| Named By: | Richard Owen in 1841 |
| Time Period: | Late Jurassic, 155.7-147 Ma |
| Location: | England - Kimmeridge Clay Formation, and Norway, Svalbard, Spitsbergen. Possibly also France, Poland and Russia, depending upon the validity of all species |
| Size: | Some species up to 10 meters long, with skulls approximately 2 meters long. Largest species, P. funkei estimated at between 10-12.8 meters long |
| Diet: | Carnivore |
| Fossil(s): | Numerous specimens |
| Classification: | | Chordata | Reptilia | Sauropterygia | Plesiosauria | Pliosauridae | |
| Also known as: | | Liopleurodon rossicus | Plesiosaurus giganteus | Plesiosaurus recentior | Spondylosaurus | Stretosaurus | Strongylokroptaphus | |
Pliosaurus (meaning 'more lizard') is an extinct genus of thalassophonean pliosaurid known from the Kimmeridgian and Tithonian stages (Late Jurassic) of Europe and South America. Their diet would have included fish, cephalopods, and marine reptiles. This genus has contained many species in the past but recent reviews found only six to be valid, while the validity of two additional species awaits a petition to the ICZN. Pliosaurus currently consists of the type species P. brachydeirus, and also P. brachyspondylus, P. carpenteri, P. funkei, P. kevani, P. macromerus, P. rossicus and P. westburyensis, as well as the invalid P. portentificus. Most species of Pliosaurus are notable for their large body size, while the others, P. brachydeirus, P. brachyspondylus and P. portentificus, are known exclusively from immature individuals. Species of this genus are differentiated from other pliosaurids based on seven autapomorphies, including teeth that are triangular in cross section.