Analysing Thalattosuchia paleobiodiversity under the prism of phylogenetic comparative methods

Thalattosuchia is a particularly diverse group of mostly marine crocodylomorphs that lived during most of the Jurassic and Lower Cretaceous. Previous studies have sought to uncover the factors influencing Crocodylomorph evolution, yielding mixed results, possibly due to Thalattosuchia’s unique ecological niche and controversial phylogenetic placement among Crocodylomorph. Here, we propose a Thalattosuchia-focused study using phylogenetically-informed statistical analyses. First, we tested the phylogenetic structure of thalattosuchian survival at various geological transitions. We then tested the influence of biotic and abiotic factors on thalattosuchian diversity at the aforementioned crises. Finally, we tested whether diet was an additional explanatory factor. We found that (1) thalattosuchian diversification at the Lower-Middle Jurassic transition was phylogenetically structured and associated with signs of snout reduction possibly explained by the colonisation of emptied ecological niches, allowing the emergence of Machimosaurinae and Geosaurinae ; (2) we observed higher local temperatures for Thalattosuchia after the Middle-Upper Jurassic and Jurassic-Cretaceous transitions, the former being in accordance with most climatic literature and the latter being subject to more caution; Finally, (3) we corroborated previous studies about skull shape and found that durophageous teleosauroids tended to have larger body sizes than any other diet, possibly as a result of ecological specialization. We also found evidences of niche partitioning among piscivorous and macrophageous metriorhynchoids that is observable by a size range extension.