Plotosaurus

Plotosaurus; Temporal range: Maastrichtian, ; ~Possible late Campanian record.
	Mounted skeleton (CIT 2750) at the Natural History Museum of Los Angeles County
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Clade:	†Mosasauria
Family:	†Mosasauridae
Genus:	†Plotosaurus; Camp, 1951
Species:	†P. bennisoni
Binomial name
	†Plotosaurus bennisoni; (Camp, 1942)
Synonyms
	List of synonyms Synonyms of genus Kolposaurus Camp, 1942 (preoccupied); Garzasaurus Anderson, 1943; ; Synonyms of P. bennisoni Kolposaurus tuckeri Camp, 1942; Plotosaurus tuckeri (Camp, 1942); ; ;

Plotosaurus ("swimmer lizard") is an extinct genus of large mosasaurs which lived during the Upper Cretaceous (Maastrichtian) in what is now North America. The taxon was initially described by Berkeley paleontologist Charles Lewis Camp in 1942 from several more or less complete fossil specimens discovered in California, USA. Originally named as 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. Two species were historically assigned to the genus, but since 2008, only P. bennisoni has been recognized as valid.

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. It is these same adaptations that have led to its classification in a rather derived position within this group of marine reptiles. Although only known from North America, fragmentary specimens known from Japan that could possibly belong to the genus suggest that it may have had a wider distribution.