PLE'SIOSAU'RUS ( Nen-Lat.. from Gk.
wkijolos, ple•sios, near craiipot, sauros, lizard). A peen liarly iuter•esting fossil marine reptile of the order Sauropterygia, found in the Liassie rocks of Europe. The order Sauropterygia com prises a number of reptiles which began as small amphibians in the Trias and culminated in the Cretaceous as larger forms fully adapted to marine habits of life. They had short, thick, lizard-like bodies, very long, flexible necks, small heads. and powerful tails. The early members had elongated limbs adapted for crawling on land. which became shortened and assumed pad dle-like form in the later genera, hut which never so to fin-like organs as did those of the analogous group of ichthyosaurs (q.v.). Two families are recognized: Notho sa ridce, comprising small, more primitive forms. having five-toed feet with the normal number of finger bones or phalanges; Picsiosaaridm. com prising large animals with paddle-shaped limbs and the digits lengthened by an increased numher of phalanges, and with the pectoral girdle enlarged to form a protective covering for the thorax. Lariosaurns and Nothosaurus from the' Triassic of Europe are the important genera of the first family; and Plesiosaurus from the Massie of Europe and Cimoliosaurus from the Cretaceous of America and New Zealand are representative of the second family.
The genus Nothosa urns, %%hid' attained a length of about ten feet, had a long flattened skull and small eyes near the I riddle of the head. The teeth were numerous. small and regular in the posterior portion of the jaws, but large and "yenned, like spreading tusks, in the front. I'll.siosuarus had a proportiOnately smaller head of triangular form and a neck which in sonic species (-weeded in length the remainder of the body. and which was supported in the different speeies by from 23 to 40 cervical vertebra.. The teeth arc not sn numerous as in NothoAlurtis. and :ire larger. reeurved, and interlocking. The
pelt ie and pectoral limbs are remarkably similar to each other in form, and the phalanges of both were imbedded in cartilage which filled out the form of the paddle just as in the ichthyosaurs, These creatures varied from 10 to 20 feet in length, and they must have been very abundant in the Liassie seas of England and Germany, where finely preserved skeletons of them have been obtained. Twenty-five species are known in the Lias of England alone. Pliosaurus is a gigantic plesiosaur with a skull nearly five feet long and teeth twelve inches long. found in the English Upper .1nrassie, and it is possibly a synthetic type between the ichthyosaurs and the American representatives of the plesiosaurs have been found in the Upper Jurassic beds of Alabama. New Jersey, Kansas, aml Wyoming. and have been described under the names Chnoliosanrus. ,Ilegalosaurus. Elasmo sa urns. Iolieborhync•hops, etc. A skeleton of Cope's Elasmosauras from the Upper Cretaceous of Fort Wallace. Kansas, lacking the head. meas ures 42 feet, in length, of which the neck, with 72 vertebra., occupies 22 feet. Some of the Amu•ric:nn examples have afforded interesting evidence of the feeding habits of these creatures. Mimes of various sizes from one-quarter inch to four inches diameter were found in the position of the stomach. and are supposed to have been swallowed by the animals as aids to digestion. One specimen had 125 such stones in its stomach. Plesiosaurs, as ellVier expressed it, combine the paddle'. of a whale. the head of a lizard, and a long neck like the body of a serpent. They were powerful animals. swimming freely about the shallow seas of Jurassie and Cretaceous times, and feeding upon the fish and smaller marine reptiles, for preying upon which their long necks and numerous spreading teeth admirably fitted t hen].