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PLESIOSAURUS

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Originally appearing in Volume V21, Page 837 of the 1911 Encyclopedia Britannica.
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PLESIOSAURUS , an See also:

extinct marine reptile belonging to the See also:Order Sauropterygia, which characterized the Mesozoic See also:period and had an almost See also:world-wide See also:distribution (see 'See also:REPTILES). The See also:animal is best known by nearly See also:complete skeletons from the See also:Lias of See also:England and See also:Germany. It was named Plesiosaurus (Gr. more-See also:lizard) by W. D. See also:Conybeare in 1821, to indicate that it was much more nearly a normal reptile than the See also:strange (From a memoir by See also:Professor W. Dames in the Abhandlungen der kg. preuss. Akad. d. Wiss.) Plesiosaurus guilelmi-imperatoris, restored. See also:Ichthyosaurus, which had been found in the same Liassic forma- tion a few years previously. It has a small See also:head, a See also:long and slender See also:neck, a See also:round See also:body, a very See also:short tail, and two pairs of large, elongated paddles. The snout is short, but the gape of the mouth is wide, and the jaws are provided with a See also:series of conical See also:teeth in sockets, much like those of the living gavial i Magdal6nien from the caves of Madelaine, See also:Perigord. 2 Salutr6, Bourgogne.

3 Chelles, near See also:

Paris. Other subordinate stages are the Moustbrien from Moustier, See also:Dordogne, and Acheul6en, See also:Saint Acheul. of See also:Indian See also:rivers. The neck, though long and slender, must have been rather stiff, because the bodies of the vertebrae are nearly See also:flat-ended, while they See also:bear short ribs: it could not have been See also:bent in the See also:swan-See also:fashion represented in many restorations. The other vertebrae are similarly almost flat-ended and firmly See also:united, but there is no sacrum. The ribs are single-headed, and in the See also:middle of the See also:trunk, between the supports of the paired limbs, they meet a dense plastron of abdominal ribs. The short tail is straight and rapidly tapering, but one specimen in See also:Berlin suggests that it was provided with a rhomboidal flap of skin in a See also:vertical See also:plane. The bones in the ventral See also:wall of the body which support the paired limbs are remarkably See also:expanded, and those of the See also:pectoral See also:arch have often been compared with the corresponding bones of turtles. The limbs are elongated paddles, with five complete digits, of which the constituent bones (phalanges) are unusually numerous. The only traces of skin hitherto discovered suggest that it was smooth. The reptile must have been almost exclusively aquatic, feeding on cuttlefishes, fishes and other animal See also:prey. It propelled itself chiefly by the paddles, scarcely by the tail.

The typical See also:

species is Plesiosaurus dolichodeirus, from the See also:Lower Lias of Lyme Regis, which attains a length of about three metres. Other species from the same formation seem to have measured five to six metres in length, and there are species of allied genera from the Upper Lias which are probably still larger. A See also:fine large See also:skeleton from the Upper Lias of See also:Wurttemberg, now in the Berlin Museum, is named Plesiosaurus guilelmiimperatoris (see figure above). Cryptoclidus, known by complete skeletons from the See also:Oxford See also:Clay of See also:Peterborough, differs very little from Plesiosaurus. The Cretaceous Cimoliosaurus, found in See also:North and See also:South See also:America, See also:Europe and New See also:Zealand, is also very similar. The fossilized contents of the See also:stomach in some of the later Plesiosaurs show that these reptiles swallowed stones for See also:digestive purposes like the existing crocodiles. (Monogr. Palaeont. See also:Soc., 1865) ; W. Dames, See also:paper in Abhandl. k. preuss. Akad. Wiss.

(1895), p. I. (A. S.

End of Article: PLESIOSAURUS

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PLEONASM (Gr. srAeovaoµbs, from 1rXeova?'ecv, to a... 		[next]
PLEURISY, or PLEURITIS (Gr. srXeiipc =ribs)

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