Understanding the diversification dynamics of the Permo?Triassic archosauromorph radiation using occurrence-based Bayesian approaches

112. SOOKIAS R.B., PRADELLI L., ASCARRUNZ E., SILVESTRO D., EZCURRA M.D.

Congreso; The Palaeontological Association 65th Annual Meeting; 2021

The archosauromorph radiation started during the Triassic and was one of the mostspectacular adaptive radiations in Earth history, giving rise to diverse stem and crownarchosaur taxa, dominating the Mesozoic land and skies for >150 Ma; it provides anoutstanding opportunity to test hypotheses regarding the process of adaptive radiation.Given a patchy fossil record, distant extant relatives and long ghost lineages, methodsbased on phylogenetic topologies are subject to a high degree of inference. We thus employthe Bayesian occurrence-based approach PyRate to better understand the diversificationdynamics of archosauromorphs, using a dataset of first and last occurrences and body sizeproxy data from the Late Permian?Early Jurassic. Using a fossilized birth death model, wefind evidence for a peak in net diversification in the latest Permian, indicating initial radiationdirectly concurrent with extinctions. This flatlines in the Late Triassic, indicating slowdownfollowing niche-filling. Pseudosuchians peaked in diversification in the Ladinian and Carnianbut suffered major Late Triassic extinction parallel to saurischian expansion. These resultsindicate a niche-related ?early burst? of diversification, initially potentially morphologicallycryptic. We also find a negative correlation between body size and extinction (positive withlongevity), indicating rapid evolutionary turnover among smaller‑bodied taxa.