Enigmatic large-toothed Campanian polycotylid plesiosaurs with specific dietary preferences and potentially wide distribution

Most polycotylid plesiosaurians have isodont dentition with relatively small and slender conical teeth. However, large and robust caniniform teeth are known for some of their basal late Albian and early Cenomanian representatives, implying greater ecological diversity early in the evolutionary history of the clade. Here we report the first evidence of polycotylids with large teeth in the Campanian, thus c. 15 Myr younger than previous records. Several teeth with crowns exceeding 40 mm in height and some reaching 25 mm in basal diameter were collected from two Campanian localities in European Russia. These are the largest polycotylid teeth reported from the Cretaceous of Eurasia. Their large size and specific enamel ornamentation markedly differ from other known polycotylid teeth, suggesting that these teeth belong to an undescribed taxon. However, similar enamel ornamentation was previously reported for the now forgotten ‘Piratosaurus plicatus’ Leidy, 1865 from the Upper Cretaceous of Canada, which may indicate the wide distribution of polycotylids with such teeth in the latest Cretaceous. Unlike classical polycotylids, the new teeth have strong apical wear which implies consumption of abrasive prey, similar to modern killer whales that feed on sharks. Thus, our finding reveals higher ecological diversity of polycotylids in the latest Cretaceous, suggesting the coexistence of small-to medium-toothed and large-toothed (probably ‘latirostrine’) taxa at different times of the evolutionary history of the Polycotylidae.