Abstract The largest diversity of Jurassic marine reptiles from Gondwana has been recorded in the Neuquén Basin. Although the Early Jurassic records are limited, the records from the Middle Jurassic, especially the early Bajocian plesiosaurs and ichthyosaurs, are unique in the world. The highest abundance and taxonomic diversity is recorded from the Late Jurassic (Tithonian). Pleurodiran ( Notoemys ) and cryptodiran turtles ( Neusticemys ), ichthyosaurs ( Ophthalmosaurus, Caypullisaurus ), pliosaurs ( Pliosaurus, Liopleurodon ) and crocodilians ( Geosaurus, Metriorhynchus, Dakosaurus ) are members of this rich marine herpetofauna. Except for Notoemys, the other reptiles are pelagic. Their habits and large size ( Caypullisaurus, Liopleurodon, Dakosaurus ) suggest that they entered the sheltered Neuquén Basin occasionally, possibly for reproduction in protected areas. The model of a protected basin, open to the Pacific Ocean through gaps in an emergent by island-arc complex, fits well with the ecological requirements inferred for most of the pelagic reptiles. The Caribbean Corridor may also have played a significant role as a seaway at least during the Middle Jurassic and probably before. New findings in Tithonian and Berriasian sediments of the Neuquén Basin suggest that there was no massive extinction among the marine herpetofauna at the Jurassic–Cretaceous boundary.