Cretaceous plesiosaurs ate ammonites

摘要

The Plesiosauria, large Mesozoic marine reptiles, have been regarded as dominant predators in Mesozoic seas, although there is only a little (including some doubtful) direct evidence of their stomach contents. Here we report the occurrence in Hokkaido, northern Japan, of a partial skeleton of a Cretaceous short-necked plesiosaur together with a large number of isolated ammonoid jaws . This is, to our knowledge, the first description of the stomach contents of a polycotylid plesiosaur, and the first firm evidence of prey-predator relationships between plesiosaurs and ammonites.