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

在中生代早期恐龙出现后不久发生了两次大规模灭绝，多条证据表明，剧烈的全球气候变化事件是促成因素。这个项目将调查鸟类和鳄鱼的灭绝亲属（初龙类）对这些事件的反应。本研究的主要目的是分析古龙类化石的演化关系，并以此为框架，探讨三叠纪末和早侏罗世古龙类呼吸解剖和体温调节的变化。这项研究将检验一个假设，即全球变暖事件引发了呼吸解剖学的进化变化，并导致了目前无法解释的灭绝模式和包括恐龙在内的已灭绝主龙的多样化。这项研究将深入了解陆地上脊椎动物群落对气候快速变化的反应方式，并可能有助于预测哪些物种在现代气候变化期间将面临更大的灭绝风险。这项研究将为本科生培训提供多种机会。此外，教育材料的基础上的结果将分发给教育工作者在中等和高等教育水平，以及传播的形式的科学论文和演示文稿在专业会议。时间校准的始祖龙类的生殖将估计使用两个简约分析的形态和组合证据贝叶斯方法结合分子序列数据从现存的始祖龙类的生殖重建。将在大量时间校准树样本上迭代建模与呼吸相关的特征（例如，颅后骨骼的不稳定性）和非呼吸特征的特征转换率，以考虑发育和年代学的不确定性。非参数统计将被用来测试周围的呼吸特征演变的间隔和相关的气候变化在中生代早期的速率变化的存在。

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.