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

在恐龙出现后不久的中生代早期发生了两次大灭绝，多种证据表明，剧烈的全球气候变化事件是促成灭绝的因素。该项目将调查鸟类和鳄鱼的灭绝近亲（始祖目）对这些事件的反应。本研究的主要目的是分析化石祖龙的进化关系，并以此为框架研究在三叠纪末和早侏罗世灭绝后，祖龙的呼吸解剖结构和体温调节是如何变化的。这项研究将验证一个假设，即全球变暖事件引发了呼吸解剖学的进化变化，并导致了包括恐龙在内的已灭绝的始祖恐龙目前无法解释的灭绝模式和多样化。这项研究将深入了解陆地上的脊椎动物群落对气候快速变化的反应方式，并可能有助于预测在现代气候变化中哪些物种将面临更大的灭绝风险。本研究将为本科生的培养提供多种机会。此外，根据调查结果编写的教育材料将分发给中等和高等教育的教育工作者，并以科学论文和在专业会议上发言的形式散发。我们将利用形态学的简约分析和结合现存祖龙分子序列数据的系统发育重建的联合证据贝叶斯方法，对祖龙的时间校准系统发育进行估计。呼吸相关特征（如颅后骨骼肺炎）和非呼吸特征的特征转换率将在时间校准树的大样本上迭代建模，以考虑系统发育和年代学的不确定性。非参数统计将用于测试中生代早期灭绝间隔和相关气候变化中呼吸特征进化中速率变化的存在。

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.