NEW DATA ON THE POSTCRANIAL ANATOMY OF THE CALIFORNIA MOSASAUR PLOTOSAURUS BENNISONI (CAMP, 1942) (UPPER CRETACEOUS: MAASTRICHTIAN), AND THE TAXONOMIC STATUS OF P. TUCKERI (CAMP, 1942)

New axial and appendicular material permits a detailed re-description of the postcranial skeleton of the derived mid-Maastrichtian California mosasaur genus Plotosaurus. Centrum morphology, vertebral process shape, and extreme hyperphalangy provide compelling evidence to demonstrate that Plotosaurus achieved the highest level of aquatic adaptation among mosasaurs. A re-examination of the type material of P. bennisoni and of P. tuckeri indicates that only one taxon, P. bennisoni, is present, of which P. tuckeri is a junior synonym.