SAUROPTERYGIAN

any of the extinct reptiles of the order Sauropterygia, animals remarkably well-adapted to an aquatic life and including the nothosaurs, the plesiosaurs, and possibly the placodonts, all of Mesozoic age (66.4 to 245 million years old). The largest of these creatures were certain plesiosaurs that attained a length of 12 m (40 feet). The characteristics of the sauropterygians are associated with a mode of swimming accomplished by rowing motions of powerful limbs, contrasting with the more fishlike mode of locomotion in ichthyosaurs and mosasaurs. The most primitive sauropterygians were the nothosaurs of the Triassic Period (245 to 208 million years ago). In these small reptiles the body was long and slender; the limbs were comparable to those in terrestrial reptiles, suggesting some degree of mobility on land. The nothosaurs are structurally antecedent to plesiosaurs. See also Nothosaurus. Plesiosaurs appeared at the end of the Triassic and remained prominent until the Late Cretaceous Epoch (97.5 to 66.4 million years ago); specimens are most common in the Jurassic strata (208 to 144 million years ago) of England and Germany and the Late Cretaceous of the United States. The tail was short, while the neck was elongated in most species. The trunk was broad and stout, with the ventral parts of shoulder and pelvic girdles greatly expanded for the attachment of powerful limb muscles. The limbs were long, narrow flippers that had numerous finger (or toe) joints for increased flexibility. The long jaws contained pointed teeth appropriate for seizing fish. See also plesiosaur. Often considered as a suborder of the Sauropterygia are the placodonts of the Middle Triassic. The body was structurally similar to that of nothosaurs but more compact. In Placodus and other typical forms, there were broad, flat tooth plates for crushing the mollusks on which they fed. Many placodonts developed dermal armour; Henodus had a shell comparable to that of a turtle.