An extinct clade (evolutionary lineage) of eosaurop-terygian reptiles (that is, a suborder of Eosauropterygia) that also includes pachypleurosaurs (suborder Pachypleurosauria) and pistosaurs (suborder Pistosauroidea). Representatives of these groups are known from uppermost Lower Triassic to Upper Triassic marine deposits in Europe, the Near and Middle East, Northern Africa, China, and North America. Triassic nothosaurs and their relatives are typically restricted to near-shore habitats or shallow epicontinental seas. Some derived members of the pistosaurs constitute the sister group (closest relatives) to plesiosaurs, a clade that greatly diversified during the Jurassic and Cretaceous.