PhD: Terrestrisuchus and the origin and early evolution of crocodylomorphs

Some of the worlds most important fossils of small-bodied Late Triassic and Early Jurassic vertebrates come from the famous fissure fill deposits of southwest England and south Wales, and have provided critical insights into the origins of major groups, including dinosaurs, and the impact and response to the end-Triassic mass extinction. Among the best-preserved fossils are some of the world’s oldest and most primitive crocodylomorphs (the group including crocodilians and their immediate fossil relatives). These include the holotype and referred specimens of the small (up to 1 metre in length) crocodylomorph Terrestrisuchus gracilis, a terrestrial species with greyhound-like body proportions completely unlike those of modern crocodilians. Additional undescribed crocodylomorph specimens, some of which may represent new species, are known from a number of other localities.

The main aim of this project is to conduct a comprehensive anatomical, systematic and phylogenetic study of all of the crocodylomorph fossils from the British Mesozoic fissure fill deposits, utilising modern imaging techniques including micro-CT scanning. Key research questions include: (1) How many crocodylomorph species are present in the various fissures? Does all of the material represent Terrestrisuchus gracilis, or are additional, as-yet-undescribed, species also present? (2) Where do the fissure fill taxa within the evolutionary tree (phylogeny) of crocodylomorphs, and what does that imply about the origin and radiation of this important group, and the construction of the crocodylomorph body plan? (3) How did the British crocodylomorphs change as they matured from juveniles into adults and how quickly did they grow compared to living crocodiles? (4) How were crocodylomorphs affected by the end-Triassic extinction, how many lineages made it through, and how many lineages were lost?

The student will visit important fossil collections in the UK and the USA to examine the entirety of collected crocodylomorph fissure fill material from the Triassic-Jurassic of England and Wales. Selected specimens will be micro-CT scanned, and specialist software will be used to complete virtual 3D reconstructions of key anatomical regions (e.g. the skull). Additional visits to overseas collections (e.g. in North America, Europe, and South Africa) will allow the student to observe a wide range of comparative early crocodylomorph fossil material.

The student will build a comparative database of photos, measurements, and anatomical data for early crocodylomorphs, and will use this data to complete comprehensive anatomical descriptions, to assess the taxonomy of the fissure fill specimens, and to document patterns of ontogenetic and individual variation. These data will be used to construct a morphological character dataset for phylogenetic analysis, which will be analysed using parsimony and Bayesian approaches to elucidate the evolutionary relationships of the fissure fill material and its implications for understanding broader patterns of early crocodylomorph phylogeny. Finally, the anatomical and phylogenetic datasets will be used to quantify patterns of crocodylomorph species richness and morphological diversity (disparity) across the end-Triassic extinction event and subsequent Jurassic recovery.