Plesiopleurodon

Plesiopleurodon (/ˌpliːsiəˈplʊərədɒn/; Greek: plesios, meaning “near to”, pleuro, meaning “side”, and don, meaning “tooth”) is an extinct genus of Mesozoic marine reptiles, belonging to Sauropterygia, known from the Late Cretaceous of North America. It was named by Kenneth Carpenter based on a complete skull with a mandible, cervical vertebra, and a coracoid. In naming the specimen, Carpenter noted "Of all known pliosaurs, Plesiopleurodon wellesi most closely resembles Liopleurodon ferox from the Oxfordian of Europe, hence the generic reference." It was initially described as a pliosaur due to it short neck, a common trait of the family, although it is in the order Plesiosauria. However, later exploration into the relationships of both orders indicate that not all pliosaurs have short necks and not all plesiosaurs have long necks.

It is distinguishable by its short neck, elongated head, and comparatively few teeth in the symphysis when compared to other plesiosaurs.