Theses and Dissertations at Montana State University (MSU)
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Item The evolution of facial keratin and tooth distribution: implications for the coevolution of traits in dinosaurs(Montana State University - Bozeman, College of Letters & Science, 2021) Aguilar-Pedrayes, Isaura; Chairperson, Graduate Committee: David VarricchioResearch on birds indicates that the occurrence of beak keratin and teeth are mutually exclusive, and both traits are widely distributed across Dinosauria. The macroevolution of the antagonistic relationship between keratinous beaks and teeth has only recently been explored, and these studies focus on Aves and non-avian Coelurosauria. Currently, many hypotheses posit an adaptive advantage for the trade-off of these two traits but have not been tested on a macroevolutionary scale. Examples in non-coelurosaurian dinosaurs and non-adaptive alternatives, such as trait evolution correlation and phylogenetic history, have yet to be explored thoroughly-. This study assesses the current evolutionary assumptions of beak-like keratin and tooth distribution across dinosaurs using recently-developed variable rate phylogenetic comparative methods. The diagnostic bone surface used as a proxy for the keratin cover in fossil jaws is smooth grooved textures with foramina at the jaw tips. The effect of a keratin cover on the tooth distribution within individuals is tested with Markov Chain Monte Carlo (MCMC) multinomial regression models. Coevolutionary rates for these structures are evaluated with Bayesian RJ-MCMC algorithms. The best-fit model is determined using Bayes Factors. The taxonomic breadth increased the evolutionary sample size and thus analytical power but forced a simplified coding scheme for beak and tooth traits. My analysis shows that the presence of a keratin cover influences the evolution of partial toothrow reduction but not complete tooth loss. Another factor could have driven the evolution of toothless beaks in some dinosaurs. In addition, the evolution of a reduced toothrow only precedes the presence of a keratin cover in the Theropoda lineage. Furthermore, the evolutionary rate of toothrow distribution was higher and more diverse when a keratin cover was absent; this suggests that the keratin cover imposes a functional constraint on tooth diversity at macroevolutionary scales.Item Analysis of hadrosaur teeth from Egg Mountain Quarry, a diffuse microsite locality, upper Cretaceous, Two Medicine Formation, northwest Montana(Montana State University - Bozeman, College of Letters & Science, 2018) Scofield, Garrett Benson; Chairperson, Graduate Committee: David J. VarricchioEgg Mountain locality as part of the Willow Creek Anticline in the Upper Cretaceous Two Medicine Formation of northwest Montana has become well known for its preservation of dinosaur eggs, eggshell, nesting traces, insect traces and more recently described mammals and lizards. The diffuse micro-vertebrate locality also turns up an abundance of hadrosaur and theropod teeth. Population dynamics of dinosaurian taxa are known though analysis of long bone material and histology. Here we test the utility of hadrosaur teeth for the same means. Field excavations of a new Egg Mountain Quarry from 2010-2015 resulted in the collection of 564 hadrosaur tooth fragments presumed to belong to Maiasaura peeblesorum in addition to a variety of theropod teeth. The most complete Maiasaura teeth were measured and compared to Maiasaura specimens from museum collections. A subset of the Egg Mt. assemblage was subjected to histological analysis as means to understand tooth formation and shedding rates. Unique factors were developed and applied to the assemblage translating tooth abundance into an abundance of individuals and ultimately mortality and survivorship. Analysis of museum collections and Egg Mt. hadrosaur teeth revealed high proportions of juvenile individuals as part of the abraded and largely incomplete Egg Mt. specimens. High mortality rates occur within the first year of life followed by a marked decrease until adult age and size is attained. Seasonal nesting grounds and a seasonal and semi-arid environment proposed for the Egg Mt. area is supported by high proportions of young individuals. Individuals gathering at ephemeral ponds and lakes, including identified theropod taxa, promote a concentration of shed and disarticulated teeth in conjunction with autochthonous mammal, lizard, and dinosaur nesting material. Ontogenetic changes in hadrosaur teeth and the conditions of the Egg Mt. assemblage complicate what an individual tooth represents; however, shed and disarticulated hadrosaur teeth appear to show effectiveness in paleoecological population studies. Continued work on abundant dinosaur tooth assemblages would hone these new techniques and potentially provide insight into similar microsite assemblages around the world.Item Pattern correlation of mammalian teeth as a means of identification(Montana State University - Bozeman, College of Agriculture, 1939) Buck, Charles L.Item Verification of von Ebner incremental lines in extant and fossil archosaur dentine and tooth replacement rate assessment using counts of von Ebner lines(Montana State University - Bozeman, College of Letters & Science, 1992) Erickson, Gregory Mark