Theses and Dissertations at Montana State University (MSU)
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Item Osteology, phylogeny, taphonomy, and ontogenetic histology of Oryctodromeus cubicularis, from the middle Cretaceous (Albian-Cenomanian) of Montana and Idaho(Montana State University - Bozeman, College of Letters & Science, 2017) Krumenacker, L. J.; Chairperson, Graduate Committee: David Varricchio; David J. Varricchio, Chris Organ, Clint Boyd and Brooks Britt were co-authors of the article, 'Osteology and phylogeny of the neornithischian dinosaur Oryctodromeus cubicularis from the middle Cretaceous (Albian-Cenomanian) of Montana and Idaho' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this thesis.; David J. Varricchio, John Wilson and Ashley Ferguson were co-authors of the article, 'Taphonomy of Oryctodromeus cubicularis from the mid-Cretaceous (Albian-Cenomanian) of Idaho, and additional Oryctodromeus burrows from Idaho and Montana' submitted to the journal 'Palaeogeography, palaeoclimatology, palaeoecology' which is contained within this thesis.; David J. Varricchio, John R. Horner and Kelli Taddy were co-authors of the article, 'Ontogenetic histology and growth of the neornithischian dinosaur Oryctodromeus cubicularis from the middle Cretaceous (Albian-Cenomanian) of Montana and Idaho' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this thesis.Oryctodromeus is a small bipedal dinosaur known from middle Cretaceous (95-100 My) Wayan Formation of Idaho and the Vaughn Member of the Blackleaf Formation of Montana. This taxon is hypothesized to be a burrowing dinosaur, which cared for its young within these burrows. This dissertation is a broad three-part treatment of this taxon, and excepting the introductory and concluding chapters this dissertation consists of three main chapters. Chapter two describes the osteology and phylogenetic relationships of this animal. Notable features of the Oryctodromeus skeleton described include a network of ossified tendons along the vertebral column that completely ensheath the tail, a long tail that forms more than half the length of the animal, and unusual femoral heads whose morphology may be related to burrowing behavior. The first full skeletal and skull reconstructions of this animal are presented. Chapter three investigates patterns of preservation of Oryctodromeus. Data suggests that preservation of single to multiple individuals of this taxon typically occurred in burrows that may be difficult to impossible to recognize in the fossil record. New examples of burrows from Oryctodromeus from the Vaughn and Wayan, as well as additional evidence for social behavior, are also described. A third chapter details the ontogenetic histology, growth rates and patterns of skeletal fusion based on seven limb elements (femora and tibiae) from different individuals. Based on the data in this dissertation, three growth stages can be recognized in Oryctodromeus based on bone histology. Juveniles are defined by more rapidly growing fibrolamellar tissue, sub-adults are defined by a cortex of inner fibrolamellar tissue and outer zonal parallel fibered tissue, and near-adult individuals have tissue similar to sub adults with dense avascular bone in the outermost cortex that signals a decrease in growth rate. LAG's suggest a minimum age of six to seven years for more mature individuals. Patterns of neurocentral fusion in Oryctodromeus appear similar to those of crocodylians and some other small ornithischians, while the growth rates of Oryctodromeus appear slower than those of some dinosaurs, but similar to taxa such as Orodromeus and Tenontosaurus.Item Histovariability and growth in the basal ceratopsian dinosaur Psittacosaurus mongoliensis from the lower Cretaceous Khulsangol Formation, central Mongolia(Montana State University - Bozeman, College of Letters & Science, 2016) Zorigt, Badamkhatan; Chairperson, Graduate Committee: David Varricchio; John R. Horner (co-chair); John R. Horner and Khatanbaatar Purevdorj were co-authors of the article, 'Taphonomy and depositional environment of a monodominant Psittacosaurus bonebed from the lower Cretaceous Khulsangol Formation of central Mongolia' submitted to the journal 'Journal of vertebrate paleontology ' which is contained within this dissertation.; John R. Horner was a co-author of the article, 'Intraskeletal histovariability in the hind limb of Psittacosaurus mongoliensis' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this dissertation.; John R. Horner was a co-author of the article, 'Ontogenetic histovariability in a population of Psittacosaurus mongoliensis from the lower Cretaceous Khulsangol Formation, Uvurkhangai Province, Mongolia' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this dissertation.Large datasets are required in order to study the details of growth in non-avian dinosaurs. The Cretaceous dinosaur sites in Mongolia offer tremendous opportunities to collect a sufficient data for such study. This dissertation introduces a brief history of dinosaur research in Mongolia. As a result of many expeditions since the 1920s, numerous new dinosaurs were named and many new dinosaur localities have been discovered. Whereas the majority of studies of Mongolian dinosaurs have focused on the fossils of Late Cretaceous taxa, dinosaur fossils are also abundant in the Early Cretaceous dinosaur sites. One of the richest Early Cretaceous dinosaur sites is Builst Khudag (BLK) in central Mongolia. Sedimentologic and taphonomic studies of the BLK site suggest that the depositional environment of the locality indicates the occurrence of a debris flow and sheet-flood in an alluvial setting. The fossils of the parrot-beaked, herbivorous dinosaur Psittacosaurus is the most common taxon from the BLK site. A Psittacosaurus aggregation consisting of juveniles reflects a catastrophic mortality event. Previously, the humerus, femur, tibia, and fibula were suggested to represent the ideal bones for growth determination studies. Since various elements grow in different developmental regimes, it is necessary to further determine an ideal element for Psittacosaurus growth assessment. Associated femora, tibiae, and fibulae from four individuals were examined. The femur and tibia show comparable bone tissues in all individuals; the tibia and fibula present comparable numbers of growth lines. Based on this finding, the tibia appears to provide the most comprehensive view of growth in Psittacosaurus. The Psittacosaurus growth strategy was further assessed using 58 tibiae collected from the BLK site. The Psittacosaurus growth rate reaches its peak (3.19 microns/day) after passing the threshold size at the age of two. During the ages of 10-13, the body size reaches 170.3 cm in length and the growth rate is considerably slowed down. This study confirms that Psittacosaurus growth fits in a sigmoidal shaped curve.Item Evolution and ontogeny of Hadrosaurs (Dinosauria: Ornithischia) in the Judith River Formation (late Cretaceous: Campanian) of northcentral Montana(Montana State University - Bozeman, College of Letters & Science, 2015) Freedman, Elizabeth Anne; Chairperson, Graduate Committee: John R. Horner; John R. Horner was a co-author of the article, 'A new brachylophosaurin hadrosaur (Dinosauria: Ornithischia) with an intermediate nasal crest from the Campanian Judith River Formation of northcentral Montana' submitted to the journal 'PLoS One' which is contained within this thesis.; John R. Horner was a co-author of the article, 'A new species of Gryposaurus (Dinosauria: Ornithischia) from the Judith River Formation of northcentral Montana' which is contained within this thesis.Hadrosaurs, the 'duck-billed' dinosaurs, were abundant members of Campanian (Late Cretaceous) communities in the Western Interior of North America, and are thus an ideal group for studying high-resolution evolutionary trends. This dissertation describes two new hadrosaurine taxa from the Judith River Formation exposed in Kennedy Coulee, northcentral Montana. The localities are stratigraphically equivalent to Unit 1 of the Oldman Formation, a time interval with no previously described hadrosaurine species. Phylogenetic and geometric morphometric analyses, combined with recalibrated radiometric dates, demonstrate that the new taxa form morphologic and stratigraphic intermediates within the lineages of Gryposaurus and Acristavus-Brachylophosaurus. The new genus of brachylophosaurin has a short posteriorly-oriented nasal crest hypothesized as an intermediate evolutionary state between the stratigraphically lower crestless Acristavus (lower Two Medicine Formation) and the stratigraphically higher Brachylophosaurus (middle Oldman Formation), with its wide posteriorly elongated crest. The nasal crest of Brachylophosaurus elongates posteriorly ontogenetically (as the individual grows). Histologic analysis demonstrates that the holotype of the new genus is relatively more mature than the largest Brachylophosaurus specimen, so its smaller crest size is not due to the ontogenetic status of the holotype. The new species of Gryposaurus is from a monodominant bonebed of at least ten individuals and three size classes: juvenile, subadult, and adult. The taphonomy of the bonebed is interpreted as a mass death assemblage deposited along a lake margin. The abundant postcranial bones are illustrated in a photographic atlas. In the new Gryposaurus species, the shape and position of the nasal crest is morphologically intermediate between the stratigraphically lower G. latidens (lower Two Medicine Formation) and the stratigraphically higher G. notabilis (lower Dinosaur Park Formation). In G. latidens, the nasal crest is low and anterodorsal to the posterior narial fenestra. The nasal crest becomes progressively higher and more posteriorly located in stratigraphically younger species. A similar trend occurs ontogenetically within specimens of the same species. Thus, in Gryposaurus and Acristavus-Brachylophosaurus lineages, directional trends in nasal crest morphology are observed both through ontogeny and between stratigraphically separated non-overlapping taxa, suggesting that the new taxa may be transitional members of anagenetic evolutionary lineages.Item Scratch-digging in the Cretaceous basal ornithopod dinosaur Oryctodromeus cubicularis : evidence from morphometric analyses and reconstruction of the forelimb musculature(Montana State University - Bozeman, College of Letters & Science, 2013) Fearon, Jamie Lynn; Chairperson, Graduate Committee: David Varricchio; David J. Varricchio was a co-author of the article, 'Morphometric analysis of the forelimb and pectoral girdle of the Cretaceous ornithopod dinosaur Oryctodromeus cubicularis and implications for digging' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this thesis.; David J. Varricchio was a co-author of the article, 'Reconstruction of the forelimb musculature of the Cretaceous ornithopod dinosaur Oryctodromeus cubicularis: implications for digging' submitted to the journal 'Journal of vertebrate paleontology' which is contained within this thesis.The basal ornithopod dinosaur Oryctodromeus cubicularis was discovered within a burrow structure in the mid-Cretaceous Blackleaf Formation of western Montana. This, and features of the pelvis, skull, and forelimbs also seen in burrowing mammals led to the interpretation of Oryctodromeus as the first formally described burrowing dinosaur. This study further describes the forelimb specialization of Oryctodromeus and analyzes the validity of the interpretation of Oryctodromeus as adapted for digging using morphometric analyses and muscular reconstructions of the humerus, scapula, and coracoid. The morphometric analyses used two methods, including traditional morphometrics using principal component analysis of a series of element length measurements and geometric morphometrics using relative warp analysis of a series of landmarks superimposed on photographs of elements. Both methods reduce the number of variables to explain the greatest amount of variation between specimens. Results indicated that the humerus of Oryctodromeus is slightly more robust than other basal ornithopods, the coracoid exhibits no specialization for digging, and the scapula is strongly specialized, with a long narrow acromion and strongly expanded posteroventral margin of the scapular blade providing greater surface area for muscle attachment. Reconstruction of the forelimb musculature was generated by comparing both the presence or absence of muscles and the locations of attachment sites between birds and crocodilians, the extant phylogenetic bracket of dinosaur, and by examination of specimens of Oryctodromeus and other ornithopods for osteological correlates. Muscle groups used for burrowing in mammals include the deltoideus scapularis, latissimus dorsi, triceps longus, and teres major. The first three are present in Oryctodromeus, but the presence of the teres major is equivocal. The strongly expanded posteroventral scapula indicates an increased surface area for the origin of the deltoideus scapularis and possibly teres major. This expanded area would be advantageous for burrowing. The origin of the triceps longus near the glenoid of the scapula would not provide strong extension of the antebrachium, a motion important in scratch-digging. The osteology and musculature both provide evidence of slight adaptation for scratch-digging in Oryctodromeus. As many vertebrates burrow without morphological specializations, the presence of these features sufficiently supports adaptation for burrowing in Oryctodromeus.