DISSERTATION RESEARCH: The early evolution and adaptive radiation of saurian reptiles

爬行动物是现代生态系统的重要组成部分，已知物种超过20，000种。化石和分子证据表明，所有这些活的物种都属于一个单一的群体，蜥蜴，它起源于2.6亿年前的二叠纪时期。虽然蜥蜴类在二叠纪化石记录中很罕见，但在2.52亿年前二叠纪末的一次大规模灭绝事件后，它们变得普遍而多样。二叠纪末的物种灭绝发生在大规模火山爆发和海洋酸化的同时，估计有95%的物种生活在当时。灭绝后出现的蜥蜴类很快就进化出了令人难以置信的身体大小、体型和饮食多样性，这表明它们利用了灭绝造成的生态系统中的许多空白。然而，对最古老的蜥蜴类的家谱知之甚少，关于所有现代爬行动物祖先的关键问题仍然没有答案：在二叠纪末的环境变化期间，蜥蜴类的多样性是如何变化的？早期蜥脚类动物在解剖学上的变化有多快？所有现存爬行动物的祖先是什么样子的，我们今天看到的血统是如何从那个祖先改变的？研究这些问题将使科学家们能够了解今天发生的类似环境变化对现存动物物种的影响。它还将为我们在更严重的环境危机之后可能预期的变化提供一个基线。二叠纪和三叠纪时期的化石太古老了，无法保存DNA，重建它们的进化历史必须依靠详细的解剖研究。不幸的是，大多数早期蜥蜴类的解剖结构还没有得到很好的描述。本论文项目需要重新研究全球数十家博物馆的藏品，主要由私人基金会资助。这些博物馆保存了南非卡鲁组的化石，这是一个关键地区，保存了最晚二叠纪和最早三叠纪早期双孔类的巨大多样性，在这个关键时刻提供了前所未有的机会来采样化石。为该项目构建的数据集和开发的照片记录将通过NSF资助的数据库（例如，Morphobank）。

Reptiles form a critical component of the modern ecosystem, with over 20,000 known species. Fossil and molecular evidence shows that all of these living species belong to a single group, Sauria, which originated over 260 million years ago, during the Permian Period. Although saurians are rare in the Permian fossil record, they become common and diverse following a massive extinction event at the end of the Permian, 252 million years ago. This end-Permian extinction occurred at the same time as massive volcanic eruptions and acidification in oceans, wiping out an estimated 95% of species living at the time. The saurians that appear after the extinction very quickly evolve an incredible diversity of body sizes, body shapes, and diets, suggesting that they took advantage of the many gaps in the ecosystem caused by the extinction. However, the family tree of the oldest Sauria is poorly understood, and critical questions about the ancestors of all modern reptiles remain unanswered: How does the diversity of Sauria change over the period of environmental change at the end of the Permian? How rapidly did the early saurian groups change anatomically? What did the ancestor of all living reptiles look like, and how have the lineages we see today changed from that ancestor? Answering these questions will allow scientists to understand the impact that similar environmental changes occurring today, could have on living animal species. It will also provide a baseline for the changes we might expect following more serious environmental crises. Fossils from the Permian and Triassic periods are far too ancient to preserve DNA, and reconstructing their evolutionary history must rely on detailed anatomical study. Unfortunately, the anatomy of most early saurians have not been well described. This dissertation project has required restudy of dozens of museum collections worldwide, funded largely by grants from private foundations. These allowed development of the largest anatomical dataset analyzing this critical problemThese museums preserve fossils from the Karoo Formation of South Africa, a critical region that preserves a huge diversity of early diapsids from both the latest Permian and earliest Triassic,, providing an unprecedented opportunity to sample fossils at this critical moment. The dataset constructed and the photo records developed for this project will be made available to the public via NSF-funded databases (e.g., Morphobank).