Scholarship & Research
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/1
Browse
4 results
Search Results
Item Ontogenetic and stratigraphic cranial variation in the ceratopsid dinosaur 'Triceratops' from the Hell Creek Formation, Montana(Montana State University - Bozeman, College of Letters & Science, 2015) Scannella, John Benedetto; Chairperson, Graduate Committee: John R. Horner; John R. Horner was a co-author of the article, 'Torosaurus marsh, 1891 is Triceratops marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontoge' in the journal 'Journal of vertebrate paleontology' which is contained within this thesis.; John R. Horner was a co-author of the article, ''Nedoceratops: an example of a transitional morphology' in the journal 'Public library of science ONE' which is contained within this thesis.; Denver W. Fowler was a co-author of the article, 'A stratgraphic survey of Triceratops localities in the Hell Creek Formation, northeastern Montana (2006-2010)' in the 'Geological Society of America Special Paper 503' which is contained within this thesis.; Denver W. Fowler, Mark B. Goodwin and John R. Horner were co-authors of the article, 'Evolutionary trends in Triceratops from the Hell Creek Formation, Montana' submitted to the journal 'Proceedings of the National Academy of Sciences of the United States of America' which is contained within this thesis.; David W. Roberts and John R. Horner were co-authors of the article, 'A morphometric analysis of casque development and variation in the black-casqued hornbill (Ceratogymna atrata)' which is contained within this thesis.; Kristopher J. S. Purens and John R. Horner were co-authors of the article, 'A morphometric analysis of trends in cranial morphology in Triceratops and 'Torosaurus' from the Hell Creek Formation, Montana' which is contained within this thesis.Hypotheses regarding the taxonomy and systematics of non-avian dinosaurs are based on analyses of morphology. As such, it is critical to assess the potential roles of intraspecific variation in systematic interpretations. Ontogenetic (developmental) change has been found to be a potential contributor to taxonomic confusion in the fossil record of dinosaurs. Similarly, variation between specimens found at different stratigraphic levels should be assessed in order to decipher variation within and between closely related taxa. The chasmosaurine ceratopsid Triceratops has had a complicated taxonomic history due to variation in cranial morphology between specimens. Recent work in the uppermost Cretaceous Hell Creek Formation (HCF) has produced a large (n>50) new sample of specimens. Using this data set its possible to reassess variation in Triceratops and further explore chasmosaurine paleobiology. Building on previous work on Triceratops ontogeny, examination of the parietal-squamosal frill finds that these bones underwent a dramatic transformation late in ontogeny. The short, solid frill of Triceratops expanded into a more elongate, thin, fenestrated condition, which had previously been found to characterize the coeval ceratopsid taxon Torosaurus latus. This suggests that these taxa are synonymous with Torosaurus representing the mature form of Triceratops rather than a distinct taxon. Further, Nedoceratops hatcheri, which is represented by a single specimen with a small fenestra in the parietal, is hypothesized to represent a transitional morphology between unfenestrated and fully fenestrated (Torosaurus) specimens. Detailed locality information for specimens collected over the course of the Hell Creek Project permits for the placement of specimens in stratigraphic context. The two currently recognized species, T. horridus and T. prorsus, are stratigraphically separated within the HCF and cladistic and stratocladistic analyses are consistent with the evolution of Triceratops incorporating anagenetic (transformational) change. Morphometric analyses of the extant archosaur Ceratogymna atrata (the Black-casqued hornbill) indicate that enlarged cranial structures function as objects of visual display. Morphometric studies of Triceratops further suggest that specimens found lower in the formation may have attained the Torosaurus frill morphology through ontogeny, whereas this basal condition became increasingly rare higher in the formation. Morphometric results are also consistent with early divergence between two distinct genera.Item A new multi-faceted framework for deciphering Diplodocid ontogeny(Montana State University - Bozeman, College of Letters & Science, 2015) Woodruff, David Cary; Chairperson, Graduate Committee: John R. Horner; Denver W. Fowler and John R. Horner were co-authors of the article, 'A new multi-faceted framework for deciphering Diplodocid ontogeny' which is contained within this thesis.Since sauropod dinosaurs lack the extravagant cranial features that are important to tracking ontogenetic trajectories (changes through growth), sauropods generally garner less focus on development than those dinosaurs with expressive cranial displays. The apparent lack of features that radically change through ontogeny has even led some to speculate that sauropods exhibited isometric growth. Yet within the past decade a small number of morphologic features have been demonstrated to undergo significant morphologic change; thus maturity can be tracked in ways other than histologic analysis (bone microstructure). The recognition of features that change dramatically through ontogeny hints at significant phylogenetic and biomechanical consequences in the immature sauropod condition. However the topic of morphologic ontogenetic change in sauropods is highly debated, with some question as to the validity of these apparent patterns. The current study will attempt to recognize additional morphologic and histologic features that can be used to infer maturity in diplodocid sauropods. By examining a broad range of features that span every aspect of the skeleton, the goal of this analysis is to substantiate previous ontogenetic inferences and conclusions. The findings of this analysis indicate that contrary to previous notions, diplodocid sauropods underwent radical ontogenetic changes in several skeletal elements. This analysis also establishes a suite of morphologic and histologic attributes that in combination can be used as a guide to identify maturational status in other diplodocid specimens. In addition this study also raises question to the validity of small bodied sauropod specimens that were previously recognized as distinct species.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 Multivariate analysis of avian and non-avian theropod pedal phalanges(Montana State University - Bozeman, College of Letters & Science, 2008) Kambic, Robert Emmett; Chairperson, Graduate Committee: David VarricchioThe relationship between morphology and behavior in theropods was examined using multivariate analyses performed on a set of linear measurements of pedal non-ungual phalanges in a sample of 132 extant and 13 extinct taxa. Principal component analysis reveals that modern birds with terrestrial lifestyles tend to cluster away from those with raptorial and non-predatory grasping lifestyles although the division is not clean. Most non-avian dinosaurs tend to cluster with terrestrial species although Deinonychus and some Tyrannosaurids cluster with raptorial taxa. Terrestrial taxa tend to have phalanges that are comparatively shorter distally, are relatively wide, and have shallow grooving of the distal trochleae, while grasping taxa show opposing trends. Predatory graspers have proportionately wider phalanges than non-predatory graspers. Discriminant function analysis performs well in distinguishing among species with specialized behavior while taxa with less stereotyped behaviors are harder to classify. Predatory graspers are easily separated from non-predatory graspers. Troodon and Elmisaurus are grouped with terrestrial/cursorial taxa. Tyrannosaurus, Allosaurus, Daspletosaurus, and Albertosaurus are identified as terrestrial/cursorial with some possible predatory grasping ability. Deinonychus and Bambiraptor appear to have more grasping ability than Troodon.