Pliosauroidea is an extinct clade (group) of marine reptiles. Pliosauroids, also commonly known as pliosaurs, are known from the Jurassic and Cretaceous Periods. The pliosauroids were short-necked plesiosaurs with large heads and massive toothed jaws. These swimming reptiles were not dinosaurs, but distant cousins of modern lizards.

The distinguishing characteristics are a short neck and an elongated head, with larger hind flippers compared to the fore flippers, vice-versa of the plesiosaurs. They were carnivorous and their long and powerful jaws carried many sharp, conical teeth. Pliosaurs range from 13 to 49 feet (4 to 15 metres) and more in length. Their prey may have included fish, sharks, ichthyosaurs, dinosaurs and other plesiosaurs.