Dissertation Research for Adam Pritchard: The Early Evolution and Adaptive Radiation of Saurian Reptiles

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).