Pistosaurus

Pistosaurus (exact etymology uncertain) is an extinct genus of aquatic sauropterygianreptile closely related to plesiosaurs. Fossils have been found in France and Germany, and date to the Middle Triassic. It contains a single species, Pistosaurus longaevus, which is known as the oldest "subaquatic flying" reptile on earth.

The skull of Pistosaurus generally resembles that of other Triassic sauropterygians. However, there are several synapomorphies that distinguish it from them: the long, slender snout; the possession of splint-like nasals that are excluded from the external naris; and the posterior extension of the premaxilla to the frontals. Based on synapomorphies such as the small nasals' size and the presence of interpterygoid vacuity, Pistosaurus is more closely related to the Plesiosauria than to Nothosaurus.

Pistosaurus is often mistaken with Nothosaurus and plesiosaurs. The former genus belongs to the clade Nothosauroidea also from the Triassic (approximately 251–199 million years ago), while the latter belongs to stem group Plesiosauria. Both Pistosaurus and Plesiosauria belong to the clade Pistosauroidea, which originates from the Triassic.