Refining the marine reptile turnover at the Early–Middle Jurassic transition

Even though a handful of long-lived reptilian clades dominated Mesozoic marine ecosystems, several biotic turnovers drastically changed the taxonomic composition these communities. A seemingly slow paced, within-geological period turnover took place across Early–Middle Jurassic transition. This saw demise early neoichthyosaurians, rhomaleosaurid plesiosaurians and plesiosauroids in favour ophthalmosaurid ichthyosaurians cryptoclidid pliosaurid plesiosaurians, that will dominate Late and, for two them, entire Early Cretaceous as well. The fossil record this is however extremely poor change dominance appears to be spread middle Toarcian–Bathonian interval. We describe series ichthyosaurian plesiosaurian specimens from successive geological formations Luxembourg Belgium detail evolution reptile assemblages transition within single area, Belgo–Luxembourgian sub-basin. These fossils reveal continuing large microcleidid Temnodontosaurus -like up latest Toarcian, indicating structuration upper tier Western Europe ecosystems remained essentially constant very end Jurassic. also suddenly by Bajocian. results geographically-restricted area provide clearer picture shape occurring at early–Middle event restricted sole Aalenian stage, reducing uncertainty its duration, least 4 instead 14 million years.