Sauropterygia

Sauropterygians Temporal range: Early Triassic - Late Cretaceous, 247–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Sauropterygia diversity. Clockwise from top left: Ceresiosaurus calcagnii (Nothosauroidea), Henodus chelyops (Placodontia), Brachauchenius lucasi, Aristonectes parvidens (Plesiosauria).
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Neodiapsida
Superorder:	†Sauropterygia Owen, 1860
Subgroups
†Atopodentatus †Hanosaurus †Helveticosauridae? †Placodontiformes †Saurosphargidae †Eosauropterygia †Nothosauria †Pachypleurosauria †Pistosauroidea †Plesiosauria

Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic diapsid reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became extinct at the end of that period. The plesiosaurs would continue to diversify until the end of the Mesozoic, when they became extinct as part of the end-Cretaceous mass extinction. Sauropterygians are united by a radical adaptation of their pectoral girdle, adapted to support powerful flipper strokes. Some later sauropterygians, such as the pliosaurs, developed a similar mechanism in their pelvis. Other than being diapsids, their affinities to other reptiles have long been contentious. Sometimes suggested to be closely related to turtles, other proposals have considered them most closely related to Lepidosauromorpha or Archosauromorpha, and/or the marine reptile groups Thalattosauria and Ichthyosauromorpha.