Exploring the correlation between plesiosaur occurrences and continental flooding events

Abstract

Plesiosaurs (Sauropterygia, Plesiosauria) were a prominent group of Mesozoic marine reptiles with a rich and widespread fossil record dispersed across all continents. However, their diversity patterns and the nature of their fossil record remain poorly understood in relation to environmental and geological factors. This study explores the correlation between the continental flooding area (COFA) and plesiosaur occurrences, integrating taxic and phylogenetic diversity estimates (TDE and PDE) and morphological disparity analyses. Additionally, the study extends the analysis to other marine reptile groups, including Mosasauridae, Ichthyosauria, and Thalattosuchia, to compare differences in their responses to environmental changes. The results reveal a significant positive correlation between plesiosaur occurrences and COFA values, suggesting a strong link between the expansion of shallow epicontinental seas and the plesiosaur fossil record. Among the marine reptile groups analyzed, this relationship is observed only in plesiosaurs. Moreover, taxic diversity estimates (TDE) correlate positively with plesiosaur occurrences but not with fossiliferous marine formations (FMF), indicating that sampling biases alone do not fully explain diversity trends. Finally, morphological disparity patterns suggest that the marked increase in plesiosaur occurrences during the Late Cretaceous was not accompanied by a rise in disparity. These findings provide new insights into the paleoecology of Mesozoic marine reptiles and their responses to environmental changes, suggesting that plesiosaurs may have responded differently to episodes of continental flooding, potentially through a greater use of shallow and marginal marine environments (estuaries) compared with the other marine reptile groups analyzed.