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2万种。化石和分子证据表明，所有这些现存物种都属于一个单一的类群——蜥蜴，它们起源于2.6亿年前的二叠纪时期。尽管在二叠纪的化石记录中，蜥蜴很少见，但在2.52亿年前二叠纪末期的一次大规模灭绝事件之后，它们变得普遍而多样。二叠纪末的大灭绝与大规模火山爆发和海洋酸化同时发生，估计当时95%的物种灭绝。大灭绝后出现的蜥蜴在体型、体型和饮食上迅速进化出了令人难以置信的多样性，这表明它们利用了大灭绝造成的生态系统中的许多空白。然而，人们对最古老的蜥蜴的家谱知之甚少，关于所有现代爬行动物祖先的关键问题仍未得到解答：在二叠纪末期的环境变化中，蜥蜴的多样性是如何变化的？早期的蜥蜴种群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，我们今天看到的谱系与那个祖先有什么不同？回答这些问题将使科学家们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，无法保存DNA，重建它们的进化史必须依赖于详细的解剖研究。不幸的是，大多数早期蜥蜴的解剖结构并没有得到很好的描述。这个论文项目需要重新研究世界上几十个博物馆的藏品，主要由私人基金会资助。这些博物馆保存了来自南非卡鲁地层的化石，这是一个保存了大量来自二叠纪晚期和三叠纪早期的早期潜虫的关键地区，为在这个关键时刻取样化石提供了前所未有的机会。为此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（如Morphobank）向公众开放。

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).