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an order of extinct aquatic predatory reptiles of the subclass Synaptosauria. The Triassic notosaurs had a body structure typical of terrestrial animals; the later (Jurassic-Cretaceous) plesiosaurs were similar in appearance and way of life to seals and other pinniped mammals, and they almost lost connection with dry land. Some Sauropterygia, especially the later ones, were characterized by a very long and flexible neck (elasmosaurs) with an increased number of vertebrae.
There were approximately 15 families (comprising several dozen genera). Numerous remains of Sauropterygia have been found on all the continents, including the territory of the USSR. Sauropterygia are interesting as an elucidation of the history of reptiles and their adaptation to an aquatic environment.