Liopleurodon

Liopleurodon (; meaning 'smooth-sided teeth') is an extinct genus of carnivorous pliosaurid plesiosaurs that lived from the Callovian stage of the Middle Jurassic to the Kimmeridgian stage of the Late Jurassic period (approximately 166 to 155 million years ago). The type species is L. ferox, which is probably the only valid species. Some studies also include the second species L. pachydeirus, but this latter is considered as a probable junior synonym of L. ferox due to its lack of viable diagnosis. Fossils attributed to Liopleurodon, including some skeletons, are mainly known from Europe, with one occurrence reported in Mexico. As the holotype specimen of L. ferox consists of a single tooth preserving questionable distinctive features, recent studies therefore recommend the necessary identification of a neotype in order to preserve its validity. Other additional species were even proposed, but these are currently seen as coming from other pliosaurid genera.

Like other plesiosaurs, Liopleurodon has four flippers, a short tail, and, like most pliosaurids, a long head and a short neck. In 1999, its size was greatly exaggerated in the BBC documentary series Walking with Dinosaurs, where it was depicted as reaching in length. However, the different attributed specimens show that the animal could reach a size ranging from long, with some researchers estimating a maximum length of approximately . Various studies show that Liopleurodon would have been an ambush predator, feeding on fish, cephalopods and other marine reptiles.