Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition

ABSTRACT Marine and terrestrial animals show a mosaic of lineage extinctions and diversifications during the J urassic– C retaceous transition. However, despite its potential importance in shaping animal evolution, few palaeontological studies have focussed on this interval and the possible climate and biotic drivers of its faunal turnover. In consequence evolutionary patterns in most groups are poorly understood. We use a new, large morphological dataset to examine patterns of lineage diversity and disparity (variety of form) in the marine tetrapod clade P lesiosauria, and compare these patterns with those of other organisms. Although seven plesiosaurian lineages have been hypothesised as crossing the J urassic– C retaceous boundary, our most parsimonious topology suggests the number was only three. The robust recovery of a novel group including most C retaceous plesiosauroids ( X enopsaria, new clade) is instrumental in this result. Substantial plesiosaurian turnover occurred during the J urassic– C retaceous boundary interval, including the loss of substantial pliosaurid, and cryptoclidid diversity and disparity, followed by the radiation of X enopsaria during the E arly C retaceous. Possible physical drivers of this turnover include climatic fluctuations that influenced oceanic productivity and diversity: Late J urassic climates were characterised by widespread global monsoonal conditions and increased nutrient flux into the opening A tlantic‐ T ethys, resulting in eutrophication and a highly productive, but taxonomically depauperate, plankton. Latest J urassic and E arly C retaceous climates were more arid, resulting in oligotrophic ocean conditions and high taxonomic diversity of radiolarians, calcareous nannoplankton and possibly ammonoids. However, the observation of discordant extinction patterns in other marine tetrapod groups such as ichthyosaurs and marine crocodylomorphs suggests that clade‐specific factors may have been more important than overarching extrinsic drivers of faunal turnover during the J urassic– C retaceous boundary interval.