Pistosaurus longaevus is an extinct genus of aquatic sauropterygian reptile belonging to the plesiosaur order. It was about 3 m (10 ft) long.

Previously Pistosaurus was classified as an advanced nothosaur, the presumed ancestors of plesiosaurs, but it has since been reclassified as a primitive plesiosaur. This makes it the oldest plesiosaur known, and the only one from the Triassic period. Pistosaurus shows physical traits of both nothosaurs (pallet and body shape) and plesiosaurs (stiff vertebral column). Its flippers and long neck also resembled a plesiosaur's.

Sauropterygia

Pistosaurus