Nothosaurus ('false lizard', from the Ancient Greek νόθος, nothos, 'illegitimate' and σαῦρος, sauros, 'lizard') is an extinct genus of sauropterygian reptile from the Triassic period, approximately 240–210 million years ago, with fossils being distributed throughout the former Tethys Ocean, from North Africa and Europe to China.

The skull was broad and flat, with long jaws, lined with needle teeth, it probably caught fish and other marine creatures.

[17] Recently, the long considered lost type material of N. schimperi Meyer, 1842 from the Lower Muschelkalk of Soultz-les-Bains, Alsace, France, has been rediscovered and a lectotype has been designated.

[17] N. edingerae N. giganteus N. mirabilis N. haasi N. tchernovi N. jagisteus N. marchicus N. winterswijkensis N. youngi N. yangiuanensis N. juvenilis N. winkelhorsti Several other species have been named but are now generally considered invalid.

[19][20] Other species now considered junior synonyms of N. marchicus include N. crassus, N. oldenburgi, N. raabi, N. schroderi, N. venustus and the recently named N. winterswijkensis.