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the most extensive suborder of large fossil reptiles of the order Sauropterygia of the subclass Synaptosauria. The Plesiosauria lived during the Triassic through Cretaceous periods. The body measured up to 15 m long and had 100–150 vertebrae, with flat articulated surfaces. The extremities were highly developed and flipper-like, with an increased number of phalanges. The nostrils were displaced toward the orbits; a middie longitudinal pectén, characteristic of many predators, was sharply expressed at the posterior part of the skull. The teeth were conical and either homogeneous or differentiated into highly developed fangs and smaller teeth. The Plesiosauria were predators. They inhabited primarily littoral zones and fed principally on fish. Two types are differentiated: Plesiosauria with long necks and small heads, such as the Plesiosaurus and Elas-mosaurus, and those with short necks and large heads, such as the Pliosaurus. The Plesiosauria probably descended from the Nothosauria. Their remains have been discovered on all continents and are especially numerous in Jurassic deposits in Europe. In the USSR they have been found in such areas as the Middle Volga Region, the Trans-Volga Region, northwestern Kazakhstan, and Iakutia.
REFERENCEOsnovy paleontologa: Zemnovodnye, presmykaiushchiesia i ptitsy. Moscow, 1964.
A. K. ROZHDESTVENSKII