Plotosaurus
Plotosaurus ("swimmer lizard") is an extinct genus of mosasaurs who lived during the Upper Cretaceous (Maastrichtian) in what is now North America. Only one species is recognized, P. bennisoni, described by Berkeley paleontologist Charles Lewis Camp in 1942 from fossils discovered in California. Originally named Kolposaurus (meaning "bay lizard"), it was changed to Plotosaurus in 1951 when Camp discovered that the name had already been assigned to a type of nothosaur. Unlike other mosasaurids, Plotosaurus possesses a morphology converging with those of ichthyosaurs, suggesting a much more advanced swimming adaptation than some of its close relatives. Discovery and naming The earliest described specimens of Plotosaurus were discovered in the early 20th century from Moreno Formation deposits along the San Joaquin Valley, California. The first was a pair of caudal vertebrae collected during 1918 or 1920 by an Oakland resident named Herman G. Walker while exploring the Panoche Hills. They were donated to the University of California, Berkeley's Museum of Paleontology under the catalog UCMP 36050. In June 1936, a high school student from Gustine named Allan Bennison found three vertebrae next to a hadrosaur fossil in shale hills near Patterson, two of which he donated to UC Berkeley as UCMP