Plesiopleurodon is a genus of marine reptile, known as pliosaurs. The genus of Plesiopleurodon contains only one species, which is Plesiopleurodon wellesi. This means that it is the type species. The only specimen was discovered in the Rattlesnake Hills of Wyoming by the American Paleontologist, Kenneth Carpenter. Plesiopleurodon is a relatively small variety of pliosaur, reaching less than 3 meters. It lived during the Late Cretaceous Period and fed mostly on fish and other small sea creatures.