinal cut reveals a thicker dense cortical layer within the diaphysis, flanking either side of a long marrow cavity. The primary cortical bone is composed of vascularized layers of longitudinal canals. The cortical bone thins high in the metaphysis up into the greater trochanter of the femur. Here, the medullary cavity is partially filled with columns of calcified hypertrophied chondrocytes. Although the head of the femur was not preserved in this specimen, another comparable embryonic femur, MWC 1420, preserves the histological structure of the distal end. This left femur measures 2.3 mm wide transversely and is internally structured with longitudinal columns of calcified cartilage within a scaffolding of thin trabecular bone. This trabecular bone extends to the terminal end of the femur. In cross-section, the diaphysis is essentially a 2 mm wide tube of compact, highly vascularized cortical bone surrounding a relatively large marrow cavity. The cortical bone matrix is isotropic under crossed nichols, indicating non-oriented collagen fibers. Random, densely distributed osteocyte lacunae occur within the bone. From the edge of the medullary cavity to the outer periosteum, the cortex is composed of six successive layers of vascular canals. 81 The inner-most layer of vascular canals open into the medullary cavity. All vascular canals appear predominantly as large, somewhat circumferentially oriented cavities, with fewer anastomosing radial and longitudinal canals. The compacta would be classified as a laminar bone type. MWC 1246 and 1254 are small femora averaging 8 mm and 10 mm, respectively, in diameter. In cross-section, the outer edge of periosteal bone traces a round- to ovoid shape, surrounding a relatively large, more circular medullary cavity. The cortex is well vascularized by longitudinal, oblique and circumferential canals within a woven matrix. From the inner portion of the cortex of MWC 1246 to the outer portion of MWC 1254, a depositional growth of three radial mm, vascular canals gradually change from predominantly oblique, to an equal proportion of oblique and circumferential canals. Accompanied by this gradual change from reticular to a more plexiform bone, is a slight posterior shift of the marrow cavity. This shift is exhibited in MWC 1254, where the medullary cavity truncates laminar bone posteriorly while having had the trailing edge filled in with endosteal bone anteriorly. The thin-section of left femur MWC 1477 is a diaphyseal cut much more elliptical in shape, both at the periosteal border and medullary border. Its average outside diameter measures 15.8 mm. The cortex is plexiform in nature, although in the anterior, or elliptical apex, the bone has fewer radial canals and is dominated by circumferential vascular canals. This cross-section has a relatively thicker cortex than smaller femora, indicating the relative rate of bone deposition exceeds medullary resorption. Although no endosteal bone has formed 82 centripetally anywhere along the cortex, the anterior and posterior expansion of the marrow cavity is evidenced by truncations of the laminar bone, especially posteriorly. A larger femur, MWC 883, is about 24 mm diameter and exhibits a similar pattern as that of the previous femur, being elliptical in form with a relatively thick cortex. In contrast to MWC 1477, dominant circumferential canals are not just limited to the elliptical ends, but are predominant within the outer half of the cortex. This vascular change is marked by a sharp line of arrested growth (LAG) (Figure 32) which measures 8.75 mm from the center of the medullary cavity. The largest Dryosaurus femur available, BYU 13312 for histological analysis is 36 mm in diameter at mid-shaft. The cross-sectional geometry is somewhat D-shaped with the flatter side medial and a rounded posterior apex. The cortical bone is for the most part plexiform, with an outer cortex sub- plexiform to laminar, characterized by less reticular canals (Figure 32). Two LAG lines are present - one averages 9.25 mm out from center, and the other, 14 mm from center. The inner LAG is truncated by a posteromedially migrated medullary cavity. Laterally, along the edge of the medullary cavity, a thin layer of endosteal bone abuts a localized portion of the inner cortex that is superimposed by multiple generations of secondary osteons. Chinsamy (1995) found no LAG lines in any of the femora of Dysalotosaurus Iettowvorbecki Virchow 1919, a dryosaurid from the Upper Jurassic Tendaguru Beds of Tanzania. Even the largest diaphyseal shaft, ~40 83 3.8 x B FIGURE 32. Dryosaurus histological thin-sections. A) Transverse section of small Dryosaurus femur, diaphysis, showing line of arrested growth (lag) in outer cortex (IVIWC 883). B) Transverse section of larger Dryosaurus femur, diaphysis, showing lag in outer cortex (BYU 13312). 84 mm in diameter, lacks an arrest line, and unlike Dryosaurus contains a dense inner cortex of primary and secondary osteons. In Dryosaurus, the laminar bone is much more vascularized by circumferential canals and the older inner cortex lacks extensive remodeling by haversion systems. Considering Dryosaurus femora reach 40 cm in length, it is likely BYU 13312 still represents an immature animal, whereas Dysalotosaurus is much closer to maturity. Heinrich and others (1993) analyzed the femoral cross-sectional geometry of a growth series of Dysalotosaurus. Among the small femoral shafts, less than 18 mm in diameter, the cortical bone is moderately thin and cylindrical with an equally circular marrow cavity. Femoral shafts over 20 mm in diameter exhibit a statistically thicker and elliptical cortex. Heinrich suggested this transition was a structural consequence due to an ontogenetic shift from quadrupedal stance to bipedality. A similar trend is found in Dryosaurus altus, with slight differences. In Dryosaurus, this transition occurs sooner, within the 10-15 mm diametrical range. The shift is marked by rapid radial growth as bone type changes from reticular to plexiform; especially along the anterior aspect of the shaft. The shaft thickens anteriorly during a posterior migration of the marrow cavity. Within the small range, bone is highly vascularized but remains predominantly longitudinal and oblique canals. This is probably due to an emphasis on longitudinal growth. 85 Orodromeus Ontohistology The smallest Orodromeus femur, MOR 968, is 15 mm long, possibly from a hatchling. Several sagittal longitudinal thin-sections of the proximal half, and transverse sections of the midshaft and were made. Like the smallest Dryosaurus femur, the longitudinal cut reveals a thicker dense cortical bone within the diaphysis, vascularized by layers of longitudinal canals. The cortical bone thins high in the metaphysis to just below the more expanded head of the femur. From within the medullary cavity of the metaphysis to the proximal end, columns of calcified cartilage are supported by thin trabecular bone (Figure 33). Like Dryosaurus, Orodromeus had well-developed joint articular ends at very early stages. The cross-section through the diaphysis is similar to the Dryosaurus embryo with notable exceptions. MOR 968 exhibits an abundance of longitudinal vascular canals in six to seven layers (Figure 33). Many of the canals within the inner cortex are primary osteons, lined with a single lamella of dense bone. The medullary cavity is located closer to the anterior edge of the shaft, but is expanding posteriorly as bone appears resorbed due to increasingly large erosion rooms. A dark peripheral cortex contrasts the lighter colored inner cortex, and may be indicative of a hatching line. Densely distributed osteocyte lacunae and abundant vascular canals indicate a rapidly growing bone, but the presence of primary osteons suggests energy and materials are expended towards mechanical strengthening of the diaphysis, as a response to loading. 86 3.8 x B FIGURE 33. Orodromeus histology of hatchling femur. A) Transverse diaphyseal cross-section of femur of hatchling (IVIOR 968). B) Longitudinal epiphyseal cross-section of femur of hatchling (IVIOR 968) showing proximal surface supported by trabecular bone (TB) and calcified cartilage (CO). 87 A 7.5 mm diameter shaft of a juvenile Orodromeus femur, MOR 407, is essentially a circular, 1.3 mm thick cortex surrounding an equally circular marrow cavity. The bone is characterized by longitudinal and oblique vascular canals I and primary osteons. The relative orientation of these canals, together with the surrounding woven matrix, suggests a “paisley-like pattern” (Figure 34). The structure is reticular bone, but it is not as highly vascularized as in Dryosaurus. Layers of vascular canals are not as distinct, although a cyclical banding of. conformable lighter laminae followed by darker laminae is observed. Four of these parasequence sets of banding occurs within the cortex. The larger of the thin-sectioned femora, PU 23443, was crushed at midshaft but would measure approximately 15 mm in diameter when restored. The femur is 15 cm long and has a glossy outer finish, unlike the mat finish observed on bones of smaller individuals. Although crushed, the transverse section through the remaining diaphysis shows the shaft to have a subrounded periphery. The cortex is relatively thicker than seen in the juvenile, and the medullary cavity has migrated slightly posterior. Longitudinal vascular canals, anastomosed by few circumferential and oblique canals, are embedded in a matrix much more parallel-fibered than the bone matrix in the juvenile (Figure 33). Primary osteons are more plentiful in the mid-cortex, and secondary osteons are common near the medullary cavity. A thin layer of dense lamellar bone of endosteal origin encircles the marrow cavity. Two distinct lines can be traced along the laminae within the cortex; one occurs near the marrow cavity, 88 8 x B FIGURE 34. Orodromeus femur histology. A) Transverse diaphyseal section of juvenile femur at mid cortex (IVIOR 407). B) Transverse diaphyseal section of near-mature Orodromeus femur showing line of changed growth (leg) in outer cortex (PU 23443). 89 5.25 mm from the femoral axis, while the other is approximately five laminae in from the periphery, 6.5 mm from center. These lines may represent lines of arrested growth. Comparative Growth Rates In an attempt to graphically illustrate the relative radial rate of bone deposition in the femoral shafts of Orodromeus and Dryosaurus, several assumptions have to be made. First, relying of the documented concommitment changes in structure and growth rate of birds and other taxa (Castenet & others, 1996; Ricqles & others, 1991), it is inferred that the similar principle holds true for dinosaurs. Bone structures related to high growth rates, are those tissues that exhibit a woven matrix of collagen fibers. Within this category, laminar bone rates the highest at a rate of over 15 microns of radial bone growth per day, followed by plexiform at 5 to 15 microns/day, and reticular bone, at a rate under 5 microns/day for the mallard duck (Castenet & others, 1996). Bone organized into parallel-fibered matrix grows at a rate 0.40 microns per day, or slower (Ricqles & others, 1991). Although this same range will be used for Orodromeus and Dryosaurus bone structures, it must be realized these numbers may not be reliable for dinosaurs, but their application is used here to illustrate differences between two dinosaur taxa. Second, it is assumed that a growth series of femora from several individuals of one taxa is representative of the typical growth within one representative individual. 90 Third, it is assumed LAG lines within the cortex of the diaphysis represents annual growth rings. This may certainly not be the case. In the cross-sections of Dryosaurus femora MWC 883 and BYU 13312, there is a discrepancy of 0.50 mm between the first LAG’S of each bone. For the purpose of simplification, 0.50 mm is considered here not significantly different given latitude for individual variation. Considering LAG’S to be annual growth rings provides a convenient reference mark. Figure 35 illustrates the relative radial growth between Orodromeus and Dryosaurus, measured along the diametrical width of the growing shaft. For a given cross-sectional width, a slope is drawn on an accumulative curve Rad ia l F em o ra l G row th Ra te of Orodromeus & Dryosaurus Shaft Diameter mm Dryosaurus Orodromeus FIGURE 35. Comparison of the rate of radial growth in the diaphysis of femora of Dryosaurus and Orodromeus, as recorded by histological structure of an ontogenetic series. 91 corresponding to the historical growth rate for the given bone type provided by each specimen. Projected lines through corresponding LAG’S may represent a year’s growth. 92 PHYLOGENY Ornithopod Classification ^ The Ornithopoda was erected by Marsh in 1895 to include bipedal, herbivorous dinosaurs with a prepubic and postpubic process, three to four functional digits on a digitigrade foot, three to five functional digits in the manus, premaxillae edentuous in the front, and solid vertebrae. Marsh included within this suborder seven families (many known from a single species): the Nanosauridae, Hypsilophodontidae, Laosauridae, Camptosauridae, lguanodontidae, Trachodontidae, and the Claodontidae. Subsequent workers have modified and added much to the ornithopod classification scheme from time to time (Le., Swinton, 1936; Romer, 1956; Steel, 1969; Galton, 1972, 1973, 1974, 1978, 1983; Molnar, 1976; Morris, 1976; Sereno, 1984, 1986; Cooper, 1985; Horner, 1990; Milner & Norman, 1984; Norman, 1984; Sues & Norman, 1990; Weishampel & Horner, 1990; Weishampel & Heinrich, 1992 ). Consistently though, the Hypsilophodontidae (small bipedal herbivorous dinosaurs), lguanodontidae (derived Iarge bipedal herbivorous dinosaurs), and the Hadrosauridae (highly specialized duck-billed dinosaurs) remain as three distinct components of the Order Ornithopoda. In attempting to situate Orodromeus into its phylogenetic context, attention was given to comparable specimens from within its least inclusive 93 group - the Hypsilophodontidae. This group has been subjected to numerous revisions since it was erected in 1882 by Dollo. Because of the often incomplete nature of material, nearly 40 taxa have been included and/or excluded into the periodically redefined family. Since its conception, the Hypsilophodontidae has matured from a phenetic "garbage can" grouping of diminutive ornithopods (Thulborn, 1971) to an evolutionary grade from which several iguanodontians independently arose (Galton, 1973, 1974a, 1974b, 1980), to a monophyletic plexus (Sereno, 1986; Sues & Norman, 1990; Norman, 1990), and finally to the recent status as a cohesive monophyletic group of four clades (Weishampel & Heinrich, 1992) (Figure 36). Although the recent cladistic analyses are the best critiques on hypsilophodont phytogeny thus far, at least 3 anomalies appear. The first apparent anomaly within the Hypsilophodontidae, as pointed out by Weishampel and Heinrich (1992), is the mid-Jurassic lineage divergence of the Maastrichtian dinosaur Thescelosaurus] a 105 million year minimal divergence time. This represents the highest divergence time among all the Dinosauria, and was proposed as indicative of the large number of taxa missing from the fossil record. The second anomaly is the systematic position of the Lower Cretaceous Tenontosaurus within the basal lguanodontia. The ambiguity of Tenontosaurus lies in the four synapomorphies with Hypsilophodontidae (Weishampel & Heinrich, 1992). Norman (1990) points out 7 characters that group Tenontosaurus with hypsilophodonts and discusses many of the 14 characters 94 A) Gallon (1971) suggested a hypsilophodontid-grade from which several lines of derived ornithopods arose. B) Weishampel and Heinrich (1995) suggested the Hypsilophodontidae (node 1) constitutes a monophyletic group. Fossil record for basal ornithopods indicated b y _____ ; no fossil record indicated b y .............; postulated relationships indicated b y ............... Key to abbreviations is given in List of Nomenclature. 95 used by Sereno (1986) to group Tenontosaurus with Iguanodontia as allometric convergence. Third, although Orodromeus clades with many derived hypsilophodonts, it possesses many primitive characters which are ignored in cladistic analysis (i.e. fabrosaurid dentition and occlusion, jugal boss, general fore and hind limb morphology). Retention of, or reversion to, primitive characters is unexpected in Upper Cretaceous taxa. ;! A thorough descriptive character list of Orodromeus, together with taxa not previously included in phylogenetic analysis is used here in a cladistic i 'i attempt to test proposed phytogenies and resolve some of these anomalies. Methods , Preliminary analysis of 85 characters across 15 taxa, including sister group taxa of the Fabrosaurid grade and out-group taxa of the Iguanodontian grade, failed to verify a monophyletic hypothesis for the Hypsilophodontidae. A more taxa-extensive and character-extensive analysis was required to locate possible monophyletic clades and to better define small ornithopod dinosaurs. A check-list of 558 variable morphologic features across nearly every ; skeletal element was compiled and used to evaluate taxa. Actual specimens were evaluated when available, supplemented by key references. When I specimens were unavailable, published descriptions, photographs and illustrations of specimens were relied on (see Appendix B). Because a large degree of missing data inflicts ambiguity in the relative placement of some taxa, (i .'i 96 taxa based on very limited material were not included in the cladistic analysis. All morphological checklists of each taxon were compiled into a description summary and each point of variation evaluated on its distribution across taxa to determine autapomorphic (characters unique to a taxon), sympliesiomorphic (shared primitive characters), and synapomorphic conditions (shared derived characters). Autapomorphies diagnose a taxon, providing an identity that sets one taxon apart from other taxa (see Appendix C). Because phylogenetic analyses rely on the “nest-ability” of characters, autapomorphies are seldom, if ever, listed in phylogenies because they lack the ability to group the character with any other. However, autapomorphies should be listed as an addendum to phylogenies, as their importance as potential shared derived characters has been overlooked. The potential for an autapomorphy to turn into a shared derived character is especially evident for paleontology, as new taxa are continually discovered, reference to autapomorphy lists may provide links to potential relationships (see Appendix C). Shared characters, on the other hand, allows for grouping and can specify the inclusion or exclusion of taxa with/from one another. Initially, all characters used in this study were assumed apomorphic if any two taxa share a similar feature. The initial apomorphy list was culled of characters that appeared as having no phylogenetic value, showing up intermittently in taxa throughout the fabrosaurid, hypsilophodontid and iguanodontid grades. The remaining characters were assigned numerical values and scored binary, when defined as present (1) or absent (O), or defined sequentially, when multiple character states 97 existed. Numerical values of an initial 221 characters were compiled in a data matrix using MacCIade version 3.03 (Maddison & Maddison, 1992) and analyzed using PAUP, version 3.0 (Phylogenetic Analysis Using Parsimony, Swofford, 1990)(see Appendix C). In an attempt to minimize prior assumptions, trees were generated unrooted and all data were run unordered and given equal weight. Based on phytogenies proposed by previous workers (Weishampel & Heinrich, 1992; Sereno, 1986; Norman, 1990) and preliminary analyses run for this study, characters and character states common among the sister-group dinosaurs were considered sympliesiomorphic, or the primitive state. As the established sister group to the remaining Ornithopoda (Weishampel, 1990; Weishampel & Witmer, 1990; Weishampel & Heinrich, 1992), heterodontosaurs are represented mostly by fragmentary material from about a half dozen taxa. Heterodontosaurus, however, is represented by two complete skulls and a complete skeleton (Weishampel & Witmer, 1990). Using a single taxa to represent a sister group would complicate defining character polarity if the taxon possesses uniquely derived characters that mask the primitive condition. For this reason, two primitive outgroup taxa and one sister- group taxon were analyzed, representing basal thyreophorans (ScutelIosaurus), fabrosaurids (Lesothosaurus), and heterodontosaurs (Heterodontosaurus). Similarly, many derived outgroup taxa of the iguanodontid grade were utilized beyond the recognized basal iguanodont Dryosaurus. This was done to trace a character over several taxa, to understand trends and define 98 synapomorphies and transformation series suggested by multiple character states. Several refining cladistic analyses culled phylogenetically uninformative characters of 19 taxa, generating a finalized tree on 124 characters, each polarized a posteriori where possible. Three equally parsimonious trees were identified using PAUP’s Heuristic search methods. In an attempt to resolve these options into a more precise cladogram, a more extensive search was performed using the exact Branch-and-Bound methods. Identical results occurred and were summarized into a strict consensus tree (Figure 2), Many taxa based on fragmentary material were not included in the cladistic analysis because of the problems created by missing data. A phytogeny based on taxa with substantial morphologic characters allows for a more accurate framework. This framework will allow workers to assess the phylogenetic context of additional taxa, or taxa known from insufficient material. One of the most evident constructs of the cladogram is the dissolution of the “Hypsilophodontidae” into an essentially pectinate cladogram with few dual- taxa clades. Tenontosaurus nestles solidly within a phylogenetic context between the hypsilophodontid grade and the iguanodontid grade ornithopods, settling the ambiguity of its placement. The relationships within the Agilisaurus-Yandusaurus-Othnielia clade remain unresolved. PAUP treats Agilisaums equally as a sister taxa, and in­ group taxa, or an outgroup taxa to the Yandusaurus-Othnielia clade - likely a 99 result from having to rely on Chinese literature. Zephyrosaurus and Orodromeus form a monophyletic group as proposed by Weishampel & Heinrich (1992), as well as Dryosaurus-Dysalotosaurus. Winkler and others (1997) demonstrated a tight relationship between Tenontosaurus tilIeti and T. dossi, although, only T. tilleti was included in analysis here. Similarly, the relationship between Iguanodon atherfieldensis Hooley 1925 and I. bernissartensis Boulenger 1881 has been thoroughly demonstrated by Norman (1986). Iguanodon atherfieldensis was used here and relationships within the clade were not tested. Many small ornithopod taxa are not included in this study. Unnamed taxa, taxa currently being studied by other workers, and taxa based on fragmentary material were not available for a character analysis. Taxa based on limited material are not conducive for building a cladistic framework around and tend to clutter the analysis. For example, the inclusion of Valdosaurus, which is based on fragmentary material (Galton, 1975, 1977; Galton & Taquet, 1982), internally collapses the dryosaur clade. Additional material, minimizing missing data would control these factors. Additional cranial material for Othnielia and DrinkernistiwW no doubt help to get a clearer understanding of the relationships of all North. American primitive ornithopods. Othnielia and Drinkerare both found from the Upper Jurassic Morrison Formation. Thus far, they are differentiated based on the presence or absence of accessory cusps on denticles of cheek teeth (Bakker & others, IOO 1990). Unfortunately, the type specimen of Othnielia rex (Marsh) is a juvenile femur (YPM 1915), named Nanosaurus rex by Marsh in 1877, but renamed by Galton (1977) one hundred years later because the type species for the genus Nanosaurus (N. agilis, YPM 1913) is an indeterminate specimen of bone fragments, with teeth and bone impressions in sandstone. Dentary and maxillary teeth recovered from the same quarry as the Othnielia rex type specimen were subsequently assigned as topotypes (Bakker and others, 1990). Other equally small ornithopods collected from the Morrison Formation of Wyoming had femora of similar form as Othnielia but the cheek teeth differed from Othnielia topotype specimens. As more material comes to light, these two genera may show significant differences. The teeth however, do not constitute a valid character, as a small dentary collected by Felch in 1886 from the Morrison Formation of Canon City, Colorado (USNM 5829) retains both types of teeth (Figure 39). If Drinker and Othnielia are eventually shown to be two distinctly different dinosaurs, but not differentiated on femora, then Othnielia rex (type species for the genus) becomes a nomen nudum. Results Character Summary Many evolutionary changes occurred within ornithopod taxa in the 40 million years from the little Agilisaurus to the large lguanodon. Most changes 101 I cm FIGURE 37. Othneilia rex dentary teeth. A) Left dentary in medial view showing relative position of teeth (USNM 5829). B) Close-up of posterior-most tooth with accessory cusps on denticles similar to that described for Drinker nisti. C) Close-up of tooth with smooth denticles typical of teeth described for Othneilia rex (USNM 5829). can be attributed to more efficient herbivorous adaptations and an increase in size. Within the skull, the pterygoid wing reduces in size and arises lower off a more vertically oriented quadrate and a quadrate notch develops within a shorter jugal wing instead of the quadratojugal. The quadratojugal is much reduced and 1 0 2 meets the quadrate high above the articular jaw joint. A robust postorbital develops. Frontals flatten, shorten and participates little in the orbit. Nasals lengthen and migrate posteriorly. Loss of teeth in premaxilla which becomes broader and longer on the posterior process which rides posteriorly within a sulcus of lengthened maxilla packed with teeth creating a continuous occlusal surface. Teeth, become high crowned, diamond-shaped, Iingually convex, lose cingulum and crowns taper to root. Enamel thins on one side. The anterior tip of the longer, transversely thicker dentary migrates low, supporting a predentary from below. Predentary forms forked or dual ventral processes. Teeth become high lozenge-shaped crowns with a posteriorly set apical ridge. Primary, secondary and tertiary ridging occurs on the thickly enameled side of the teeth and many denticles are not supported by ridges. Tooth roots taper from crowns, are curved, squared in cross-section and grooved along their sides from close- packed neighboring teeth. The post-coronoid elements of the Iowerjaw shorten and become steeply concave in lateral view. The back of the skull bears a reduced smooth supraoccipital but overly-sized paraoccipital processes. The exoccipital doesn’t participate with the large occipital condyle. The floor of the braincase upon the basioccipital bears a median ridge. Postcranially, cervical vertebrae become opisthocoelous, with a spine centered over the centrum. A transition from forward-pivoting ribs to outward- pivoting ribs occurs more posteriorly on the rib-cage. One or more dorsal vertebrae are added, as well as another sacral vertebra. Sacral vertebral spines are longer and lean somewhat anteriorly. The coracoids reduce in length with a 103 / coracoid foramen open to the scapular facet. Sternals become hatchet-shaped with long ventrolateral processes. The ulnae possess a higher olecranon process and the shafts are cylindrical. The carpus becomes fused and the manus loses phalanges on digits III, IV, and V. Longer manus develops with hoof-like unguals. The ilium is vertically broader on the posterior end and the pubic and ischiatic peduncles are short. The anterior ramus of the pubis is vertically broad and flattened transversely. An additional support to the pubis is provided by a sacral rib. The posterior process of the pubis is reduced. Ischia bear larger and stronger iliac peduncles and have proximally placed obturator processes and the bar-like shafts end in a foot. The femora become straighter, with a lower fourth trochanter. Distally, the femur bears a pronounced anterior intercondylar groove. The lateral posterior condyle is much reduced and the medial condyle expanded. Tibia length reduces to near femur length and the proximal condyles are separated by a broad groove. Astragalus tends higher posteriorly and lower anteriorly. In dorsal view, the medial tarsal is round and the lateral tarsal is reniform in shape. Shortened and robust feet are comprised of the central three digits, pes digits I and V are lost or nonfunctional. Unguals hoof-like. Evolutionary Trends A major evolutionary trend exhibited through the small ornithopod grade is the transition from insectivorous fabrosaurs, through the step-wise improvements in herbivory of ornithopods. Wing & Tiffney (1987) and Bakker (1978) suggested 104 the increased diversity and abundance of the low-browsing ornithopod dinosaurs in the mid and Late Cretaceous was a reciprocal interaction with angiosperms, analogous to the coevolution between grazing ungulates and grasses described by McNaughton (1984). Although there are many converging adaptive traits found in ornithopod dinosaurs and ungulates, the phylogenetics of ornithopod dinosaurs indicates many of the major masticatory improvements were set in place prior to the development of angiosperms. These major changes have culminated by the Upper Jurassic in the form of Camptosaurus. The earliest unequivocal angiosperm pollen occurs from the Valanginian of the Early Cretaceous (Crane and others, 1995), and by Late Albian, angiosperms displaced gymnosperms as the dominant land plant in lowland environments (Crabtree, 1987). The first significant improvement in ornithopods is a switch from a shear- dominated occlusion, to a translational, compressive force. This is achieved in Heterodontosaurus through a slight medial rotation of the mandibles (Weishampel, 1984a; Norman & Weishampel, 1985; Crompton & Attridge, 1986). Early in ornithopods, a pleurokinetic skull is developed and translation occurs with the upper jaws rotating when the lower jaw is fully adducted (Weishampel, 1984a; Norman, 1984b; Norman & Weishampel, 1985). Other improvements are analogous to many of the mammalian herbivorous adaptations listed by Rensberger (1986) (see Table 2). An increased chewing surface and flatter chewing area provided an increased mechanical ability. A stronger enamel develops, becoming disproportionately 105 thicker Iingualiy on dentary teeth, and Iabially in maxillary teeth. Animals increased in size with a higher posterior skull region. Jaws lengthen, a taller coronoid develops, and a steep surangular suggests increased efficiency of larger chewing muscles. Improvements in translational efficiency is found in the first hadrosaurs by the Cenomanian. In hadrosaurs, rows of hypsodont teeth created multiple cutting blades, analogous to the enfolding of enamel in ungulate mammals. TABLE 2. TRANSITIONAL CHANGES FOR EFFICIENT HERBIVORY Internode Ornithopod Change Mammalian Change Rensberger (1986) 2 -Maxillary and dentary teeth packed (reversed in Orodromeus) -Development of cheeks 3 -Anterior dentary tip lower, increasing support for predentary -Dentary arched medially 4 -Anterior dentary tip lower, increasing support for predentary 5 -Jugal wing and quadratojugal high above distal end of quadrate -Quadratojugal foramen -Post coronoid elements of the jaw shorten —Flatter chewing surfaces.( In Protungulatum, the occlusal angle measured from vertical is 40 & 55 degrees) Animals increase in size 6 -Curved maxillary roots -Maxillary crowns Iingually concave 7 -Continuous occlusal surface across cheek teeth -Dentary teeth with primary, secondary and tertiary ridges —Increased chewing surface area 106 TABLE 2. TRANSITIONAL CHANGES FOR EFFICIENT HERBIVORY 8 -Maxillary teeth with tapering roots, lacking a distinct neck between the crown and root -Enamel thickened on labial side maxillary crowns, and thinned on lingual -R idging on lingual side dentary crowns —Enamel thickened on lingual side dentary crowns and thinned on labial -O n ly few denticles supported by ridges -Curved dentary tooth roots —Stronger enamel —Enamel tends to become relatively thin in translational systems that are highly lophodont. —Heavier cusps to withstand higher compressive stress 9 -N o cingulum on maxillary teeth 10 -N o cingulum on dentary teeth -Lozenge-shaped dent crowns -BiIobed predentary —High cheek teeth —A high rate of wear selects for hypsodont teeth, which tend to have parallel sides to maintain its shape during growth and wear. 11 -SuranguIar concave 12 -PM sulcus on maxilla -H igh diamond-shaped crowns max -Pos t apex dent -Dentary teeth with 3 ridge types —Random directionality in enamel edges and expanded cusps 13 -Dentary tip low (stage 3) -Dentary roots squared(stage 4) -Postcoronoid short(stage 2) —Animals increase in size REFERENCES CITED 108 REFERENCES CITED Amprino, R. 1947. 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APPENDICES 1 2 2 APPENDIX A Orodromeus Specimens Studied 123 ORODROM EUS CRA N IA L ELEM ENTS STU D IED Premaxilla NDOR 4 3 6 ,6 1 3 ,6 2 3 2 specimens unnumbered Maxilla M OR 2 9 4 ,4 3 6 ,6 1 3 3 specimens unnumbered Nasal MOR 473 Frontal M OR 2 4 8 ,2 9 4 , 436, 623 3 specimens unnumbered Parietal MOR 294, 473 Postorbital NDOR2 9 4 ,4 3 6 ,4 7 3 3 specimens unnumbered Squamosal MOR 248, 294 I specimens unnumbered Quadrate M 0 R 2 4 8 ,2 9 4 ,4 3 6 , 6 1 3 ,6 2 3 ,6 4 7 2 specimens unnumbered Quadratojugal M OR 2 4 8 ,2 9 4 Jugal M 0 R 2 9 4 ,4 3 6 ,6 1 3 ,6 4 7 3 specimens unnumbered Lacrimal MOR 623 I specimen unnumbered Prefrontal MOR 294, 473 I specimen unnumbered Supraorbital M 0 R 2 9 4 623 647 I specimen unnumbered Laterosphenoid MOR 473 I specimen unnumbered Opisthotic M O R 2 9 4 ,4 0 1 ,4 0 3 ,4 3 6 ,4 7 3 ,6 2 3 6 specimens unnumbered Prootic M O R 2 9 4 ,4 0 3 ,4 3 6 ,4 7 3 Supraoccipital M O R 2 9 4 ,4 0 3 ,4 7 3 Basioccipital M O R 3 5 0 ,4 0 3 ,4 3 6 ,4 7 3 ,6 1 3 ,7 0 5 124 ORODROMEUS C R A N IA L ELEM ENTS STU DIED Basisphenoid MOR 294, 403, 473, 623 Dentary M O R 2 4 8 ,2 5 3 ,2 9 4 ,4 3 6 ,6 1 3 ,6 4 7 PU 23247 3 specimens unnumbered Surangular5 Angular, articular MOR 2 9 4 ,4 3 6 I specimens unnumbered ORODROMEUS A X IA L ELEM ENTS STUDIED Atlas MOR 473 ,613 7 specimens unnumbered Axis MOR 473 Cervical Vertebrae M 0 R 2 5 3 ,2 5 4 ,2 9 4 ,4 3 6 ,4 7 3 ,6 1 3 ,6 2 3 ,6 4 7 ,6 6 1 PU 2 3 2 4 8 ,2 3 3 4 6 ,2 3 4 0 8 2 specimens unnumbered Dorsal Vertebrae M O R 2 5 1 ,2 5 3 ,2 9 4 ,3 3 1 ,4 0 1 ,4 1 1 ,4 3 6 ,4 7 3 ,5 2 8 ,5 3 0 ,6 1 3 , 623,647,661. 685 PU 2 2 4 1 2 ,2 2 6 0 3 ,2 3 2 4 8 ,2 3 4 0 8 ,2 3 4 0 9 .2 3 4 3 1 ,2 3 4 3 2 , 23443 21 specimens unnumbered Rib M O R 2 3 8 ,3 3 1 ,4 0 1 ,4 3 6 , 4 7 3 ,6 2 3 ,6 6 1 PU 23346,23431 9 specimens unnumbered Caudal Vertebrae M O R 2 3 8 ,2 5 2 ,2 5 6 ,2 9 4 ,4 3 6 ,4 7 3 ,6 1 3 ,6 2 3 ,6 4 7 ,6 6 1 | PU 2 2 4 1 2 ,2 3 2 4 8 ,2 3 3 4 6 ,2 3 4 0 9 ,2 3 4 3 1 ,2 3 4 3 2 ,2 3 4 4 2 10 specimens unnumbered Chevron M O R 2 3 8 ,2 5 2 ,3 3 1 ,4 3 6 ,6 2 3 ,6 4 7 8 specimens unnumbered 125 ORODROMEUS FO RE LIM B ELEM EN TS STUDIED Scapula MOR 2 5 3 ,2 5 6 ,2 9 4 ,4 3 6 ,4 7 3 ,5 2 8 ,6 1 3 ,6 2 3 ,6 4 7 ,6 6 1 PU 2 3 3 4 6 ,2 3 4 3 1 ,2 3 4 4 2 ,2 3 4 4 3 ,2 2 4 4 5 6 specimens unnumbered Coracoid MOR 27 2 ,2 9 4 , 623, 647, 944 PU 23442 I specimens unnumbered Sternal MOR 623 Humerus M 0 R 2 4 8 ,2 5 7 ,2 9 4 ,4 0 4 ,4 3 6 ,4 7 3 ,6 1 3 ,6 2 3 .6 4 7 ,6 6 1 PU 2 2 4 4 5 ,2 3 3 4 6 ,2 3 4 0 8 ,2 3 4 3 2 2 specimens unnumbered Ulna M 0 R 2 4 8 ,2 9 4 ,4 7 3 ,6 2 3 ,6 6 1 I specimens unnumbered Radius M O R 2 4 8 ,2 9 4 ,4 7 3 ,6 2 3 ,6 4 7 4 specimens unnumbered Manus PU 23442 2 specimens unnumbered ORODROMEUS PELV IC ELEM EN TS STUDIED Ilium N 4 0 R 2 3 8 ,2 5 1 ,2 9 4 ,3 3 1 ,4 0 1 ,4 1 0 ,4 3 6 ,4 7 3 .5 3 0 ,6 1 3 ,6 4 7 , 661 PU 2 2 4 1 2 ,2 2 4 1 2 ,2 2 4 4 5 , 23257,23408 2 specimens unnumbered Ischium N 4 0 R 2 3 8 ,2 5 1 ,2 9 4 ,4 1 0 ,4 1 2 ,4 3 6 ,4 7 3 ,6 1 3 ,6 6 1 PU 22412, 23346, 23431 Pubis MOR 410, 473,705 PU 22412, 23431,23442 3 specimens unnumbered 126 ORODROMEUS HIND LIM B ELEM EN TS STU DIED Femur M 0 R 2 3 8 ,2 4 8 ,2 5 2 ,2 5 5 ,2 9 4 ,3 3 1 ,3 5 0 ,4 0 5 ,4 0 7 ,4 3 6 ,4 7 3 , 5 3 0 ,5 5 4 ,6 1 3 ,6 2 3 ,6 4 7 ,6 6 1 ,6 8 5 PU 2 2 4 1 2 ,2 2 4 4 0 ,2 2 4 4 5 ,2 2 5 8 7 ,2 3 2 4 8 ,2 3 4 0 8 ,2 3 4 0 9 , 23432,23443 10 specimens unnumbered Tibia M O R 2 3 8 ,2 4 8 ,2 5 2 ,2 5 3 ,2 9 4 ,3 5 0 ,4 1 0 ,4 3 6 ,4 7 3 ,5 2 8 ,5 3 0 , 5 3 3 ,5 5 4 ,6 1 3 ,6 2 3 ,6 4 7 ,6 6 1 PU 2 2 4 1 2 ,2 2 4 4 5 ,2 3 2 4 8 ,2 3 2 5 0 ,2 3 3 4 6 ,2 3 4 0 8 ,2 3 4 0 9 , ' 23432 15 specimens unnumbered Fibula N 4 0 R 2 3 8 ,2 4 8 .3 3 1 ,4 3 6 ,5 3 0 ,6 1 3 ,6 2 3 ,6 6 1 PU 2 2 4 1 2 ,2 2 4 4 5 .2 3 3 4 6 ,2 3 4 0 8 ,2 3 4 3 2 4 specimens unnumbered Astragalus & 4 0R 248 ,2 9 4 ,3 3 1 ,3 5 0 ,4 7 3 ,5 3 0 ,6 1 3 ,6 2 3 PU 2 2 4 4 5 ,2 3 3 4 6 ,2 3 4 0 8 ,2 3 4 0 9 ,2 3 4 3 2 3 specimens unnumbered Calcaneum M O R 2 3 8 ,2 9 4 ,3 3 1 ,4 7 3 ,5 3 0 ,6 2 3 ,6 6 1 PU 2 3346 ,23408 ,23409 6 specimens unnumbered Tarsal M O R 2 4 8 ,4 7 3 ,5 3 0 ,6 2 3 ,6 6 1 PU 23346,23432 7 specimens unnumbered Metatarsal M O R 2 4 8 ,2 5 1 ,2 5 6 ,2 9 4 ,3 3 1 ,3 5 0 ,4 0 2 ,4 3 6 ,4 7 3 ,5 2 8 ,5 3 0 , 5 5 4 ,6 1 3 ,6 2 3 ,6 4 7 ,6 6 1 PU 2 2 4 1 2 ,2 2 4 4 5 ,2 3 2 4 8 ,2 3 3 4 6 ,2 3 4 0 8 ,2 3 4 0 9 ,2 3 4 3 1 , 23432 11 specimens unnumbered I127 ORODROMEUS HIND LIM B ELEM ENTS STU D IED Phalanges M 0 R 2 4 8 ,3 3 1 ,4 3 6 ,4 7 3 ,5 2 8 ,5 3 0 ,6 2 3 ,6 4 7 ,6 6 1 PU 2 2 4 1 2 ,2 2 4 4 5 ,2 3 2 4 7 ,2 3 3 4 6 ,2 3 4 0 8 ,2 3 4 3 1 ,2 3 4 3 2 , 23443 11 specimens unnumbered Ungual M O R 2 4 8 ,3 3 1 ,4 3 6 ,4 7 3 ,6 1 3 ,6 2 3 ,6 6 1 PU 2 2 4 1 2 ,2 2 4 4 5 ,2 3 2 4 7 ,2 3 3 4 6 ,2 3 4 3 1 ,2 3 4 3 2 10 specimens unnumbered 128 APPENDIX B Taxa, Specimens, & References used for Phylogenetic Study 129 SPECIMENS AND R E F # # m # E D # fM IS # T U m : J ' : # Scutellosaurus Iawleri Colbert, 1981 MNA P1.175 Colbert, 1981 Lesothosaurus diagnosticus Gallon, 1978 —Fabrosaurus australis Ginsburg, 1964 BMNH RUB17, RUB23, R1102, R1103, R1104, R8501, 11956; SAM K400, K401, K1106; MNHN LES9 Gallon, 1978; Crompton, 1968; Thulborn, 1970, 1971, 1972; Crompton & Attridge, 1986; Santa Luca, 1984; Sereno, 1991; Gow, 1981; Weishampel, 1984 Agilisaurus Iouderbacki He, 1979 ZDM 6011 Peng, 1992 Yandusaurus hongheensis He, 1979 — Y. multidens He & Cal, 1983 T 6001, 6002 He, 1979; He & Cai, 1983, 1984 Othniella rex (Marsh) 1877 -1894, Laosaurus consors Marsh — 1878, Laosaurus gracilis Marsh — 1877, Nanosaurus rex Marsh -1977, Othnielia rex (Marsh) Gallon -1990, Drinker nisti Bakker, Gallon, Seigwarth & Filla YPM 1882, 1915, 9524; BYU ESM-163R; USNM 5808, 5829, 8397; MWC 1460; CPS 106, 107, 108,109, 197, 198 Galton, 1977, 1980; Dodson and others, 1980; Galton & Jensen, 1,973a; Marsh, 1877; Bakker, Galton, Seigwarth & Filla, 1990 130 SPEC IME# AND REFERENCES USED IN THIS STUDY. • . . • : ■ • ■ • •• . ' v:’ • ' Camptosaurus dispar Marsh, 1879 -1879, Camptonotus dispar Marsh -1879, Camptonotus amplus Marsh -1885, Camptosaurus dispar (Marsh) Marsh -1885, Camptosaurus amplus (Marsh) Marsh -1894, Camptosaurus medius Marsh -1894, Camptosaurus nanus Marsh -1909, Camptosaurus browni Gilmore YPM 1877, 1878, 1880, 1887; USNM 2210, 5820 Gilmore, 1909; Norman, 1986; Gilmore, 1924 Hypsilophodon foxii Huxley, 1869 BMNH R197, R192, R193, R194, R2477 Gallon, 1974b; Norman, 1986; Huxley, 1869; Gallon, 1981 “Proctor Lake Hypsilophodont” Winker and others, 1988 SMU unnumbered Winker and others, 1988 Zephyrosaurus schaafi Sues, 1980 — 1979, ? Hypsiiophodon weilandi Galton & Jensen MCZ 4392; MOR 759 Sues, 1980; Ostrom, 1970; Galton & Jensen, 1979 Tenontosaurus tilletti Ostrom, 1970 MCZ 4205; YPM 5456; AMNH 3061,3031 Winkler, Murry & Jacobs, 1997; Dodson, 1980; Forster, 1990; Ostrom, 1970 131 SPECIMENS ANDkREFERENCES USED IN THIS STUDY VaIdosaurus canaliculatus Gallon, 1975a -1975a, Dryosaurus? canaliculatus Gallon -1980, Valdosaurus canaliculatus (Gallon) Gallon BM R170, R180, R184, R185, BMNH R2150, 2183, 2459, R5849, R8420, R8421, R8670, 28697, 36509 Lydekker, 1888; Gallon, 1975a, 1975b, 1980; Norman, 1977, 1990; Gallon & Taquet, 1982 Fulgurotherium australe von Huene, 1932 BMNH R3719; QM F10220, F10221, F12673, F66764; AM F6671, F66765, F66767, F66775 Molnar & Gallon, 1986; Molnar, 1980; Huene, 1932 Orodromeus makelai Horner & Weishampel, 1988 -1924, Laosaurus minimus Gilmore See Tables Russell, 1949; Horner & Weishampel,1988; Weishampel & Weishampel, 1983; Gilmore, 1924; Horner & Weishampel, 1988 Thescelosaurus neglectus Gilmore, 1913 — 1940, T. edmontonensis Sternberg SMNH P1225; AMHN 117, 973, 5889, 5891, 5034; NMC 5031, 8537; CM 9900, 38327; LACM 33543; USNM 7757, 7758, 7760, 7761 Russell, 1964; Sahni, 1972; Cobban & Reeside, 1952; Carpenter, 1979; Estes, 1964; Estes Berberian & Meszoely, 1969; Gallon, 1974a; Gilmore, 1913, 1915,1920; Lupton Gabriel & ■ West, 1980; Morris, 1976; Sternberg, 1940 132 -SliIcJMlks aM Parksosaurus warreni (Parks, 1926) Gallon — 1926, Thescelosaurus warreni Parks ROM 804 Parks, 1926; Gallon, 1973; Sternberg, 1937; Fox, 1978 Bugenasaura infernalis Gallon, 1995 SDSM 7210; MOR 979 Morris, 1976; Gallon, 1995 -1976, Thescelosaurus sp. Morris Heterodontosaurus tuck! Crompton & Charig, 1962 SAM K1332 Santa Luca, 1980 Iguanodon atherfieldensis Hooley, 1925 BMNH R754, R5764; IRSNB 1551 Norman, 1986, 1987 -1832, I. mantelli Meyer -1850, Heterosaurus neocmiensis Cornuel -1879, Vectisaurus va Ide ns is Hulke -1888, Sphenospondylus gracilis Lydekker Rhabdodon priscus Matheron, 1869 -1881 Mochlodon Seeley -1871 Iguanodonsuessi Bunzel -1881 Oligosaurusadelus Seeley -1881 Ornithomerus gracilis Seeley -1900 Mochlodon robustus Nopcsa -1900 Camptosaurus inkeyi Nopcsa -1902 Onychosaurus hungaricus Nopcsa BMNH R3389, R3393 thru R3396; R3398; R3402; R3411; R4901; R4916; R5491 Gilmore, 1909; Nopcsa, 1900; Weishampel, Grigorescu & Norman, 1991; 133 SPECIMENS A N D # F m N # # # ; ,N : - r H lS STUDY Dryosaurus altus (Marsh, 1878) Marsh - 1878, Laosaurus altus Marsh YPM 1876; USNM 5826, 5830; AMNH 834, 5781; CM 1949, 3392, 11340, 41687; MWC 1200- 1286 and 1360-1422 Galton1 1977a, 1977b, 1980, 1983; Gilmore, 1925 Dysalotosaurus Iettow- vorbecki Virchow, 1919 ~ 1977, Dryosaurus Iettowvorbecki (Virchow) Gallon HMN specimens: dy I through dy VI, dy A, dy B, wj945, wj9027, wj5840, mbr1412, mbr1480, mbr1487, mbr1540, mbr1579, mbr1585, Janensch, 1955; Heinrich & Weishampel, 1993; Chinsamy, 1995; Gallon, 1977a Gasparinisaura cincosaltensis Coria & Salgado, 1996 MUCPv 208, 212 to 218, 225 to 227; MCS 1, 2 , 3 Coria & Salgado, 1996; Salgado & others, 1997 Ouranosaurus nigeriensis Taquet, 1976 GDF specimens: 300, 301, 302, 381 Taquet, 1976 134 APPENDIX C Phylogenetic Analysis \ 135 Tree length = 357 Consistency index (C l) = 0.487 Homoplasy index (H I) = 0.513 Cl excluding uninformative characters = 0.486 HI excluding uninformative characters = 0.514 Retention index (R I) = 0.671 Rescaled consistency index (RC) = 0.327 — 38 — 36 —35 ----34 ■21 L r -22 I ScutelIosaurus Lesothosaurus Heterodon tosauru A g ilisaurus Vandusaurus O tn ie lia Zephyrosaurus Orodromeus ThesceIosaurus Parksosaurus Bugenosaurua Hypsilophodon Gasparinisaura Tenontosaurus Rhabdodon Oryosaurus Dysalotosaurus Camptosaurus Iguanodon Ouranosaurus One of three most parsimonious cladograms of basal ornithopod phylogeny based on 124 characters using PAUP 3.0. A listing of shared derived characters for each of the numbered nodes begins on page 137, followed by explanations of characters. 136 Tree length = 357 Consistency index (C l) = 0.487 Homoplasy index (H I) = 0.513 Cl excluding uninformative characters = 0.486 HI excluding uninformative characters = 0.514 Retention index (R I) = 0.671 Rescaled consistency index (RC) = 0.327 Scutellosaurus — Lesothosaurus ---- Heterodontosauru L —34 Agilisaurus Vandusaurus Otn ie lia I---- Zephyrosaurus Orodromeus — Thescelosaurus Parksosaurus U r Bugenosaurua L Hypsilophodbn Gasparinisaura ---- Tenontosaurus L Rhabdodon -27 r — 26 •25 L — Dryosaurus Dysalotosaurus Camptosaurus r— Iguanodon -24 1------ Ouranosaurus Same phylogeny from page 135 depicted in a phylogram. Branch lengths determined on relative number of acquired and/or reversed apomorphies. A listing of shared derived characters for each of the numbered nodes begins on page 137, followed by explanations of characters. 137 Apomorphy lis ts : Branch Scutellosaurus <-> node_3S' node^SS —> node_37 node_37 — > Heterodontosauru Q node_J37 —> node_36 node_36 —> Aqilisaurus Character Steps Cl Change SS.pst apex o I 0..333 0 < -> I 9 6 .loss of ph I 0..667 0 < = > I 103.large i l ia I 0..250 I < = > 0 I 10.anterior i I 0.,500 I < = > 0 25 .long nasal I I. ,000 I ---> 2 29.recessed p I 0. 500 0 ---> I 31 .packed max I 0. 200 0 ---> I 32 .cheek teet I I . 000 0 = => I 63.narrow den I 0. 333 0 ---> I 71 .small fora I 0. 500 I ---> 2 96 .loss of ph I 0. 667 I 2 99 .ischiac pe I I . 000 0 ---> I 108.Lesser Ia t I I . 000 0 I 112.proximal b I 0. 429 I ---> 2 120.calcaneum I 0. 500 0 ---> I 30 .premax con I 0. 333 0 I 35.maxi I Iary I 0. 500 0 I 36.continuous I 0. 500 0 I 38.pst apex o I 0. 333 I ---> 0 4 4 .i uqal boss I 0. 500 0 I 54.ridging on I 0. 500 0 I 55 .enamel one I 0. 500 0 = => I 57.no cingulu I 0. 500 0 I 58.dentary ro I 0. 429 I = => 2 81.5-6 sacral I 0. 500 2 ==> I 93.high olecr 2 0. 333 0 2 101.d is ta l foo I 0. 500 0 I I 2I . round medi I 0. 500 I = => 0 27.5 or less I 0. 667 0 = => I 28 .everted ma I 0. 286 0 = => I 4 2 .i uqal not I 0. 333 0 = => I 43.slender ju I 0. 500 0 ---> I 4 9 .i uqal form I 0. 333 0 I 5 0 .i uqal touc I 0. 500 2 I 51 .dentary t i I 0. 667 0 ---> I 6I . dentary ar I 0. 333 0 ---> I 65.no mandibu I I . 000 0 I 74.BO tubera I 0. 333 0 ---> I 80.16 or more I 0. 600 0 ---> I 85.caudal rib I I . 000 0 ---> I 88.caudal spi I I . 000 0 ---> I 9 6 .loss of ph I 0. 667 2 ---> 3 102.proximal o I 0. 571 0 = => 3 104.blade- I ike I I . 000 0 = => I 106.neck below I 0. 500 0 I I I I . small late I 0. 625 I ---> 2 122.medial tar I 0. 333 0 ---> I 4 .stra ight q I 0. 500 0 ==> I 31.packed max I 0. 200 I ---> 0 45.curved pro I 0. 333 0 = => I 48.ant end of I 0. 333 0 I 98.short acet I 0. 500 I = => 2 105.upturned p I 0. 200 0 = => I 138 node_36 node_35 node_21 node_21 node_J35 node^34 node_22 node_22 node—34 —> node—35 —> node_21 —> Vandusaurus —> Otnielia —> node_34 —> node-22 —> Zephurosaurus —> Orodromeus —> node_33 66.surangular 13.vertica l q 63.narrow den 73.median rid 117. high ascen 123.ren iform I 45.curved pro 53.dentary ro 98.short cora 111. small late 3 I . packed max 118. high poste 3 .small QJ 12.squamosal 15. postorbita 23 .f la t front 51.dentary ti 70. basioccipi 72 .floor of b 81.5-6 sacraI 84.pubis cont 102.proximal o 109.la tera l Iy 7 . d is ta l Q s 10. groove on 20 .in fla ted p 38.pst apex o 44 .i uqal boss 49 .i uqal form 50 .i uqal touc 84.pubis cont 89.sharp scap 93. high olecr 94. cylindrica 116. D-shaped f 120.calcaneum 28.everted ma 37.max teeth 45.curved pro 75. BS longer 110. anterior i 119.low anteri 8 . Pterygoid 2I . socket for 23 .f la t front 3 I . packed max 68.no crest o 76. Nerve U en 112. proximal b 117. high ascen 6 . i uqal high 9 . Jugal wing 11. no p it on 16. quadratoju 62.post coron 71. small fora 77.opisto cer 80.16 or more 86.ossified h 95. ulna bowed 105.upturned p 111. small late 113. fibu lar co I 0.500 0 ---> I I 0. 500 0 --- > I I 0.333 I --- > 0 I 0. 500 0 ---> I 2 0.273 0 = => 2 I 0 .333 0 = => I I 0.333 0 = => I I 0.429 I = => 2 I 0.500 2 I I 0.625 2 I! 3 I 0.200 I — > 0 I 0,. 500 0 I I 0,.400 0 I I I 0,.333 0 — y I I 0,. 500 0 — > I I 0,.200 0 — > I I 0,,667 I ==> 2 I 0,.333 0 I I 0,.333 0 I I 0,.500 2 = = > 3 I 0..286 0 — > I I 0.,571 3 ==> 2 I 0.,333 0 == > I I I . ,000 0 ii I I 0 . 500 0 —> I I I . ,000 0 ii I I 0. 333 I —> 0 I 0.,500 0 ==> I I 0. 333 I 0 I 0. 500 I --- X 3 I 0. 286 I ==> 2 I I . 000 0 ==> I I 0. 333 0 —> I I 0. 500 0 —> I I I . 000 0 —> I I 0. 500 I ——> 0 I 0. 286 I = = > 0 2 0. 500 0 Il 2 I 0. 333 0 = = > I I 0. 400 I ii 2 I 0. 500 0 ii I 2 0. 250 0 = = > 2 I 0. 333 0 ii I I 0. 500 0 = = > I I 0. 200 I — > 0 I 0. 200 I — y 0 I 0. 333 0 I I 0. 500 0 I I 0. 429 2 —> I 2 0. 273 0 = = > 2 I 0. 400 I 2 I 0. 250 0 = = > I I 0. 500 0 — > I I 0. 333 0 — > I I 0. 500 I ==> 2 I 0. 500 2 —> I I 0. 333 0 —> I I 0. 600 I ——> 2 2 0. 500 0 ==> 2 I 0. 250 0 ii I I 0. 200 0 ——> I I <0 ■625 2 ii 3 I 0. 667 I ==> 2 139 node_33 —> ThesceIosaurus node^SS node_32 node_^ 32 node_31 node-38 ,node_30 —> node—32 —> Parksosaurus —> node—31 —> node—30 —> Hgpsilophodon —> node_29 27.5 or less 75.BS longer 110.anterior i 119.low anteri 12.squamosal 15. postorbita 28 .everted ma 33 .curved max 37 .max teeth 43.slender ju 48 .ant end of 5 0 .i uqal touc 74 .BO tubera 102.proximal o 103.large i l ia 123.re n iform I 16. quadratoju 31 .packed max 61 . dentary.ar 3 .small QJ 6 . Iuqal high 9 .Juqal wing 2 3 .f la t front 36 .continuous 53 . Dent teeth 58 . dentary ro 80.16 or more 105.upturned p 109.la te ra l Iy 112.proximal b 29 .recessed p 35 .maxiI Iary 39 .enamel on 54 . ridging on 55 . enamel one 5 6 . few dentic 59 . curved den 28 .everted ma 33 . curved max SS.dentary ro 8 7 .long cauda 91 .coracoid f 93 .high olecr 103.large i l ia 117.high ascen 5 .small pter 21 .socket for 27.5 or less 34 . no cingulu 53.Dent teeth 57 . no cingulu SS.dentary ro 6 0 .lozenge sh 62 . post coron 64 .predentary 71 . small fora 7 2 . floor of b 75 .ES longer 78 . dorsal spi 79 . r ib transi I 0.6671 I = => 0 I 0.400 I I = = > 2 I 0.500 0 = = > I 2 0.250 0 2 I 0.333 I ---> 0 I 0. 500 I ---> 0 I 0.286 I ---2 2 I 0. 500 0 I 2 0.500 0 ==> 2 I 0.500 I 0 I 0.333 0 ---> I I. 0. 500 I ==> 2 I 0.333 I ---> 0 I 0.571 2 ==> I I 0.250 0 ---> I I 0.333 0 ---> I I 0.333 I ---> 0 I 0.200 I ---> 0 I 0.333 I ==;> 0 I 0 . 400 I —> 0 I 0.400 2 —) 3 I 0.250 I —> 2 I 0.200 I —> 0 I 0.500 0 I I 0.333 0 —> I I 0.429 I —> 2 I 0. 600 2 —> I I 0.200 I —> 0 I 0.333 I —> 0 I 0.429 2 —> I I 0.500 I ==> 0 I 0 . 500 0 ==> I I 0. 500 0 ==> I I 0.500 0 ==> I I 0.500 0 ==> I I 0.500 0 ==> I 2 I . 000 0 ==> 2 2 0.286 2 ==> 0 I 0.500 I ==> 0 I 0.429 2 —> I I 0.333 0 ==> I I 0. 500 0 I I 0.333 0 ==> I I 0.250 I —> 0 I 0.273 0 I I 0.500 I —> 2 I 0. 500 0 —> I ■ I 0.667 I 2 I 0.667 0 I I 0.333 I ——> 0 I 0. 500 0 ——> I I 0.429 2 —> 3 I 0.500 0 —> I I 0.500 2 == > I I 0. 500 0 —> I I 0.500 I ==> 3 I 0.333 I —> 0 I 0.400 I —> 0 I 1.000 0 —> I I 0.667 I —> 2 140 node_33 node^33 node-^32 node^32 node_31 node—30 node—38 — > T h e s c e lo s a u ru s —> node-32 —> Parksosaurus — > node—31 —> nodeU30 —> Hupsilophodon —> node-29 27.5 or less 75.ES longer 110.anterior i 119.low anteri 12.squamosal 18.postorbita 28 . everted ma 33.curved max 37.max teeth 43.slender j u 48.ant end of 5 0 .i uqal touc 74. BO tubera 102.proximal o 103.large i l ia 123.re n iform I IS.quadratoju 31 .packed max 61 . dentary ar 3 .small QJ 6 . i uqal high 9 .Juqal wing 2 3 .f la t front 36.continuous 53 . Dent teeth 58. dentary ro 80.16 or more 105.upturned p 109.la te ra lly 112.proximal b 29 . recessed p 35.maxiI Iary 39 .enamel on 54 . ridging on 55 . enamel one 5 6 . few dentic 59. curved den 28 .everted ma 33 . curved max 58 .dentary ro 87 .long cauda 91 .coracoid f 93.high olecr 103.large i l ia 117.high ascen 5 .small pter 2 I . socket for 27.5 or less 34 . no cingulu 53 .Dent teeth 57 . no cingulu 58. dentary ro 60 .lozenge sh 62. post coron 64 .predentary 71 . small fora 7 2 . floor of b 75. ES longer 78 . dorsal spi 79 . r ib transi I 0.667 I = => 0 I 0.400 I 2 I 0.500 0 = => I 2 0.250 0 2 I 0.333 I ------- > 0 I 0.500 I -------> 0 I 0.286 I -------> 2 I 0. 500 0 = = > I 2 0. 500 0 = => 2 I 0.500 I = = > 0 I 0.333 0 ------- > I I 0. 500 I 2 I 0.333 I ------- > 0 I 0.571 2 = = > I I 0.250 0 ------- > I I 0.333 0 ------- > I I 0.333 I -------X 0 I 0.200 I ------- > 0 I 0.333 I = = > 0 I 0.400 I — > 0 I 0.400 2 ------- 2 3 I. 0.250 I ------- > 2 I 0.200 I ------- > 0 I 0. 500 0 I I 0.333 0 ------- > I I 0.429 I ------- > 2 I 0. 600 2 ------- > I I 0.200 I ------- > 0 I 0.333 I ------- > 0 I 0.429 2 ------- > I I 0.500 I 0 I 0.500 0 = = > I I 0.500 0 I I 0.500 0 = = > I I 0. 500 0 I I 0.500 0 = = > I 2 1.000 0 = = > 2 2 0.286 2 0 I 0.500 I = = X 0 I 0.429 2 -------X I I 0.333 0 I I 0.500 0 = = > I I 0.333 0 ==> I I 0.250 I ---> 0 I 0.273 0 ==> I I 0.500 I —> 2 I 0.500 0 ---> I I 0. 667 I ---X 2 I 0.667 0 ==> I I 0.333 I --- 0 I 0.500 0 ---> I I 0.429 2 —> 3 I 0.500 0 —> I I 0.500 2 ==> I I 0. 500 0 ---X I I 0.500 I 3 I 0.333 I ---S 0 I 0.400 I —> 0 I 1.000 0 ---> I I 0.667 I —> 2 141 node__29 node_28 node_28 node_27 —> node_28 —> Tenontosaurus —> node_27 —> node_26 8 2 .ta l l sacra 84 .pubis cont 9 6 .loss of ph 101. d is ta l foo 102. proximal o 112. proximal b 113 . fibu lar co 119.low anteri I 2I . round medi 124.3 function 6 .jugal high 9 .Jugal wing 13. vertica l q 19.robust pos 2 3 .f la t front 67 . surangular 98 .short acet 104.blade-1 ike 185.upturned p 110. an terior i 111. small late 6 . i uqal high l l .n o p it on 61 .dentarg ar 68 . no crest o 69 . supraoccip 121 . round medi 123.re n iform I 124.3 function 3 .small QJ 14 . jugal with 16.quadratoju 30 .premax con 84 .pubis cont 86 .ossified h 87 .long cauda 90 . short cora 93 .high olecr 9 7 .fused carp 100.bai—like s 102.proximal o 112.,proximal b 118.high poste 122. medial tar 2 .quadrate n 6 . jugal high 8 . Pterygoid 9 . Jugal wing 34.no cingulu 40 . PM sulcus 41 . high diamo 52 . pst apex o 53 . Dent teeth 91 . coracoid f 102.proximal o I I.. 000 I ==> 2 I 0.286 I ---> 0 2 0. 667 3 ---> 5 I 0. 500 0 ---> I I 0.571 I = => 3 I 0.429 I ---> 3 I 0.667 2 = => 3 2 0.250 0 2 I 0. 500 I ---> 2 I 0.500 0 ---> I I 0.400 3 ---> 2 2 0.250 2 ---> 0 I 0. 500 0 = => I I 1.000 0 ---> I I 0.200 0 ---> I I 1.000 I ---> 2 I 0.500 I = => 2 I 1.000 I = => 2 I 0.200 0 ---> I I 0.500 0 = => 2 I 0.625 3 ---> 4 I 0.400 2 = => I I 0. 500 I ---> 0 I 0.333 I 0 I 0.333 0 I I 0.500 0 = => I I 0. 500 2 ---> I I 0.333 I 0 I 0. 500 I ---> 0 I 0.400 0 — y I I 0.500 0 —> I I 0.333 I —> 0 I 0.333 0 —> I I 0.286 0 —> I 2 0.500 2 0 I 0.333 0 I I 0. 500 2 —> I I 0.333 0 ==> I I 1.000 0 —> I I I . 000 0 ==> I I 0.571 3 —> 0 I 0.429 3 4 I 0. 500 0 ==> I I 0.333 I 0 I 1.000 0 ==> I I 0.400 2 —> 3 I 0.333 0 I 2 0.250 0 —> 2 I 0.667 I 2 I 1.000 0 ==> I I 1.000 0 ==> I I 1.000 0 ==> I I 0.333 0 —> I I 0.500 0 ==> I I 0.571 0 — 'y 4 142 node_26 — > node_23 node_23 —> Dryosaurus node_23 —> Dysalotosaurus node_26 —> node_25 3 .small QJ 5 .small pter 2 3 .f la t front 42 .jugal not 46 . jugal u / a 49..jugal form 58 .dentary ro 76 .Merve U en 85 .caudal r ib 183.large i l i a 107.high lesse 112. proximal b 113 . fib u la r co I 17.high ascen 119.low anteri 121. round medi 9 . Jugal wing 30 .premax con 48 .ant end of 66 .surangular 84 .pubis cont 8 7 .long cauda 95 .ulna bowed 122. medial tar I . smaI l j uga 10. groove on 7 2 . floo r of b 75 .BS longer 3 .small QJ 15 .t a l l quadr 17.exoccipita 24 .small orbi 2 5 .long nasal 47 . round ecto 51 .dentary t i 58 .dentary ro 62 .post coron 70 .basioccipi 73 . median rid 80.16 or more 8 2 . t a l l sacra 83 . sacraI spi 90 .short cora 111.small late 115.Cylindrica I 0.400 I 2 I 0.500 2 ---> I I 0.200 I ---> 0 I 0.333 I ---> 0 I I .000 0 ==> I I 0.333 I ==> 0 I 0.429 3 = => 2 I 0,.500 0 ==> I I I,.000 I ==> 2 I 0,.250 I == > 0 I 0,.500 0 I I 0..429 4 ---> 2 I 0..667 3 ---> 2 3 0..273 0 ==> 3 2 0..250 2 ---> 0 I 0.,500 2 ---> I 2 0.,250 2 ---> 0 I 0. 333 I ---/ 0 I 0. 333 I ==> 0 I 0. 500 I I 0 I 0. 286 I ---2 0 I 0. 333 I ---> 0 I 0. 250 I ==> 0 I 0. 333 0 == > I I 0. 333 0 I I 0. 500 0 ==> I I 0. 333 0 ==> I I 0. 400 0 Il 2 I 0. 400 I —> 0 I 0. 500 I ---> 2 I I . 000 0 Ii I I I . 000 0 ==> I I I . 000 2 ==> 3 I I. 000 0 I I 0. 667 2 3 I 0. 429 3 ii 4 I 0. 500 I ==> 2 I 0. 333 I ==> 0 I 0. 500 0 ==> I I 0. 600 I ==> 2 I I. 000 2 ==> 3 I I . 000 0 ==> I I 0. 500 I —> 2 I 0. 625 4 —> 5 I I,. 000 0 ==> I 143 node_25 node_24 node_24 node_25 node_27 node_29 — > node_24 —> Iguanodon —> Ouranosaurus —> Camptosaurus —> Rhabdodon —> Gasparinisaura !.small juga 4 .s tra igh t q 14.jugal with 2 2 .fron ta ls s 26 .rearward f 46 .jugal w/ a 50 . jugal touc 63. narrow den 68 . no crest o 69 . supraoccip 75 .BS longer 79 .r ib transi 80.16 or more 90 .short cora 92 . hatchet-^h 93 . high olecr 94 . cylindrica 95 . ulna bowed 96 .loss of ph 114.Cnemial cr 51 . dentary t i 62 .post coron 111. small late 8 .Pterygoid 42 .jugal not 64 . predentary 71 .small fora 102.proximal o 105. upturned p 106. neck below 112. proximal b 12.squamosal 74 .BO tubera 77 .opisto cer 79 .r ib transi 84 .pubis cont 96 .loss of ph 28 .everted ma 39 .enamel on 51 .dentary t i 5 6 .few dentic 60 .lozenge sh 77 .opisto cer 84 .pubis cont 111.small la te !.small juga 15 .ta l l quadr 34.no cingulu 51 .dentary t i 70. basiocci.pi 81 .5 - 6 sacral 95 .ulna bowed 107. high lesse 109.la te ra l Iy 111.small la te 81 .5 - 6 sacral 117.high ascen I 0.333 0 I i I 0.500 0 i i I 0 . 500 I —— > 0 I I .000 0 ==> I I I .000 0 i I I I .000 0 = S S > 2 I 0. 500 2 ==> 3 I 0 .333 I I 0 I 0 .333 0 I I 0 .500 0 I I 0 . 400 0 ==> 2 I 0,.667 2 I 3 I 0,.600 2 3 I 0,. 500 2 ---> 3 I I..000 0 ==> I I 0..333 I ==> 2 I 0.. 500 0 I I 0.,250 I 0 I 0.,667 5 ---> 6 I I.,000 0 ==> I I 0.,667 3 ==> 4 I 0.,500 2 3 I 0.,625 5 ==> 6 I 0.,333 I ii 0 I 0. 333 I 0 I 0. 500 I 0 I 0. 500 3 I I 0. 571 4 ==> 3 I 0. 200 I 0 I 0. 500 I ==> 0 I 0. 429 4 ==> 3 I 0. 333 0 I I 0. 333 0 ==> I I 0. 333 I 0 I 0. 667 2 ==> I I 0. 286 I ---> 0 3 0. 667 5 2 2 0. 286 2 ==> 0 I 0. 500 I ==> 0 I 0. 667 2 I I 0. 500 I Tiii 8 I 0. 500 I ——> 0 I 0. 333 I — > 0 I 0. 286 I ==> 2 I 0. 625 4 — > 3 I 0. 333 0 ==> I I 0. 500 I ==> 2 I 0. 667 I 2 I 0. 667 2 ==> 3 I 0. 333 I 0 I 0. 500 3 2 I 0. 250 I ii 0 I 0. 500 0 == > I I 0. 333 0 — > I I 0. 625 3 ii 2 I 0. 500 2 == > 3 3 0. 273 0 ==> 3 node_ 3^8 --> Lesothosaurus 144 Apomorphy Explanations The following characters were run ordered, unless otherwise stated. : Cranial Characters ; 1. Quadrate with a small jugal wing. Primitively, the jugal wing is moderately sized. In “ Iguanodonts”, like Gasparinisaura, Dysalotosaurus, Iguanodon and Ouranosaurus, the jugal wing is shortened. Scored as: O=normal; 1=small jugal wing. 2. Quadrate notch present. Primitively in Lesothosaurus, a tiny foramen is formed between the jugal wing of the quadrate and quadratojugal (Sereno, 1991). A foramen i exists on the posterior side of the mid-portion of the quadrate in Heterodontosaurus, but it is unclear if this represents an homologous structure. Tenontosaurus exhibits a shallow fossa in the area of the mid-jugal wing, which may be incipient to the developed j. quadrate notch. The presence of the quadrate foramen, or notch, characterizes Dryosaurus and higher taxa, verifying analyses by Norman (1984; 1990), Milner & Norman (1984) and Coria & Salgado (1996). The quadrate foramen is eventually lost in the Hadrosauridae (Milner & Norman, 1984) Scored as: O= quadrate notch absent; J 1=present. 3. Small quadrate-quadratojugal articulation. Primitively, the quadratojugal articulates jf along half or more the length of the quadrate (over 3/4 in Heterodontosaurus). Thescelosaurus, Orodromeus, and Zephyrosaurus commonly share a quadratojugal contact of 1/3 the quadrate, with similar contacts seen in Parksosaurus and Rhabdodon. 145 Dryosaurus and Dysalotosaurus are united by small quadratojugals which lap less than 1/4 of the jugal wing of the quadrate. Scored as: 0= Contact 1/2 or more the length of quadrate; 1= contact between 1/2 and 1/4; 2= contact about 1/4 length of quadrate. 4. Proximal head of the quadrate not recurved posteriorly. Commonly among basal ornithopods, the quadrate head tilts strongly backward. In Agilisaurus this seems not the case. However, there is the possibility that the known Agilisaurus specimen is juvenile and not expressed in this individual. In Iguanodon and Ouranosaurus, the quadrate head is not recurved backward, even in adults. Scored as: 0=recurved; 1=straight. 5. Relatively small pterygoid wing on quadrate. In small ornithopods, the pterygoid wing of the quadrate forms a relatively large anteromedially extending fan of bone. In the larger ornithopods, like Tenontosaurus, Camptosaurus, lguanodon, and Ouranosaurus the pterygoid wing is much reduced. Scored as: O=Iarge to normal; 1=small. 6. Jugal or quadratojugal meets the quadrate well above the quadrate foot. Uniquely in Lesothosaurus, the quadratojugal meets the quadrate at the distal end. In Heterodontosaurus, Yandusaurus, Zephyrosaurus, Orodromeus, and Tenontosaurus the quadratojugal or jugal meets near the distal end of the quadrate. Thescelosaurus, Parksosaurus, and Rhabdodon have quadratojugals that join the quadrate, at its lowest point, above the distal condyles. Hypsilophodon, Gasparinisaura, and higher ornithopods inclusive of Dryosaurus possess a jugal\quadratojugal bar that meets the well above its distal end. Sereno (1986) used the quadratojugal meeting the jugal high above the jaw articulation to unite the Dryomorpha. If the emphasis is on the 146 quadratojugal, this coincides with the reduced quadratojugal found in Dryosaurus, Dysalotosaurus and Camptosaurus (See character 3). If the emphasis is on the articulation as being well above the distal end of the quadrate, then Hypsilophodon and Gasparinisaura would be included with Dryosaurus and higher. Scored as: 1=near distal end; 2= above; and 3= well above. 7. Distal end of quadrate slopes dorsolaterally. When the quadrate is oriented upright in Lesothosaurus, both the lateral and medial condyles of the distal end of the quadrate lie on a horizontal plane. Similarly, Dryosaurus, Tenontosaurus, Camptosaurus, and Iguanodon share this state. Common in other taxa, the distal condyles of the quadrate slope slightly dorsomedially. In contrast, Zephyrosaurus and Orodromeus possess a quadrate with a distal end sloping dorsolaterally. Scored as: Odorsomedial - horizontal; 1= dorsolateral. 8. Pterygoid wing emerges from below the dorsal head of the quadrate. Among the taxa scored for this feature, Orodromeus, Dryosaurus, Dysalotosaurus, Camptosaurus and Iguanodon share the derived state where the pterygoid wing emerging below the proximal end of the quadrate. Common among the rest of the taxa scored is a pterygoid wing emerges from the head of the quadrate. Scored as: O= at; 1= below dorsal head. 9. The ventral extent of the jugal wing ends well above the distal condyles of the quadrate. In Lesothosaurus;Heterodontosaurus, Yandusaurus, Zephyrosaurus, Orodromeus, Dryosaurus, Tenontosaurus and Rhabdodon the jugal wing returns ventrally to the main body of the quadrate at, or near, the distal end. The quadrates in Thescelosaurus and Parksosaurus are slightly more derived in ending a little higher. 147 The remaining taxa scored (Hypsilophodon, Gasparinisaura, Dysalotosaurusi Camptosaurus, lguanodon, and Ouranosaurus) all have jugal wings which return high above the distal end of the quadrate. Scored as: 0= at or near distal end; 1= above; 2= well above. 10. Presence of a groove on the base of the posterior side of the pterygoid wing of the quadrate. Commonly among the more primitive-grade ornithopods, there is no groove present on the pterygoid wing of the quadrate. Zephyrosaurus is unique in this feature, with Orodromeus possessing a distinct fossa in the same region. Although this fossa in Orodromeus is not as developed as in Zephyrosaurusi cladistic analysis indicates the feature is likely an homologous character. Scored as: 0= absence; 1= groove or fossa present. 11. Absence of lateral pit in mid-quadrate shaft. Primitively, a pit occurs along the lateral side of the quadrate at the base of the jugal wing. Although faint, a pit occurs in Lesothosaurus, Heterodontosaurus, Orodromeusi and Zephyrosaurus. In Zephyrosaurusi this feature is developed into more of an abbreviated groove. All other taxa scored lacks this feature, although in Tenontosaurusi a faint depression occurs in this region. Scored as: 0= pit present; 1= no pit. 12. Long ventral process on squamosal. Primitively, the ventral process of the squamosal laps anteriorly down 20-30% the length of the quadrate. The derived state occurs within the Zephyrosaurus-Orodromeus clade and Thescelosaurus where the squamosal extends down more than 30% of the quadrate. Equally derived, although not uniting taxa, are those with shortened squamosals which lap less than 20% the anterior 148 edge of the quadrate. These taxa include Hypsilophodon, Parksosaurus, Dysalotosaurus and Ouranosaurus. Scored as: 0= < 30% length of quadrate; 1=>30%. 13. Quadrate oriented vertically. Most taxa exhibit a somewhat posteriorly leaning quadrate. Yandusaurus, Tenontosaurus, Dryosaurus, Dysalotosaurus, Camptosaurus, lguanodon, and Ouranosaurus possess essentially vertically oriented quadrates This character is interpreted as being autapomorphic for Yandusaurus, and phylogentically significant for the higher “iguanodontian-grade” ornithopods. Scored as: 0= posteriorly leaning quadrate; 1= vertical. 14. Jugal articulates with quadrate. The common state within most basal ornithopods, is a q u ad ratoj u g a l-q u ad rate articulation. In Dryosaurus, Dysalotosaurus, and Camptosaurus, the quadratojugal is much reduced and bordered ventrally by the jugal, allowing a jugal-quadrate contact. Scored as: 0= jugal fails to contact quadrate; 1= jugal articulates with quadrate. 15. Tall and narrow quadratojugal. The size of the quadratojugal appears very large in the derived state seen in Heterodontosaurus. The other extreme is exhibited in the reduced quadratojugal found in Dryosaurus, Dysalotosaurus and Camptosaurus. In lguanodon, Ouranosaurus and Gasparinisaura, the quadratojugal is very reduced anteroposteriorly, but tall. Reduction of the quadratojugal defines Serene’s Iguanodontia (Sereno, 1986) or Dryosauridae and higher taxa (Norman, 1990; Coria & Salgado, 1996; Salgado & Others, 1997.) Weishampel & Heinrich (1992) used a reduced quadratojugal to unite Yandusaurus and Othnielia, as well as being diagnostic for Dryosaurus and 149 higher taxa. Scored as: 0= quadratojugal normal to short; 1= tall and narrow. 16. Quadratojugal foramen present. In most ornithopods, no foramen occurs within the quadratojugal. However, a foramen is present in the quadratojugal for Thescelosaurus, Hypsilophodon, Tenontosaurus, and Gasparinisaura,. This feature may be the precursor for a more posteriorly migrated quadratic notch. Foramen fully within the body of the quadratojugal (Norman, 1990) Scored as: 0= foramen absent; 1= present. 17. Exoccipital not part of the occipital condyle. Although unable to differentiate the exoccipital from the opisthotic in any of the taxa under consideration here, the posteroventral corner of which would normally constitute the exoccipital, participates, primitively within the group, as the dorsolateral corners of the occipital condyle. Only in Camptosaurus, Iguanodon and Ouranosaurus is the occipital condyle only comprised of the basioccipital. Scored as: 0= exoccipital contributes to part of occipital condyle; 1 = occipital condyle entirely composed of basioccipital. 18. Postorbital with rugose orbital edge. Common among most scored taxa, the orbital edge of the postorbital forms a sharp, clean edge. In Zephyrosaurus, Orodromeus, and Thescelosaurus this edge is striated and rugose probably for attachment of the eyelid or for the posterior extension of the supraorbital. Scored as: 0= clean edged postorbital; 1 = striated and rugose orbital edge. 19. Robust postorbital. Among those taxa with postorbitals available, Lesothosaurus and Gasparinisaura possess relatively lightly constructed postorbitals. Camptosaurus, Iguanodon and Ouranosaurus exhibit robust postorbitals, while postorbitals in the remainder of taxa have an intermediate build. Scored as: 0= non-robust; 1= robust 150 postorbitals. 20. Postorbital with an anteriorly inflated orbital edge. Primitively among the analyzed taxa, Heterodontosaurus and Scutellosaurus, as well as in many higher taxa, the orbital profile of the postorbital forms a continuous arc (scored 0). Other taxa including Lesothosaurus, Yandusaurus, Othnielia, and Dryosaurus have postorbitals with subtle inflation (scored 1). More developed in Orodromeus and Zephyrosaurus, a distinctive anteriorly directed inflation occurs along the upper half of the orbital edge. Scored as: 0=non developed postorbital; 1= inflated postorbital. 21. Socket for the head of the Iaterosphenoid occurs only within the postorbital. Although there is a lot of missing data, the available comparisons suggest the primitive state within the Ornithopoda is the positioning of the synovial socket receiving the coty I us of the Iaterosphenoid is shared ventrally by both the frontal and postorbital. In other taxa (Orodromeus, Tenontosaurus, Dryosaurus, Camptosaurus and Ouranosaurus) the synovial socket lies primarily, if not exclusively, within the under side of the postorbital. Iguanodon appears to lack this feature. This character is considered as uniting the “iguanodontid grade” taxa, with it independently aquired in Orodromeus. Scored as: 0= socket in frontal and postorbital; 1= socket only in postorbital; 2= no synovial joint. 22. Frontal length less than 3/4 combined width. Sereno (1986) and Weishampel & Heinrich (1992) defined the Hypsilophodontidae above Thescelosaurus in part on the relatively narrow frontals. Typically throughout small ornithopods, frontals measure longer than their combined width. This varies ontogenetically within Dryosaurus, 151 Orodromeus, and in the Proctor Lake ornithopod. Younger animals, due to the considerably larger orbits relative to skull size, have narrow frontals. Lesothosaurus, Yandusaurus, Thescelosaurus, Tenontosaurus and Camptosaurus have frontals nearly as long as their combined widths. Iguanodon and Ouranosaurus have unusually short frontals, nearly twice as wide as they are long. Scored as: 0= combined width of frontals <1.5 their length; 1= >1.5; 23. Flat frontals. Primitively, bipedal herbivorous dinosaurs possess frontals that arch somewhat over the orbits! Zephyrosaurus, Thescelosaurus, Parksosaurus and Tenontosaurus have flat frontals, as do the larger taxa lguanodon, Ouranosaurus and Camptosaurus. Scored as: 0= arched frontals; 1= dorsally flattened frontals. 24. Small percentage of frontal forms orbital edge. More commonly among the analyzed taxa, well over 1/4 of the length of the frontals border the orbit. More extreme in Parksosaurus and Gasparinisaura, the orbital edge of the frontals measures nearly 1/2 its length. Camptosaurusv lguanodon and Ouranosaurus have short frontals, but are nearly excluded from bordering the orbit. Taxa scored as: 0= orbital edge well over 25% frontal length; 1= <25% frontal length. 25. Ratio of frontal length to nasal length less than 60%. In Lesothosaurus, frontals measure over 120% that of the short nasals. In Heterodontosaurus and within most of the scored taxa, frontal length compares more equally to the nasals and somewhat shorter. Camptosaurus, lguanodon and Ouranosaurus possess relatively long nasals and abbreviated frontals, less than 60% nasal length. Taxa were scored 1= >120%; 2= 152 60-120%; 3= <6%. 26. Rearward migration of the frontals. Commonly in small ornithopods, the dorsal frontal-parietal suture is spaced moderately behind the orbit. Iguanodon and Ouranosaurus are unusual in having had a backward migration of the frontals with the anterior edge of the frontals above and anterior to mid-orbit. The frontal-parietal suture resulted as more than 25% orbital length, posterior to the orbit. Scored as: 0= frontals over orbit. 1= frontals posterior and over posterior half of orbit. 27. Five, or less premaxillary teeth. Primitively, within the Ornithischia, each premaxilla contains six teeth. This is observed in Scutellosaurus, Lesothosaurus, Heterodontosaurus, and interestingly in Thescelosaurus. Other than the anomalous Thescelosaurus, all other ornithopods analyzed exhibited five or less teeth in each premaxilla. Most of the iguanodontid-grade ornithopods, Dryosaurus and higher, have been partly defined by the absence of premaxillary teeth (Norman, 1984; Milner & Norman, 1984; Coria & Salgado 1996; Salgado & Others 1997; Weishampel & Heinrich, 1992 [lguanodontia]; Sereno, 1986 [lguanodontia]). Scored as: 0= 6 premaxillary teeth; 1= 5 teeth; 2= no teeth in premaxilla. 28. Everted and broad oral margin of the premaxilla. Variation of the general shape of the premaxillary beak occurs among taxa. Some taxa exhibit a rather pointed, steep sided rostrum (i.e. Scutellosaurus, Heterodontosaurus, Lesothosaurus, Zephyrosaurus, Hypsilophodon and Rhabdodon). A few taxa, like Orodromeus, Agilisaurus and Thescelosaurus, possess premaxillae which are slightly everted along the bottom edges. 153 Bugenosaura and the iguanodontian-grade ornithopods all have an upper rostrum distinctively flared along the lower edges, precursors to the much more derived flattened premaxillae of the “duck-billed” dinosaurs. This character was diagnosed as a synapomorhpy for Iguanodontia (Sereno, 1986; Weishampel & Heinrich, 1992; Coria & Saigado 1996; Salgado & Others 1997.) Scored as: O= non-flared premaxilla; 1 =SlightIy flared or everted oral margin of the premax; 2= everted oral margin of the premaxilla. 29. Premaxillae with a posterolateral recess for receipt of the maxillary boss. The premaxillae of Zephyrosaurus, Orodromeus, Thescelosaurus and Bugenosaura all possess a concavity within the posterior end, near the lateral margin, that nestles the anterolateral boss of the maxilla. Although this character suffers from missing data, it is reasonable to assume that most of the small basal ornithopods above Lesothosaurus possessed this character. No posterior recess exists in Hypsilophodon and higher taxa and a maxillary boss is not developed, with the exception of Rhabdodon, which, possesses a maxillary boss but is not complimented by the premaxilla. Scored as: O= absent; 1= present. 30. Premaxilla contacts lacrimal. Primitively in Lesothosaurus and among ornithiscians the posterior ascending process extends between the nasals and the maxilla, but does not reach the lacrimal (Gauthier, 1986; Sereno, 1986). This condition is common among small ornithopods (Weishampel & Heinrich, 1992) and used as a character to unite the Hypsilophodontidae and Tenontosaurus. In Heterodontosaurus, Dysalotosaurus, Camptosaurus, Iguanodon and Ouranosasurus however, the premaxilla extends beyond and over the maxilla to contact the lacrimal. Scored as: 0=no lacrimal contact; 1 = 154 lacrimal contact. 31. Packed maxillary teeth. Although somewhat subjective, there exists a difference in the relative closeness of maxillary teeth. Agilisaurus and Orodromeus both possess somewhat pointed maxillary teeth, which only comes close to contact with a neighboring tooth near its base. Scutellosaurus, Lesothosaurus, Othnielia and Parksosaurus all have teeth that are slightly wider which nearly contacts its neighbor near mid-length. Packed teeth found in the remaining taxa are defined on the lack of space between teeth up through the occlusal margin, defined by Norman (1984) and Milner & Norman (1984) as adjacent interlocking teeth uniting Hypsilophodontidae with higher taxa. A further transitional stage is found in Sereno’s Ankylopollexia by the close packing of teeth along the tooth row and in the replacement series eliminating spaces between the bases of the crowns of adjacent functional teeth (Sereno, 1986.) Scored as: O= non- packed teeth; 1= packed. 32. Maxillary and dentary teeth inset. Dentary and maxillary teeth set medial to the edge of the lateral mandibular and maxillary margins was considered by Galton (1972, 1973) to be indicative of the presence of cheeks. Only Scutellosaurus and Lesothosaurus illustrate tooth rows along the outer margins of the maxilla and dentary. Agilisaurus and Othnielia have maxillary teeth only modestly inset within the cheeks. All other taxa above the “fabrosaurid condition” throughout ornithischia exhibit teeth moderately well inset, except for the extreme condition found in Bugenosaura in which the cheek teeth are set far within an awning created by the maxilla. Scored as: O= teeth not inset; 1= cheek teeth at least modestly inset. 155 33. Curved maxillary tooth roots. Primitively among the ornithischia, maxillary tooth roots are straight. Within the ornithopods, there is a tendency among the higher taxa for curved tooth roots, being more extreme in Dryosaurus. Scored as: 0= straight tooth roots; 1= curved tooth roots. 34. No cingulum on maxillary tooth crowns. Primitively, in Scutellosaurus and Lesothosaurus, maxillary tooth crowns possess a moderate swelling at the base of the tooth crown. In Zephyrosaurus and Hypsilophodon, this cingulum is modest, but nearly absent in Tenontosaurus and Rhabdodon. In Gasparinisaura, Dryosaurus, Camptosaurus and lguanodon, the enameled crown tapers gradually to the root, lacking a cingulum. Scored as: 0= cingulum present; 1= no cingulum. 35. Maxillary crown gradually tapers to root. This appears at first to be correlated to the lack of a cingulum, and although there is a relationship between this and character 60, the scoring of this character reveals these characters are not wholly dependent on the other, and should be considered separately. Heterodontosaurus, Dryosaurus and Camptosaurus have crowns that neck-down very modestly, unlike the constricted necks found in small ornithopods that clade' below Hypsilophodon. Although Hypsilophodon maxillary teeth have a slight cingulum, there is no modest constriction of the root below the crown. Maxillary crowns in Gasparinisaura, Tenontosaurus and lguanodon likewise taper to their roots. Scored as: 0= distinct neck below crown; 1= crown tapers to root. 36. Maxillary teeth form a continuous occlusal surface. Ornithopod taxa above Bugenosaura and Hypsilophodon exhibit a continuous, shared masticating surface 156 across the maxillary teeth. This suggests cheek teeth were functioning as one unit against the mandibular set with improved alignment and uniform directional forces. Heterodontosaurus possesses a similar outcome in a different fashion (see Norman, 1984; 1991). Scored as: 0= teeth independently occlude. 1= teeth share a continuous : occlusal surface. 37. Maxillary teeth Iingually convex. Primitively in Lesothosaurus, Scutellosaurus, j: Yandusaurus, Orodromeus and Thescelosaurus, maxillary teeth are not convex lingually. In Zephyrosaurus, Parksosaurus and taxa above, the occlusion of maxillary teeth are well supported by a convex lingual side. Scored as: 0= concave; 1=convex. 'r 38. Maxillary teeth with posteriorly-set apical ridge.. Orodromeus retains the primitive ;! state with Scutellosaurus, Heeterodontosaurus and Agilisaurus in having a centrally | placed apex. All other taxa show the apical ridge to be slight- to well-posterior of center. ) I' Scored as: 0= Central apical ridge; 1= posterior. i I 39. Maxillary teeth with enamel restricted to one side. All taxa higher than, and including Hypsilophodon, with the exception of Rhabdodon, exhibit upper cheek teeth with noticeably thicker enamel on the labial side. In the higher iguanodontian-grade ornithopods, there still exists a thin veneer of enamel on the labial side (contra Sereno, 1986; Coria & Salgado 1996; and Salgado & Others 1997 for Dryomorpha and higher taxa), but here it is very thin and illustrates a stage before the hadrosaurid condition with an eventual lack of enamel on the inner side. Scored as: 0= equally enameled maxillary teeth; 1= enamel primarily on lingual side. 40. Premaxillary sulcus on the anterior process of the maxilla. In Lesothosaurus and 157 basal ornithopods, the anterior end of the maxilla bears a spike-like process which inserts into a deep recess above the palate in the posterior end of the premaxilla. Norman (1984) and Milner & Norman (1984) identified maxillae meeting at midline (anterodorsally) in recess of premaxilla, as a defining character for Hypsilophodontidae.and higher taxa. However, In Dryosaurus and higher taxa, the anterior end of the maxilla is flattened horizontally and bears an anterodorsal sulcus to receive the posterior portion of the premaxilla. The presence of this sulcus, in essence, creates two maxillary processes which defines Dryomorpha with higher taxa (Weishampel & Heinrich, 1992; Coria & Salgado 1996; Salgado & Others 1997), or diagnosed by Sereno (1986) for lguanodontia. In contrast to the primitive condition, the anterior end of the maxilla does not enter into the posterior end of the premaxilla, but ventral to it. Scored as: O= spike-like process of maxilla; 1= sulcus. 41. High diamond-shaped maxillary tooth crowns. A variety of tooth shape occurs among small ornithopod dinosaurs, but very little grouping results when each shape is scored separately. The only tooth shape that correlates with characters which support the proposed phytogeny is found in Dryosaurus and higher taxa. These teeth were described by Sereno (1986) as diamond-shaped maxillary crowns with rounded anterior and posterior corners uniting Dryomorpha. Alternatively, they are described simply as high maxillary tooth crowns by Weishampel & Heinrich (1992); Coria & Salgado 1996; Salgado & Others 1997 for Dryosaurus and higher taxa. Broad asymmetrical teeth are described by Milner & Norman (1984) as unique for Iguanodontidae only, and 158 lanceolate-shaped maxillary crowns defined Serene’s (1986) Styracosterna. Scored as: 0= maxillary crowns relatively low spade-like, rectangular, or triangular; 1= high diamond-shaped maxillary crowns. 42. Jugal excluded from bordering antorbital fenestra. Primitively in Lesothosaurus and Heterodontosaurus, the antorbital fenestra is bounded by the maxilla, lacrimal, and briefly by the anterior process of the jugal This primitive condition re-appears in Dryosaurus and Ouranosaurus. All other taxa analyzed possess an antorbital fenestra only bounded anteriorly and ventrally by the maxilla, and posteriorly and dorsally by the lacrimal. With the available material, this character was described by Weishampel & Heinrich (1992) as uniting Parksosaurus and Hypsilophodon, independently acquired in . Tenontosaurus. Coria & Salgado (1996) and Salgado & Others (1997) use this character to diagnose Euornithopoda. Scored as: O= antorbital fenestra bounded by maxilla, lacrimal and jugal.; 1= only maxilla and lacrimal; Jugal excluded from bordering antorbital fossa. 43. Slender jugal. The ratio of the greatest posterior expanse of the jugal over the height of the skull was measured in all taxa with available material. Yandusaurus, Orodromeus, Zephyrosaurus and Thescelosaurus bear jugals less than 1/4 skull height. All other taxa have jugals nearly 1/3 or greater the height of the skull, Heterodontosaurus and Tenontosaurus being more extreme in measuring nearly half the skull height. Scored as: 0= jugals >1/4 skull height; 1= jugals <1/4 skull height. 44. Jugal horn or boss present. Among ornithopods only in Orodromeus and 159 Zephyrosaurus does the jugal present a prominent lateral horn (Weishampel & Heinrich, 1992). A jugal boss is present in Heterodontosasurus, the sister taxon to ornithopods, and is common among armored and horned ornithischian dinosaurs, but is considered here to be an apomorphic character in ornithopods. The absence of a jugal boss has been considered the derived state for Euornithopoda (Weishampel & Heinrich, 1992; Coria & Salgado 1996; Salgado & Others 1997). Scored as: O= jugal boss absent; 1 = present. 45. Dorsally curved anterior process of jugal. In Agilisaurus, Yandusaurus and Zephyrosaurus the anterior process of the jugal curves upward. In all other taxa scored, the anterior process ends abruptly as it meets the maxilla and lacrimal. Scored as: O= Straight; 1= curved. 46. Anteromedially arched maxillary process on the medial side of jugal. Although this character if fraught with missing data, the available comparative material suggests in basal ornithopods the maxillary process of the jugal extends medially and is only modestly arched. Dryosaurus and Dysalotosaurus are united in possessing a straight groove for the insertion of posterior flange on the maxilla. In Iguanodon and Ouranosaurus, the maxillary process on the jugal is noticeably anteromedially projected and arched. Scored as: O= medially projected and modestly arched; 1= straight grooved; 2= anteromedial and arched. 47. Ectopterygoid articular facet on medial jugal round in shape. As with the previous character, the scoring of this feature suffers from missing data. The available material suggests basal ornithopod dinosaurs have an abbreviated deep groove for the insertion 1 60 of the ectopterygoid, whereas in Camptosaurus, Iguanodon and Ouranosaurus the articulation point appears as a rounded scar. Scored as: deep=0; rounded=1 48. Anterior end of jugal contacts the maxilla. In Lesothosaurus, Heterodontosaurus, Orodromeus, Zephyrosaurus and Thescelosaurus, the anterior process of the jugal appears, in lateral view, to lap over the posterior maxilla with the jugal ending above the maxilla. In lateral view of skulls of Bugenosaura and higher taxa, the anterior end of the jugal ends into the maxilla. Agilisaurus and Dryosaurus appear as unusual in their phylogenetic context in respect to this articulation. The Agilisaurus jugal ends into the maxilla, and in Dryosaurus the maxilla ends above the maxilla. Scored as: O= jugal ends above maxilla; 1= anterior end of jugal ends within maxilla. 49. Jugal forms an oblique angle bordering the infratemporal fenestra. In Lesothosaurus and Heterodontosaurus and in the Orodromeus-Zephyrosaurus and Dryosaurus-Dysalotosaurus clades, the anteroventral corner of the infratemporal fenestra is a narrowly acute angle formed by the jugal. In the remaining ornithopods, the jugal forms an oblique to right angle here. Scored as: O= oblique to right angle; 1= jugal forms acute angle. 50. Jugal barely touches lacrimal. In the outgroup taxa and commonly within small ornithopods, the anterior end of the jugal meets the posteroventral edge of the lacrimal. In lguanodon, Ouranosaurus and Orodromeus this contact is a firm butt joint. In Yandusaurusl Agilisaurus and Thescelosaurus, the anterior end of the jugal barely touched the lacrimal. Run unordered and scored as: 1 = jugal just touches lacrimal; 2= 161 jugal meets lacrimal with more contact; 3= lacrimal-jugal butt joint. 51. Low anterior dentary tip. There occurs a general trend through the evolution of the orntihopods where the anterior tip of the dentary articulates progressively lower into the predentary. The outgroup taxa Scutellosaurus, LesothosaUrus and Heterodontosaurus, have dentary tips which extend rostra I ly, high at the anterior end. Yandusaurus and Agilisaurus (and the enigmatic Rhabdodon) retain dentary tips which are pointed at mid­ tip. The higher grade of ornithopods from Orodromeus through Dryosaurus have a dentary tip slightly lower. Gasparinisaura, Camptosaurus and Ouranosaurus possess a lower tip, and lguanodon, very low. Scored as: 1 =Ngh1 2=mid, S=-Iow1 4=low, S=IowI 52. Posterior apical ridge in dentary teeth. In small ornithopod taxa and in their sister taxa, the primary apical ridge of mandibular teeth is situated within the center, or slightly anterior of center, of the tooth crown. In Dryosaurus and higher taxa, the apex of the tooth is posterior to center of the tooth crown. Scored as: O= anterior to centered; 1 = posterior. 53. Mandibular crowns possessing primary, secondary and tertiary ridges. Primitively in Lesothosaurus and Heterodontosaurus, as well as throughout most small ornithopods, the dentary tooth crowns possess equally prominent ridges, and in some cases, secondary ridges. In Bugenosaura, Hypsilophodon, Dryosaurus and higher taxa, the dentary tooth crowns bear primary, secondary, and tertiary ridges. This character was used in part by Norman (1984; 1990) to diagnose Camptosauridae and higher taxa. Scored as: 0= primary and some secondary ridges; 1= crowns with primary, secondary and tertiary ridges. 162 54. Mandibular teeth possess ridges on only one side. In Scutellosaurus, short ridges occur on either side of the dentary crowns. This condition is found in the basal ornithopods Othnielia, Zephyrosaurus, Thescelosaurus, Parksosaurus and Bugenosaura and is interpreted here as the primitive condition. However, in the primitive Heterodontosaurus, ridges on tooth crowns are limited to one side. This condition reappears in Hypsilophodon and higher taxa and is interpreted as the derived condition in ornithopods. Scored as: 0= ridges on both sides of crown; 1=ridges limited to one side. 55. Mandibular teeth with thickened enamel on only one side Enamel restricted to distal half of crown on the medial side of the maxillary teeth and the lateral side of the dentary teeth was a character used by Sereno (1986) for lguanodontia. Analysis of taxa for this character verifies Norman’s (1990) conclusion: there is a tendency through the evolution of the ornithopods for the enamel to thin dramatically on the lateral side of mandibular teeth and medial side of maxillary teeth. Although occurring as a thin veneer in the iguanodontid grade ornithopods, enamel doesn’t disappear on these edges until in hadrosaurs. However, none of the taxa observed in this study possess enamel restricted to the distal half of the crown. Interestingly, enamel thinning on one side is observed in Heterodontosaurus, then latter in all taxa above and including Hypsilophodon. Scored as: 0= both sides enameled; 1= primarily one side enameled. 56. Only some denticles on mandibular crowns supported by ridges. Through most small ornithopod taxa, dentary crowns possess denticles supported by ridges. Except in 163 Rhabdodon, Hypsilophodon and higher taxa bear many denticles unsupported by ridges. Previous workers (Weishampel & Heinrich, 1992 (described this character, but inadvertently listed absence as derived state); Coria & Salgado 1996; Salgado & Others 1997) describe ridges confluent with marginal denticles of cheek teeth as derived for Hypsilophodontidae. However, this definition encountered problems because many of the hypsilophodontian-grade ornithopods have very short or absent ridges. In higher ornithopods, such as Dryosaurus and above, most ridges do not extend to outer margin. Scored as: O= all with ridges; 1= Some denticles with ridges. 57. No cingulum on dentary teeth. A modest cingulum is present at the base of the crown in several small ornithopods and described as unifying the Hypsilophodontidae (Weishampel & Heinrich, 1992). A cingulum is common throughout most of the ornithischia, being very pronounced in nodosaurs, ankylosaurs and pachycephalosaurs. Among basal ornithopods, Zephyrosaurus and Thescelosaurus possess a very modest cingulum, but the cingulum is lost in Tenontosaurus and higher taxa. Heterodontosaurus is interpreted as having lost the cingulum independently. Scored as: O= modest cingulum; 1= cingulum lost. 58. Dentary tooth roots squared in cross-section. The shape of the tooth roots only shows a rough trend through the evolution of ornithopods. In Scutellosaurus and Lesothosaurus, tooth roots are circular in cross-section. This same condition is retained throughout much of the cladogram, although Heterodontosaurus, Yandusaurus, Bugenosaura1 Dryosaurus and Dysalotosaurus have roots with an oval-shaped cross- section. The dentary tooth roots of Tenontosaurus and Rhabdodon are found squared 164 as are those of Camptosaurus, Iguanodon and Ouranosaurus, but in this latter set of taxa each root bears a longitudinal groove caused by the interlocking adjacent tooth. Scored as: dentary tooth roots round in cross-section; 2= oval; 3= squared; 4= squared and grooved. 59. Curved dentary roots. Primitively, dentary tooth roots are straight and tapered. As observed by Bakker and others (1990), Hypsilophodon and higher taxa possess tooth roots which curve . Scored as: 0= straight roots; 1= curved. 60. Lozenge-shaped dentary crowns. There exists much variety in tooth shape among small ornithopod dinosaurs. Unfortunately, very little grouping results when each shape is scored separately. The only tooth shape that correlates with characters which support the proposed phytogeny is found in Tenontosaurus and higher taxa. These tall crowns are roughly oblong-oval, or lozenge-shaped. Caution must be exercised however, for hatchling and young juveniles of many of these higher taxa still retain a more leaf­ shaped tooth crown. Scored as: 0= dentary crowns rectangular, triangular, or leaf­ shaped; 1= crowns lozenge-shaped. 61. Dentary arched inward. In sister taxa to the ornithopods, the dentaries are straight. Yandusaurus, Othnielia and higher taxa possess dentaries which bow medial. Parksosaurus and Tenontosaurus re-acquired a straighter lower jaw. Scored as: 0= straight dentaries; 1= dentaries arched inward. 62. Post-coronoid elements of lower jaw relatively short. The posterior jaw complex consisting of the surangular, angular, prearticular and articular comprises 35-40% the length of the tower jaw in small primitive and ornithopod taxa. A posterior complex 165 measuring 25-35% is found in Thescelosaurus, Parksosaurus, Hypsilophodon and Cannptosaurus. This portion posterior to the coronoid process of the dentary is further abbreviated in Iguahodon and higher taxa where this region measures less than 25% the length of the lower jaw. Scored as: 1= 35-40% of lower jaw; 2= 25-35%; 3= less than 25%. 63. High ratio of dentary depth/length. Weishampel & Heinrich (1992) proposed parallel dorsal and ventral margins of the dentary as a character to unite the lguanodontia, and was subsequently repeated by Coria & Salgado (1996) and SaIgadO & Others (1997). When quantified, this character appears somewhat homoplastic. Parallel dentary margins constitute an adult trait in several taxa, so without comparable ontogenetic material, ,the character could be problematic. To quantify this character, taxa were scored based on the height of the dentary, just anterior to the rising coronoid process, divided by the length of the element. Scutellosaurus and Lesothosaurus represent the primitive condition with the dentaries fairly slender. Othnielia and Yandusaurus pair off, as well as Iguanodon and Ouranosaurus, as having relatively slender dentaries for their length. Scored as: 0=15-20%; 1=20-35%. 64. Predentary with two posteroventral processes. Described as “anterior process of the predentary paired” by Coria & Salgado (1996) and Salgado & Others (1997) for Dryomorpha, it is assumed the description of ‘anterior process’ is a misprint and should be corrected to the Ventral process paired or bifurcate’ as described by Sereno (1986) and Weishampel & Heinrich (1992) for lguanodontia, and Norman (1984) and Milner & Norman (1984) for Dryosauridae and higher taxa. Ijhis analysis identifies this character 166 as apomorphic for taxa higher than and inclusive of Tenontosaurus. Scored as: 0= predentary with single posteroventral process; 1= posteroventral process paired or bifurcate. 65. No external mandibular fenestra. In Lesothosaurus, Scutellosaurus and Heterodontosaurus, the lower jaw bears a mandibular fenestra located at the junction of the dentary, surangular and angular. In all ornithopods this character is lost (Ser.eno, 1986). Scored as: 0= mandibular fenestra present; 1= absent. 66. Surangular foramen present. In Orodromeus and higher taxa, the posterior jaw bears a lateral foramen high within body of the surangular. This occurs in addition to the common small foramen located within the surangular tuberosity just anterior to the jaw articulation. The high lateral foramen of the surangular may be homologous to the lateral mandibular fenestra found in the sister taxa, but this cannot be determined with available material. Scored as: O= no surangular foramen; 1= surangular foramen present. 67. Dorsal margin of the surangular concave in lateral view. The primitive condition seen in Lesothosaurus, is a convex surangular margin. Although a nice transformation series of gradual change does not occur sequentially across the cladogram, the general trend through ornithopods begins with a somewhat diagonal margin, followed by an increasingly steepening concave margin. Rhabdodon and higher taxa exhibit surangulars with a concave dorsal margin. Scored as: 1= convex or diagonal; 2= concave in lateral view. 68. Supraoccipital lacks nuchal crest. A sagittal supraoccipital crest unites Iguanodon 167 and Ouranosaurus and has arisen independently in Orodromeus and Tenontosaurus. Scored as: 0= supraoccipital crest: 1= crest absent. 69. Supraoccipital excluded from roof of foramen magnum. Primitively, the supraoccipital occupies a substantial part of the occiput. In higher “iguanodont” taxa, the paraoccipital processes of the opisthotic are greatly enlarged and the supraoccipital is relatively modest. In taxa like Tenontosaurus, Iguanodon and Ouranosaurus, the supraoccipital is reduced to the point it no longer borders the foramen magnum (Norman, 1990 for Iguanodon and higher taxa). Scored as: 0= roofs foramen magnum; 1= Supraoccipital does not roof foramen magnum. 70. Basioccipital with strong ventral keel. In Lesothosaurus and Othnielia the underside of the basioccipital is smoothly rounded. An evolutionary grade from Orodromeus to Dysalotosaurus appears to have developed a ventral keel, being most developed in Zephyrosaurus, Tenontosaurus, Thescelosaurus and Rhabdodon. The character is lost with Camptosaurus and higher taxa. Scored as: 0= no ventral keel; 1= basioccipital keel present. 71. Small percentage of occipital condyle accommodates foramen magnum. In Lesothosaurus, Thescelosaurus, Parksosaurus and Hypsilophodon, the foramen magnum occupies between 30-40% of the dorsal occipital condyle. Othnielia, Orodromeus and Zephyrosaurus possess foramen magnum widths within the occipital condyle 20-30% that of the condyle width. Gasparinisaura and higher taxa have relatively broader basioccipitals and the foramen magnum does not occupy as low of a 168 position within the occiput so the foramen occupies less than 20% of the occipital condyle. Iguanodon is autapomorphic in regard to the foramen magnum occupying over half the dorsal extent of the occipital condyle. Scored as: 1= width of occupied foramen magnum over 30% width of occipital condyle; 2= 20-30%; 3= less than 20% occipital condyle. 72. Floor of basioccipital arched. Unsure as to the significance, the floor of the braincase which lies within the basioccipital is flat in primitive taxa like Lesothosaurus, and basal ornithopods like Othnielia, but arched in Orodromeus, Zephyrosaurus, Thescelosaurus, Parksosaurus, Hypsilophodon and Dysalotosaurus. Tenontosaurus is unique with a concave region here, but all taxa above Tenontosaurus reacquires a flattened surface. Scored as: 0= flat; 1= arched. 73. Median ridge on floor of braincase. A median ridge occurs within the floor of the braincase on the basioccipital in Camptosaurus, Iguanodon and Ouranosaurus. It also occurs in Othnielia. Scored as: 0= no ridge; 1= ridge. 74. Basioccipital tubera level with basisphenoid. Only in Orodromeus, Zephyrosaurus, Thescelosaurus and Camptosaurus do the ventral tubera of the basioccipital meet level with the basisphenoid. In other taxa, the tubera of the basioccipital extend lower then the basisphenoid. Scored as: 0= tubera lower than basisphenoid; 1= level. 75. Basisphenoid longer than basioccipital. Although only limited material has been scored for this feature, there appears a vague grouping based on the relative length of the basioccipital to the basisphenoid. Measured from the base of the parasphenoid process to the posterior edge of the basisphenoid, a ratio to the length of the 169 basioccipital yields Lesothosaurus, Orodromeus and Hypsilophodon with equally long elements. Several higher taxa (Tenontosaurus, Dryosaurusl and Camptosaurus) have longer basioccipitals. In contrast, Zephyrosaurus, Thescelosaurus, Dysalotosaurus, Iguanodon and Ouranosaurus bear longer basisphenoids. Scored as: 0= longer basioccipital; 1= -equal; 2= basisphenoid longer. 76. Cranial nerve V nearly, or completely, enclosed in prootic. Commonly, throughout the analyzed taxa, the prootic is notched on its anteroventral edge by the foramen for trigeminal nerve. Dryosaurus and Dysalotosaurus are united in having a prootic which is enervated further in from the margin by the fifth cranial foramen. In Orodromeus, the same foramen is nearly enclosed but shows no apparent phylogenetic value. Scored as: O= Open; 1= -closed. Postcranial Characters 77. Cervical vertebrae opisthocoelous. Although not found in basal ornithopods, opisthocoely becomes greater developed in the iguanodontian-grade dinosaurs. Modestly opisthocoelous cervical vertebrae occur in Tenontosaurus, Dryosaurus and Dysalotosaurus. Moderate opisthocoely was observed by Sereno (1986) and Norman, (1990) for Camptosaurus and higher taxa, with strong opisthocoely occurring in Iguanodon and higher taxa (Norman, 1990), or Styracosterna (Sereno, 1986). Scored as: 0= plateocoelous to amphicoelous cervical vertebrae; 1= opisthocoelous cervical vertebrae. 78. Spine centered over the dorsal centrum. Primitively within the Ornithopoda, dorsal 170 vertebrae possess spines that arise anteriorly, or over the center of the centrum, migrating progressively backward in posterior dorsal vertebrae. In Tenontosaurus and higher taxa, all dorsal vertebral spines arise posteriorly over the centrum. Scored as: 0= dorsal vertebral spines arise anterior or centered over the centrum; 1= spines posterior. 79. Posterior rib transition. Primitively in Heterodontosaurus and small ornithopod dinosaurs, the point at which the tuberculum and capitulum of the dorsal ribs articulate with the vertebrae, from near vertical to near horizontal, occur within dorsal vertebrae 2- 4. A more posterior transition occurs in Tenontosaurus and higher ornithopod taxa, where the rib attachments change within dorsal vertebrae 5-6. In Ouranosaurus and Iguanodon this transition occurs between dorsal vertebrae 6-8. The significance of this character may be coupled with the positioning of the lungs. Where the ribs articulate to an upper diapophysis and a lower parapophysis the resulting rib movement can only pivot forward, indicating a position forward of the expanding lungs. When this articulating set changes to a more horizontal position, the ribs are allowed to pivot outward, indicating a position lateral to the expanding lungs. Scored as: 1= transition in dorsals 2-4; 2= transition in dorsals 5-6; 3= transition in dorsals 6-8. 80. Sixteen or more dorsal vertebrae. Heterodontosaurus possesses only 12 dorsal vertebrae. Other sister group taxa lack a complete series, so it is unclear as to the primitive count. All small ornithopods above Heterodontosaurus are united by at least 15 dorsal vertebrae. Thescelosaurus and Parksosaurus are united by 16 dorsals. Camptosaurus also possesses 16 dorsals, preparing the way for Ouranosaurus and 'lguanodon which are united by 17. More than 23 pre-sacral vertebrae was a character 171 used by Maryanska & Osmolska (1985) for the Ornithopoda, but this is found in stegosaurids as well. Scored as: 0=12 dorsals; 1=15 dorsals; 2=16 dorsals; 3=17 dorsals. 81. Five to six sacral vertebrae. Heterodontosaurus seems unique in having only four sacrals. Scutellosaurus, Agilisaurus, Yandusaurust and Othnielia possess five sacral vertebrae. Lesothosaurus and the remaining ornithopod taxa analyzed share six sacral vertebrae in the sacrum. Scored as: 1= four sacrals; 2= five sacrals; 3= six sacrals. 82. Tall sacral spines. Although this character is fraught with missing quantified data, a noticeable trend is developed along the cladogram in sacral spine length. Primitively within the group, sacrals tend to have low spines, considerably less than twice the height of the centrum. In Gasparinisaura, Tenontosaurus, Rhabdodon, and Dryosaurust spines measure 2 to 2 1/2 times the height of its centrum. In higher iguanodontian-grade ornithopods, spines measure much greater than 2 1/2 times centrum height. 83. Sacral spines lean somewhat anteriorly. Sacral spines tend to slant slightly posteriorly in most ornithopods. In Camptosaurus and Iguanodont spines lean somewhat forward. Scored 0= posterior; 1= slightly anterior. 84. Pubis articulates with sacrals. The character state is unknown in the sister taxa. Several ornithopod taxa possess a pubis which is only supported by the ilium and ischium. In other taxa, the pubis may be additionally supported medially by a sacral rib. Zephyrosaurus and Orodromeus are united by a pubis with a direct articulation to the first sacral centrum. Scored as: 0= pubis not secondarily supported; 1= pubis supported 172 by sacral rib; 2= pubis supported directly to sacral centrum. 85. Caudal ribs borne on neural arch. In Heterodontosaurus, caudal ribs are borne on the centrum, even in the most anterior caudal vertebrae. Ornithopods in general, possess caudal ribs that originate at the neural-centrum suture. Dryosaurus and Dysalotosaurus bear anterior caudal ribs that originate above the neural-centrum suture, on the neural arch. In more posterior caudal vertebrae, these ribs may originate along the common suture. Scored as: O= caudal ribs from centrum; 1= caudal ribs from neurocentral suture; 2= caudal ribs from neural arch. 86. Ossified hypaxial tendons down tail. Used to diagnose Hypsilophodontidae plus Tenonotsaurus (Sereno, 1986; Norman, 1990; Forster, 1990; Weishampel & Heinrich, 1992), the presence of hypaxial tendons is found here to be less unifying. This character is difficult to score on negative evidence. Although ossified tendons are present along the posterior dorsal and sacral vertebral spines in nearly all ornithopod taxa, irrespective of ontogenetic stage, many specimens do not preserve them. Lack of evidence for hypaxial tendons within the tail of primitive ornithopods may be likewise preservational. Taxa with preserved hypaxial tendons (i.e. Thescelosaurus, Parksosaurus, Hypsilophodon, Gasparinisasura and Tenontosaurus) appear as a grade along the cladogram, subsequently lost in Rhabdodon and higher taxa. Scored as: O= hypaxial tendons absent; 1= hypaxial tendons present. 87. Longest rib on caudal vertebrae posterior of the first. Nearly all the taxa diagnosed in this study possess a tail with caudal ribs which progressively shorten down the tail. 173 Hypsilophodon is unusual in bearing the longest caudal rib on the fifth caudal vertebra. Dysalotosaurus, Camptosaurus and Iguanodon bear their longest caudal ribs on the second tail vertebra. Scored as: 0= First caudal vertebra bears longest rib; 1= Longest rib posterior to first caudal vertebra. 88. Caudal vertebral spines extend beyond own centrum. Ancestrally, the tail spines 1 did not extend posteriorly beyond its own vertebral centrum. All ornithopod taxa exhibit spines which reach over the following vertebra and, except for Parksosaurus and I Rhabdodon, extend past it. Scored as: 0= spines over centrum; 1= spines beyond own centrum. 'I; ‘ j; 89. Scapula with sharp scapular spine. Only in Orodromeus and Zephyrosaurus is the ; anterodorsal spine of the scapula sharply pronounced. Scored as: 0= scapular spine low or broad; 1= scapular spine sharp and pronounced. 90. Short coracoid. Primitively and in general, taxa possess coracoids whose width measures between 70-100% that of the length. Yandusaurusl Rhabdodon, Dryosaurus and Dysalotosaurus have relatively narrower coracoids, less than 60% its length, ■ whereas Iguanodon and Ouranosaurus have coracoids measuring 130% wider than long. Because of the ambiguity of an evolutionary trend, this character was run unordered. Scored as: 1= <60%; 2= 70-100%; 3=130% 91. Coracoid foramen partially open to scapula. Primitively, and commonly among ' i' small ornithopods, the coracoid foramen is located away from the proximal edge, into the body of the coracoid. Tenontosaurus exhibits a borderline example with a foramen 174 closed within the coracoid, but at the edge. In Dryosaurus and higher taxa, the coracoid foramen lies along and enervates the articular surface for the scapula. Scored as: O= foramen closed in coracoid; 1= coracoid foramen open along the coracoid-scapula articular contact surface. 92. Hatchet-shaped sternal. Primitively, sternals are crescent-shaped. In Iguanodon and Ouranosaurus, sternals are broadened proximally but narrow in a ventrolateral process. Scored by Sereno (1986) and Norman (1990) as a synapomorphy for Styracosterna. Scored as: 0= crescent-shaped sternals; 1 = hatchet-shaped sternals. 93. Ulna with high olecranon process. Scutellosaurus, Lesothosaurus, and several basal ornithopod taxa exhibit a relatively low olecranon process on the proximal end of the ulna. Rhabdodon and higher taxa, as well as Hypsilophodon and Orodromeusl possess ulnae with moderately developed olecranon processes. Iguanodon and Ouranosaurus are united as having relatively high olecranon processes. The high olecranon process for Heterodontosaurus is interpreted here as independently derived. Scored as: 0= low olecranon; 1= moderate; 2= high. 94. Cylindrical shaft of ulna. Primitively the shaft of the ulna is triangular or oval in cross section. In Iguanodon and Ouranosaurus, as well as Orodromeus, the ulnar shaft is cylindrical. Scored as: 0= ulna shaft triangular or oval; 1= ulna shaft cylindrical. 95. Ulna bowed. A somewhat bowed ulna appears within a grade of ornithopod taxa above and including Thescelosaurus, but excluding Gasparinisaura, Dryosaurus, Iguanodon and Ouranosaurus. Scored as: 0= straight ulna; 1= ulna bowed. 96. Loss of phalanges on manual digits III, IV and V. Much variation occurs within the 175 phalangeal count of the manus in ornithopods, but due to preservational biases, this character cannot be scored for several taxa. Initial trials of this character were run unordered allowing the distribution within a cladogram to define the subsequent revision of how these are scored. Superimposed on the cladogram a trend is observed with a general step-wise decrease in the number of phalanges in digits III through V. One character used to diagnose lguanodontia, is the loss phalanx on manus digit III (Sereno, 1986; Weishampel & Heinrich, 1992 [although inadvertently described as loss on digit Il]) Iguanodon is unusual in that the trend is broken with the addition of phalanges in digit V (Sereno, 1986 [lguanodontoidea]). Manual formulas were scored as: 0= 2-3-4-S- 0; 1= 2-3-4-2(3)-1; 2= 2-3-4-3-2; 3= 2-3-4-2-2; 4= 2-3-4-2-1; 5= 2-3-3-2-1; 6=2-3-3-2-4; 97. Fused carpus. Defined by Sereno (1986) for Ankylopollexia and Norman (1990) for Camptosaurus and higher taxa, as the parital fusion of the carpals into two blocks: one block consisting of the radiale, intermedium, distal carpals 1 and 3, and metacarpal I; the other block consisting of the ulnare and distal carpals 4 and 5. Personal observation of an unusual instance of fused carpals in young Dryosaurus and an example of unfused carpals in Camptosaurus indicates variation occurs between individuals. The eventual complete fusion of the radiale, distal carpal I, and metacarpal I is defined by Sereno (1986) as diagnostic for lguanodontoidea. Scored as: 0= unfused carpus; 2= fused carpus. 98. Ilium with short and antero-posteriorly long acetabulum. Primitively, ornithopods share an ilium with a relatively high acetabulum. In Orodromeus and in the “iguanodontian-grade” Tenontosaurus and higher taxa, the acetabulum is vertically short 176 and elongate in the sagittal direction. Scored as: 1= high to normal acetabulum; 2= short and long acetabulum. 99. Ischiac peduncle of ilium supported by sacral rib. All ornithopod taxa higher than Heterodontosaurus (?) possess an ilium braced at its ischiac peduncle by a sacral rib. Scored as: 0= no sacral rib attachment; 1= Ischiac peduncle articulates with sacral rib. 100. Bar-like shaft on ischium. Scutellosaurus and Lesothosaurus, as well as most of the primitive members of the Ornithopoda1 possess ischia with a flat blade-like posterior shaft. Diagnosed for Dryomorpha by Sereno (1986), Coria & Salgado (1996) and Salgado & Others (1997), a bar-like ischial shaft would include here Rhabdodon. Scored as: 0= ischium shaft flat and blade-like; 1= shaft bar-like. 101. Distal foot on ischium. An ischium with a distal foot was described for Dryosauridae and higher taxa (Norman, 1984; 1990; Milner & Norman, 1984; Sereno, 1986; Coria & Salgado 1996; Salgado & Others 1997)but is found in Tenontosaurus and Rhabdodon as well. Valdosaurus is unique in this group in lacking a distal foot. Scored as: 0= no foot; 1= foot. 102. Proximally placed obturator process on ischium. A tabular obturator process on ischium is one of the defining characters for the ornithopoda (Norman, 1984; Milner & Norman, 1984; Maryanska & Osmolska, 1985; Sereno, 1986) but is subsequently lost in Rhabdodon. A distally placed obturator process on ischial shaft was used by Weishampel & Heinrich, (1992) to unite Hypsilophodon, Parksosaurus, Zephyrosaurus, and Orodromeus. However, this analysis identifies Parksosaurus and Hypsilophodon with an obturator distal of mid-shaft, while Orodromeus and Thescelosaurus bears an 177 obturator process near mid-shaft. A proximally positioned obturator process near the proximal 40% of the length of the ischium is found in Yandusaurus, Agilisaurus, Othnieiia, Gasparinisaura, Tenontosaurus, and Ouranosaurus. An obturator within the proximal 30% is shared among Dryosaurus and higher taxa (Sereno, 1986; Norman, 1984; 1990; Coria & Salgado 1996; Salgado & Others 1997 ). Run unordered and scored as: 0= no obturator; 1= obturator foramen 60% down shaft of ischium; 2= 50%; 3= 40%; 4= proximal 30%. 103. Iliac peduncle of ischium as large or larger than pubic peduncle. In Lesothosaurus, and common within the basal ornithopods, the iliac peduncle of the ischium is smaller relative to the pubic peduncle. A iliac peduncle as large or larger than the pubic peduncle of the ilium is a synapomorphy for Gasparinisaura and higher taxa other than Dryosauridae. Scutellosaurus and Parksosaurus appear to have independently derived a large iliac peduncle. Run unordered and scored as: 0= pubic peduncle larger; 1= iliac peduncle as large, or larger than pubic peduncle. 104. Anterior process of pubis blade-like. The prepubic process has maintained much attention throughout ornithopod systematics. Its presence partly defines Ornithopoda (Norman, 1984; Milner & Norman, 1984; Sereno, 1986); a rod-shaped prepubic process has been used to define Hypsilophodontia (Sereno, 1986) and the Hypsilophodontidae (Weishampel & Heinrich, 1992; Coria & Salgado, 1996); a laterally flattened anterior ramus used to define Dryosauridae and higher taxa (Norman, 1990); and a transversely flattened and dorsoventrally expanded pre-pubis used to define Iguanodontidae 178 (Sereno, 1986; Milner & Norman, 1984; Norman, 1990). Although the basal ornithopods below Tenontosaurus do exhibit a somewhat rod-like prepubis, they are more flattened transversely in Othnielia, Agilisaurus, Ordromeus and Gasparinisaura that these may be interpreted as sword-like. The pubies for Tenontosaurus and higher taxa all share an expanded anterior ramus, and exaggeratedly so in Ouranosaurus. Scored as: 0= no prepubic process; 1= rod-like, or sword-like prepubis; 2= expanded prepubis. 105. Anterior process of pubis upturned. The anterior ramus of the pubis is up-turned in Agilisaurus, Thescelosaurus, Parksosaurus, Tenontosaurus and higher taxa. Scored as: 0= no prepubic process or straight when present; 1= upturned prepubis. 106. Neck-like constriction under femoral head. All taxa higher than Heterodontosaurus analyzed in this study possesses a neck-like constriction below the femoral head. Scored as: 0= no neck-like constriction; 1= constriction present. 107. Lesser trochanter of femur higher than greater trochanter. This character unites the Dryosauridae and Gasparinisaura. Scored as: 0= lesser trochanter lower or equal to greater trochanter; 1= lesser higher than greater. . 108. Lesser trochanter lateral to greater trochanter on femur. Lesothdsaurus and Scutellosaurus possess large lesser trochanters located somewhat anterior and medial to the greater trochanters. In Heterodontosaurus and all ornithopods, the lesser trochanter of the femur is anterior to, or somewhat lateral to, the greater trochanter. Scored as: 0= lesser trochanter anterior and medial of greater trochanter; 1= lesser trochanter located anterior or somewhat lateral to greater trochanter. 179 109. Greater trochanter of femur laterally flattened. Primitively, the greater trochanter of the femur is laterally convex. Comparatively, in Zephyrosaurus, Thescelosaurus, and Gasparinisaura, the lateral side is slightly flattened, but most extreme in Orodromeus and Parksosaurus. Scored as: 0= greater trochanter convex; 1= flattened. 110. Anterior intercondylar groove on the distal femur present. This character was run L unordered since a modest intercondylar groove occurs in the outgroup taxon, Scutellosaurus. The anterior intercondylar groove has been shown to be a useful character (i.e. Serena, 1986 [Styracosterna]; Norman, 1990 [Dryosauridae +];Milner & Norman, 1984; Weishampel & Heinrich, 1992; Coria & Salgado 1996; Salgado & Others 1997; [lguanodontia]) A modest intercondylar groove is present in Zephyrosaurus (assuming a synonymy with Hypsilophodon weilandi), Thescelosaurus and Fulgerotherium. A well developed anterior intercondylar groove unites taxa above, and including, Tehontosaurus. Scored 0= intercondylar groove absent; 1= modest intercondylar groove; 2= developed intercondylar groove. 111. Low ratio of lateral distal condyle width / medial distal condyle width on femur. Primitively, the outgroup taxa have equally wide distal femoral condyles. All basal ornithopods share a lateral condyle less than 80% the medial condyle width. Ornithopods such as Thescelosaurus and above (excluding Gasparinisaura), have lateral condyles less than 60% medial condyle width. Tenontosaurus shares with higher taxa (excluding Rhabdodon) condyles below the 50th percentile. Ouranosaurus falls under 40%, and Valdosaurus and Iguanodon exhibit lateral condyles less than 30% the width of medial condyles. Scored as: 1= equal (100%); 2 - 80-60%; 3= 59-50%; 4= 49- 180 40%; 5= 39-30%; 6= 29-20%. 112. Proximal condyles on tibia separated by a broad groove. Primitively in Lesothosaurus, Orodromeus and Hypsilophodon, a narrow groove separates the proximal condyles. In heavier animals like Zephyrosaurus, Thescelosaurus, Parksosaurus and Dryosaurus, the condyles are separated by a modestly broad deep groove. In Gasparinisaura and Tenontosaurus, the groove is moderately broad and deep, but noticeably broader in Rhabdodon, Camptosaurus and lguanodon. This character illustrates a trend through ornithopods, but could be linked to increased size. Scored as: 0= narrow groove; 1= modestly broad and deep; 2= moderately broad and deep; 3= very broad groove. 113. Proximal fibular condyle on tibia smaller of the lateral two. Ornithopod taxa above the Orodromeus-Zephyrosaurus clade exhibit small fibular condyles on the proximal end of the tibia. Taxa above Hypsilophodon (excluding Dryosaurus) essentially bear only one lateral condyle. Scored as: 1= both lateral condyles equal in size; 2= fibular condyle smaller; 3= only one lateral condyle on proximal end of tibia. 114. Cnemial crest of tibia bears a well defined edge. Only in the more derived ornithopods analyzed here (lguanodon and Ouranosaurus) is the cnemial crest well defined by a sharp edge. Scored as: 0= rounded cnemial crest; 1= sharply defined. 115. Midshaft of tibia round in cross-section. Camptosaurus, lguanodon and Ouranosaurus share this character. Other taxa exhibit tibia shafts triangular in shape. Scored as: 0= triangular shaft in cross-section; 1= round shaft in cross-section. 181 116. Fibula shaft D-shaped in cross-section. Commonly among ornithopods, the fibula is elliptical or round in cross-section. Zephyrosaurus and Orodromeus are united in a distinct D-shaped fibular shaft. Scored as: 0= absent; 1= present. 117. Astragalus with large ascending process. Common to most ornithopods, are astragali with short ascending processes. Hypsilophodon is somewhat unusual in the ascending process is triangular and tooth-like. In Othnielia, Yandusaurus and Orodromeus, the ascending process is spike-like, being forked in Orodromeus. Relative to ornithopods, Lesothosaurus, Dryosaurus and Dysalotosaurus bear large ascending processes. Scored as: 0= short ascending process; 1 = triangular and tooth-like; 2= spike-like; 3= relatively large ascending process. 118. Astragalus with a high posterior side. The astragalus saddles the distal end of the tibia differently in animals. Irrespective of the ascending process, the astragalus supports better the distal posterior side of the tibia by curling relatively high on the posterior side. This condition is found in Othnielia but unites Rhabdodon and higher taxa. Scored as: 0= low posteriorly; 1= high posterior side. 119. Astragalus with a low anterior side. Although one might assume this character is similar to the previous character, subsequent analyses indicate this feature is uncoupled from the height of the posterior side. Scored as: 0= high anterior side; 1= moderate; 2= low anterior side. 120. Angle between the tibial and fibular articular facets on the calcaneum less then 120 degrees. In most calcania within the taxa analyzed for this character, the angle 182 between the dorsal articular face for the tibia and the anterior contact for the fibula measures greater than 120 degrees. Only in Lesothosaurus, Orodromeus and Zephyrosaurus is this angle considerably less. Scored as: 0= >120 degree angle; 1 = <120 degrees. 121. Medial tarsal round in dorsal view. Throughout most the basal ornithopods, the larger medial tarsal is laterally thin and broadly rectangular dorsally. Heterodontosaurus seems unique in having a blocky, three-dimensional medial tarsal. A scattering of higher taxa (e.g. Gasparinisaura, Rhabdodon1 Iguanodon and Ouranosaurus) possess a medial tarsal round in dorsal view. Scored as: 0= blocky; 1= thin and rectangular; 2= round. 122. Medial tarsal articulates over a portion of the proximal end of metatarsal II. The primitive sister taxa to ornithopods and higher “iguanodontian-grade” ornithopods possess a medial tarsal that covers the proximal end of metatarsal III but fails to extend over the proximal end of metatarsal II. In contrast, the basal “hypsilophodontid-grade” ornithopods from Yandusaurus through Tenontosaurus, and Dryosaurus1 have a medial tarsal that overlaps the lateral or posterior portion of the proximal end of metatarsal II. Scored as: 0= not over metatarsal II; 1= over at least part of metatarsal II. 123. Renifrom lateral tarsal. Although this character suffers from missing data, the available material suggests the lateral tarsal is squared in dorsal view for much of the primitive taxa within the lower half of the cladogram. A lateral tarsal, which caps metatarsal IV, appears kidney-shaped in dorsal view, uniting Orodromeus and Zephyrosaurus, and is common in Hypsilophodon and higher taxa, although 183 Tenontosaurus bears the more primitive squared lateral tarsal. Scored as: 0= square; 1= kidney-shaped. 124. Three functional digits in the pes. Even in Lesothosaurus the pes consists of three primary digits. The fifth digit is reduced to a splint, and the first digit, although functional in movement and in some weight bearing, is much smaller than digits Il through IV. In Gasparinisaura and higher ornithopods, the first digit is reduced to a non-functional splint. This was used by Sereno (1986) to unite the higher Ankylopollexia, probably due to Tenontosaurus having retained a primitive functional first digit. The loss of pes digit V unites Milner & Norman’s (1984) Iguanodontidae and higher taxa, or Sereno’s (1986) lguanodontoidea. Scored as: O= four; 1= three. .$"aL 184 I I i i I I I I i I 2 2 2 2 2 2 2 2 2 2 3 T axon I 2 3 4 5 6 7 8 9 0 I 2 3 4 5 6 7 S 9 0 I 2 3 4 5 6 7 8 9 0 Scu t e l l osaurus ? 7 7 ? 7 7 ? ? 7 ? 7 7 7 7 7 ? 0 0 0 0 ? 7 7 7 7 ? 0 0 7 ? He terodon tosauru ? 0 0 0 i i ? ? 0 ? 0 0 0 0 i 0 7 0 ? 0 ? 0 0 0 2 0 0 0 ? I Leso thosaurus 0 0 0 0 i i 0 0 0 ? 0 0 0 0 i 0 0 0 0 0 0 0 0 0 I 0 0 0 0 0 A g ilis au ru s ? 0 0 I 9 9 ? ? ? ? 7 7 7 0 i 0 ? 7 7 7 ? 0 0 0 2 0 I I 7 ? Vandusaurus 0 7 0 0 I I ? 0 0 ? 7 0 i 0 i 0 7 7 7 0 ? 0 0 0 2 0 7 ? 7 ? O tn ie l ia ? 7 7 7 7 7 ? ? 7 ? 7 7 7 ? 7 7 0 0 0 0 ? 0 0 7 7 0 7 7 7 ? Zephyrosaurus 0 0 i 0 i i I 0 0 I 0 i ? 0 7 7 0 I 0 I 0 0 I 0 ? 0 i 0 i ? Orodromeus 0 0 i 0 i i I I 0 I 0 i 0 0 i 0 0 I 0 I I 0 0 0 ? 0 i I i ? ThesceI osaurus ? 0 i 0 9 2 ? ? I ? 9 i 0 0 i I 0 I 7 0 0 0 I 0 7 0 0 I i 0 Parksosaurus 0 0 i 7 I 2 ? 0 I 0 I 0 0 0’ i 0 0 0 0 0 ? 0 I 0 2 0 7 7 7 0 Bugenosaurua ? 7 7 7 I 7 ? ? 7 ? 7 9 7 7 7 7 7 7 7 0 ? 7 7 7 7 ? i 2 i ? Hypsilophodon 0 0 0 0 I 3 0 0 2 ? 7 0 0 0 i i 0 0 ? 0 0 0 0 0 2 0 i 0 0 0 Tenon tosaurus 0 0 0 0 2 I 0 ? 0 0 0 0 I 0 i i 0 7 7 7 I 0 I 0 2 0 2 2 7 0 Dryosaurus 0 I 2 0 I 3 0 I 0 0 9 0 I I i 0 0 ? 7 0 I 0 0 0 2 0 2 2 0 0 Dysalo tosaurus I I 2 0 I 3 0 I 2 I I 0 I I i 0 0 ? ? ? ? 0 0 0 2 0 2 2 0 I Rhabdodon ? 0 I 0 9 2 0 0 0 0 I 9 ? ? ? ? ? 7 7 7 ? ? ? 9 9 7 2 0 0 ? Iguanodon I I 0 I 2 3 0 I 2 0 I 0 I 0 2 0 I ? i 0 I I I I 3 i 2 2 0 I Ouranosaurus I I 0 I 2 3 0 0 2 ? 7 0 I 0 2 0 I 0 i 0 I I I I 3 i 2 2 0 I Camptosaurus 0 I 7 0 2 3 0 I 2 0 i I I I ? 0 I 0 i 0 I 0 I I 3 0 2 2 0 I Gasparin isaura I 0 0 0 7 3 ? ? 2 ? 7 7 0 0 2 I 7 0 0 0 ? ? 0 0 9 7 ? 7 ? ? Input data matrix (continued) 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 5 5 5 6 Taxon I 2 3 4 5 6 7 8 9 0 I 2 3 4 5 6 7 8 9 0 I 2 3 4 5 6 7 8 9 0 Scu te llosaurus 0 0 7 0 0 0 0 0 0 7 0 7 7 7 7 ? ? 7 7 7 0 0 0 0 0 0 0 I 0 0 Heterodontosauru I I 7 ? I I ? 0 0 ? 0 0 0 i 0 ? ? 0 0 2 0 0 0 I I 0 I 2 0 0 Leso thosaurus 0 0 0 0 0 0 0 I 0 0 0 0 0 0 0 ? ? 0 0 2 0 0 0 0 0 0 0 I 0 0 Agilisaurus 0 I ? 0 0 0 ? I 0 7 0 I ? 0 I ? ? I I I ? ? 7 ? 9 ? 7 ? 7 7 Yandusaurus I I 0 0 0 0 0 I 0 0 0 I I 0 I ? ? ? I I I 0 0 7 0 0 0 2 ? 0 O tn ie lia 0 I 0 0 0 0 7 I 0 7 0 7 7 7 0 ? ? 7 I 7 I 0 0 0 0 0 0 I 0 0 Zephyrosaurus I I 0 0 0 0 2 ? 0 0 0 9 i i I 0 0 0 0 ? ? 0 0 0 0 0 0 I 0 0 Orodromeus 0 I 0 0 0 0 0 0 0 0 0 I i i 0 0 0 0 0 3 2 0 0 0 0 0 0 I 0 0 Thescelosaurus I I 0 0 0 0 0 I 0 0 0 7 i 0 0 ? ? 0 I I 2 0 0 0 0 0 0 I 0 0 Parksosaurus 0 I I 0 0 0 2 I' 0 ? 0 i 0 0 0 ? ? ? I 2 7 0 0 0 0 0 0 I 0 0 Bugenosaurua I I I 0 0 I 2 I 0 ? 0 i 0 0 0 0 ? I ? 2 ? 0 I 0 0 0 0 2 0 0 Hypsilophodon I I 0 0 I I 2 I I 0 0 i 0 0 0 ? ? I I 2 2 0 I I I I 0 I 2 0 Tenontosaurus I I I I I I 2 I I 0 0 i 0 0 0 ? ? I I 2 2 0 0 I I I I 3 2 I Dryosaurus I I I 2 I I 2 I I I I 0 0 0 0 I 0 0 0 2 2 I I I I I I 2 2 I Dysalo tosaurus 9 ? 9 ? 7 7 ? ? 9 ? ? 7 7 0 0 I 0 I 0 2 2 I I I I I I 2 2 I Rhabdodon i I 9 I 9 i 2 I 0 0 0 ? ? ? 7 ? ? ? ? ? I 0 0 I I 0 I 3 2 0 Iguanodon I I I 2 I i 2 ? I I I i ? 0 0 2 I I I 3 4 I I I I I I 4 2 I Ouranosaurus I I O 7 7 7 7 I 7 I 7 0 7 0 0 2 I I I 3 3 I I I 7 7 7 7 2 I Camptosaurus I I i 2 i i 2 I i I i I 0 0 0 0 I I I 2 3 I I I i i i 4 2 I Casparin isaura I I ? 2 i i ? I 7 7 0 I ? 0 0 ? ? I I 2 3 9 9 9 9 7 185 Input data matrix (continued) 6 6 5 6 6 6 6 6 6 7 7 7 7 7 7 7 7 7 7 8 8 8 8 8 8 8 8 8 8 9 Taxon I 2 3 4 5 6 7 8 9 0 I 2 3 4 5 6 7 8 9 0 I 2 3 4 5 6 7 8 9 0 Scutellosaurus 0 7 0 0 0 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 2 ? 7 7 7 0 7 7 0 2 Heterodontosauru 0 i I 0 0 0 i 0 0 7 7 7 7 0 7 0 7 7 i 0 I ? 7 7 0 0 0 0 7 2 Lesothosaurus 0 i 0 0 0 0 i 0 0 0 i 0 7 7 i 0 7 7 7 7 3 ? 7 7 7 0 7 0 7 2 A q ilisaurus ? 7 7 7 I 0 7 7 7 7 7 7 7 7 7 7 7 7 7 I 2 ? 7 7 I 0 7 7 0 7 Vandusaurus I 7 0 7 I 7 7 7 7 7 7 7 7 7 7 7 0 0 i I 2 ? 7 0 I 7 7 I 0 I O tn ie lia I 7 0 0 I 7 7 7 7 0 2 0 i 7 7 7 0 7 7 I 2 I 7 0 I 0 7 I 0 2 Zephurosaurus 7 7 7 7 7 7 7 0 0 I 2 I 0 I 2 0 0 0 i 7 7 ? 7 2 I 0 7 I I 7 Orodromeus i i I 0 I I i I 0 I 2 I 0 I I I 0 0 i i 3 I 0 2 I 0 0 I I 7 ThesceIosaurus i 2 I 0 I I i 0 0 I I I 0 I 2 0 7 0 i 2 3 ? 7 I I 2 0 I 0 2 Parksosaurus 0 2 I 0 I I 7 7 0 7 I I 7 7 7 0 7 0 7 2 3 ? 7 7 I 2 0 I 0 7 Buqenosaurua I 7 I 7 I I 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 ? 7 7 7 7 7 7 7 7 Hqpsilophodon I 2 I 0 I I 7 0 0 i i i 7 0 I 0 7 0 I I 3 I 0 I I 2 i I 0 2 Tenontosaurus 0 I I I I I 7 I I i 3 0 7 0 0 7 i I 2 I 3 2 0 0 I 2 0 I 0 2 Drqosaurus I I I I I 0 2 0 0 i 3 0 0 0 0 I i I 2 I 3 2 0 0 2 0 0 I 0 I DqsaIotosaurus I I I I I I 2 0 0 i 3 I 0 0 2 I I I 7 I 3 ? 0 I 2 0 I I 0 I Rhabdodon I 7 I I I I 2 7 7 i 7 0 0 0 7 7 0 I 7 7 3 2 0 2 I 0 7 I 0 I Iquanodon I 3 0 I I I 2 i i 0 3 0 I 0 2 0 I I 3 3 3 3 I I I 0 I I 0 3 Ouranosaurus I 2 0 0 I I 2 i i 0 I 0 I 0 2 7 7 I 3 3 7 ? 7 7 7 7 7 7 0 3 Camptosaurus I 2 I I I I 2 0 0 0 3 0 I I 0 0 0 I I 2 3 3 i 0 I 7 i I 0 2 Gasparinisaura 7 I I 7 I I I 0 0 0 3 O 9 9 9 9 O 9 9 2 2 0 0 I 2 0 I 0 2 Input data matrix (continued) i I i I I I I I I i I I I I I I I I I I I 9 9 9 9 9 9 9 9 9 0 0 0 0 0 0 0 0 0 0 I I I I I I I I I I 2 Taxon I 2 3 4 5 6 7 8 9 0 I 2 3 4 5 6 7 8 9 0 I 2 3 4 5 6 7 8 9 0 S cu te llosaurus 0 7 0 7 ? 0 0 7 ? 0 0 7 I ? 7 0 0 0 0 I I ? 7 7 ? ? 0 7 7 ? Heterodontosauru 7 ? 2 0 0 2 0 i 7 0 I 0 0 0 0 0 7 I 0 0 I 7 7 0 7 ? 7 7 7 7 Lesothosaurus 0 ? 0 0 0 I 0 i 0 0 0 0 0 0 0 0 0 0 0 0 I I i 7 7 ? 3 7 0 0 Aqi I isaurus 0 ? 7 ? 7 7 7 2 I 0 0 3 7 I I I 0 I 0 7 7 7 7 7 7 ? 0 7 7 7 Vandusaurus 7 ? 0 ? 0 3 0 I I 0 0 3 0 I 0 I 0 I 0 7 3 7 7 7 7 ? 2 0 0 I O tn ie l ia 7 ? 0 ? 0 7 0 I I 0 0 3 0 I 0 I 0 I 0 0 2 ? 7 0 0 ? 2 I 0 I Zephqrosaurus 0 ? 7 ? 7 7 7 7 7 7 7 7 7 7 7 I 0 I I I 2 2 7 7 7 I 0 0 2 0 Orodromeus 0 0 I I 0 7 0 I I 0 0 2 0 I 0 I 0 I I 0 2 I i 0 0 I 2 0 0 0 ThesceI osaurus 0 ? 0 ? I 3 0 I I 0 0 2 0 I I I 0 I I I 3 2 2 0 0 ? 0 0 2 I Parksosaurus 0 0 7 ? 7 7 7 7 I 0 0 I I I I I 0 I I 0 7 2 7 0 7 ? 0 7 0 7 Buqenosaurua 7 ? 7 ? 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 ? 7 7 7 7 Hqpsilophodon i 0 i 0 i 3 0 i i 0 0 i 0 i 0 i 0 i 0 0 3 i 2 0 0 0 i 0 0 i Tenontosaurus 0 0 0 0 i 5 0 2 i 0 I 3 I 2 I i 0 i 0 2 4 3 3 0 0 0 0 0 2 i Drqosaurus I 0 I 0 0 7 I 2 i I I 4 0 2 I i I i 0 2 4 2 2 0 0 ? 3 I 0 i Dqsalotosaurus I 0 I 0 I 7 7 7 7 I I 4 0 2 I i I i 0 2 4 7 7 7 7 ? 3 I ? i Rhabdodon 0 ? I 0 I 7 7 2 I I I 0 I 7 7 i 0 i 0 2 3 4 3 0 0 ? 0 I 2 7 Iquanodon I I 2 I 0 6 i 2 I I I 4 I 2 I i 0 i 0 2 6 4 3 I I ? 0 I 2 7 Ouranosaurus I I 2 I 0 7 i 2 7 I I 3 I 2 0 0 0 i 0 2 5 3 3 I I 0 0 I 2 7 Camptosaurus I 0 I 0 I 2 i 2 i I I 4 I 2 I I 0 i 0 2 9 4 3 0 I 0 0 I 2 7 Gasparin isaura 0 ? 0 ? 0 7 7 I i 0 7 3 I I 0 I I i I. 0 2 3 3 0 0 0 0 0 2 I 186 In p u t d a ta m a tr ix (c o n tin u e d ) 1 1 1 1 2 2 2 2 Taxon I 2 3 4 S cu te llo s au ru s ? ? 7 0 He te rodon tosau ru 0 0 0 0 Lesothosaurus I 0 7 0 A q ilis a u ru s ? 7 7 0 Vandusaurus I i i 0 O tn ie l ia I i i 0 Zephqrosaurus I i 0 0 Orodromeus I i 0 0 ThesceIosau rus I i 0 0 Parksosaurus I 7 7 0 Buqenosaurua ? 7 7 7 Huipsi lophodon I i i 0 Tenontosaurus I i 0 0 Druosaurus I i I I D usa lo tosaurus 7 0 7 I Rhabdodon 2 0 i I Iquanodon 2 0 i I Ouranosaurus 2 7 7 I Camptosaurus 7 0 7 I G asoa rin is au ra 2 I i I