Theses and Dissertations at Montana State University (MSU)
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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 Osteohistology of sutural fusion in the skulls of Archosaurs: implications for maturity assessment in non-avian dinosaurs and for the evolution of skeletal tissues(Montana State University - Bozeman, College of Letters & Science, 2015) Bailleul, Alida Mehiti; Chairperson, Graduate Committee: John R. Horner; John B. Scannella, David C. Evans and John R. Horner were co-authors of the article, 'Ontogeny of sutural closure in the skulls of extant archosaurs: reconsidering maturity assessment in non-avian dinosaurs' which is contained within this thesis.; John R. Horner was a co-author of the article, 'Comparative histology of some craniofacial sutures and skull-base synchondroses in non-avian dinosaurs and their extant phylogenetic bracket' which is contained within this thesis.; Brian K. Hall and John R. Horner were co-authors of the article, 'First evidence of dinosaurian secondary cartilage in the post hatching skull of Hypacrosaurus stebingeri (Dinosauria, Ornithischia)' in the journal 'PLoS ONE' which is contained within this thesis.; Brian K. Hall and John R. Horner were co-authors of the article, 'Secondary cartilage revealed in a non-avian dinosaur embryo' in the journal 'PLoS ONE' which is contained within this thesis.; Catherine Nyssen-Behets, Benoit Lengele, Brian K. Hall, John R. Horner were co-authors of the article, 'Chondroid bone in dinosaur embryos and nestlings (Ornithischia: Hadrosauridae): insights on the growth of the skull and the evolution of skeletal tissues' in the journal 'Comptes Rendus Palevol' which is contained within this thesis.Sutures are fibrous tissues that unite the skull bones of vertebrates. The degree of sutural closure is often used in paleontology to assess maturity in mammals and dinosaurs. Surprisingly, little is known about the biology of sutures in the closest evolutionary groups to non-avian dinosaurs: birds and crocodilians (extant archosaurs). The purpose of this dissertation is to assess, by means of morphological observations, if the degree of sutural closure is indeed an accurate method for maturity assessment in non-avian dinosaurs, and to gain a better understanding of archosaurian sutures at the microscopic scale. The order in which sutures fuse in the skulls of emus (n=24) and American alligators (n=50) reveals that sutural closure is a useful proxy for maturity in the former species but not in the latter. As growth progresses in alligators, sutures become relatively wider and more open in larger, older individuals compared to smaller, younger specimens. This pattern is previously unreported in alligators and it likely reflects skull mechanics related to feeding and not exclusively ontogeny. This indicates sutural closure is not a robust proxy for maturity in non-avian dinosaurs. Next, the histology of craniofacial sutures in these same extant species and in some non-avian dinosaurs is studied. Comparisons with mammalian sutural histology from the literature are also made. Emus and mammals possess a sutural periosteum, but it disappears rapidly during ontogeny in American alligators. The histology of the sutural mineralized tissues of non-avian dinosaurs suggest that they also lack a sutural periosteum and that their primary mode of ossification involves the direct mineralization of the fibrous soft-tissues of their sutures. The microstructural differences between sutures in archosaurs and mammals are undeniable, indicating that extant mammals are a poor analogue for investigating the growth of non-avian dinosaurs. Finally, the sutural borders of embryonic and nestling hadrosaurs are investigated. They are composed of chondroid bone, a tissue that allows rapid sutural growth in some extant species, but these sutural mineralized fronts lack secondary cartilage. Instead, secondary cartilage was only observed at jaw articulations. This tissue is found exclusively in birds within extant sauropsids, reflecting the dinosaurian origin of birds.Item Frequency response analysis of the in-vivo human skull(Montana State University - Bozeman, College of Engineering, 1977) Grammens, Gerald Martin