Plesiosaur is a collective term for the extinct marine reptiles of the genus Plesiosaur, belonging to the suborder Diptera and the order Pterosauriformes. It is a group adapted to living in shallow water environments, with large individuals and long necks, hence its name. It began to appear in the late Triassic period and spread all over the world by the Jurassic period, and became extinct by the end of the Cretaceous period. The plesiosaur were incredibly large in size and ruled the oceans of the Mesozoic era alongside ichthyosaurs. Its living habits are similar to modern sea lions, mainly living in the ocean and feeding on fish. It can be divided into long necked plesiosaurs and short necked plesiosaurs. Survived from Jurassic to Cretaceous.