Pliosauroidea

Pliosauroidea is an extinctclade of plesiosaurs, known from the latest Triassic to early Late Cretaceous. They are best known for the subclade Thalassophonea, which contained crocodile-like short-necked forms with large heads and massive toothed jaws, commonly known as pliosaurs. More primitive non-thalassophonean pliosauroids resembled plesiosaurs in possessing relatively long necks and smaller heads. They originally included only members of the family Pliosauridae, of the order Plesiosauria, but several other genera and families are now also included, the number and details of which vary according to the classification used.

The distinguishing characteristics are a short neck and an elongated head, with larger hind flippers compared to the fore flippers, the opposite of the plesiosaurs. They were carnivorous and their long and powerful jaws carried many sharp, conical teeth. Pliosaurs range from 4 to 10 meters or more in length. Their prey may have included fish and, in the more macropredatory taxa, sharks, ichthyosaurs, other plesiosaurs, and possibly dinosaurs.

The largest known taxa, all reaching lengths of around 10m, include Kronosaurus, Sachicasaurus, Monquirasaurus, and Pliosaurus; other well-known genera include Rhomaleosaurus, Peloneustes, Liopleurodon, and Macroplata. Fossil specimens have been found in Africa, Australia, China, Europe, North America and South America.

Many very early (from the Early Jurassic and possibly Latest Triassic, i.e. Rhaetian) primitive pliosauroids were very like plesiosauroids in appearance and, indeed, used to be included in the family Plesiosauridae.