DISSERTATION RESEARCH: Extinction and Diversification Dynamics of Archosauria Through Early Mesozoic Climate Crises

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Two mass extinctions occurred early in the Mesozoic Era shortly after dinosaurs appeared, and multiple lines of evidence suggest that dramatic global climate change events were contributing factors. This project will investigate the response of the extinct relatives of birds and crocodilians (the Archosauria) to these episodes. The primary objectives of this study are to analyze the evolutionary relationships of fossil archosaurs, and use these evolutionary relationships as a framework to investigate how archosaur respiratory anatomy and body temperature regulation changed after the extinctions at the end of the Triassic Period and during the Early Jurassic Epoch. The study will test the hypothesis that global warming events initiated evolutionary changes in respiratory anatomy and contributed to currently unexplained patterns of extinction and diversification of extinct archosaurs, including dinosaurs. This research will provide insight into the ways that vertebrate communities on land respond to rapid changes in climate, and may help to predict which species will experience an increased risk of extinction during modern climate change. This research will provide multiple opportunities for undergraduate training. In addition, educational materials based on the results will be distributed to educators at secondary and higher education levels, as well as disseminated in the form of scientific papers and presentations at professional meetings.Time-calibrated phylogenies of Archosauria will be estimated using both parsimony analyses of morphology and combined-evidence Bayesian approaches to phylogeny reconstruction incorporating molecular sequence data from extant archosaurs. Character transformation rates for respiratory-related characters (e.g. postcranial skeletal pneumaticity) and non-respiratory characters will be modeled iteratively over a large sample of time-calibrated trees to account for uncertainty in phylogeny and chronology. Non-parametric statistics will be used to test for the presence of rate-shifts in respiratory character evolution surrounding the interval of extinctions and associated climate changes in the early Mesozoic Era.