458 LOWER VERTEBRATES. 



the scapular and pelvic arches, as well as several bones of the limbs, being remarkably 

 like those portions in the Monotrema, especially Echidna. From a comparative study 

 of the Pelicosauria, the fact has been demonstrated that the first terrestrial Vertebrata 

 possessed a notochord. The Dicynodons are known from fragments of their skeletons 

 found f ossilled in South Africa, and received their name from the Greek, ' two-tusks.' 

 The skull presents characters which are crocodilian, chelonian, lacertilian, and, in the 

 elongate canine teeth, mammalian. The lower jaw was remarkably turtle-like and was 

 probably encased in horn. Several species have been described. The Oudenodons 

 were without teeth or had them inconsjiiicuous. The head was rounded anteriorly, 

 and in general outline strongly resembled that of the turtles. The Pelicosauria are 

 represented by two dozen or more species from the pei'mian beds of America; Clepsy- 

 dropus, from Texas and Illinois, is illustrative. 



Order VIII. — SAUROPTERYGIA. 



The European and New Zealand cretaceous beds have yielded by far the greater 

 number of species to this order. Of the few American forms, Elasmosaurus is the 

 most interesting. This animal differed from the Plesiosaurus in the structure of its 



pectoral girdle, and was of an elongated 

 form, sometimes forty-five feet in length, 

 and could swim rapidly through the water by 

 using its flattened limbs as oars, or by pro- 

 pelling itself, the tail being long and paddle- 

 shaped. The neck and small head resembled 

 in their motions, as they twisted from side 

 to side or plunged beneath the surface these 

 portions of the swan. It has been found, 

 FIG. 264. - Skull of Dicynodm.. ^ ™"i '™ examination of the debris occupying 



what was once the body cavity of these 

 sea-saurians, that they fed on the more ravenous fish, which they were enabled to 

 grasp and retain by means of their long, sharp teeth. 



While the Mlasmosaurs ploughed the American waters, the Plesiosauri were no less 

 abundant in the eastern hemisphere. The first fossil representative was found in the 

 lias of Lyme Regis, and, from its peculiar lizard-like form, derived its naine, ' near to 

 lizard.' The discovery of this genus was considered by Cuvier to be of great im- 

 portance, as presenting peculiarities of structure the most anomalous. Perhaps the 

 better way to describe the animal is to follow the words of an early naturalist : 

 " To the head of a lizard it united the teeth of a crocodile, a neck of enormous length, 

 resembling the body of a serpent, a trunk and tail having the proportions of an ordi- 

 nary quadruped, the ribs of a chameleon, and the paddles of a whale." The openings 

 of the nostrils were far back, in front of the eyes, and may have been used as spout- 

 holes. Of a score or more of species which have been described, P. dolichodeirus, 

 which attained a length of twelve feet, is, j)erhaps, the most commonly found. The 

 neck was of great length, exceeding, by several vertebrae, that of the swan. A study 

 of the ribs shows the animal to have been capable of taking in a large supply of air, 

 and the inference is that it could remain submerged for a considerable period of time. 

 It was, moreover, less adapted for a pelagic life than the Ichthyosaurus and probably 

 seldom wandered far from the more shallow waters. 



