98 



WATER REPTILES OF THE PAST AND PRESENT 



V^V 



J 



The Nothosauria were much smaller reptiles than the plesio- 

 saurs, none of them perhaps exceeding the size of the smallest known 

 plesiosaurs. They were semiaquatic in habit, with many curious 



resemblances to otht r 

 semiaquatic reptiles of 

 a later time known, as 

 the dolichosaurs. The 

 neck is more or less 

 elongated, having about 

 twenty vertebrae in the 

 longest-necked forms; 

 the body is moderately 

 long, and broad, and 

 the tail is relatively 

 ^ shfixt^ The vertebrae 

 and ribs are quite like 

 those of the plesiosaurs, 

 that is, the yextjebrae 



Fig. 46. — Pectoral girdle of Xolhosaurus, from 

 photograph by E. Fraas: /(7, interclavicle; cl, 

 clavicle; sc, scapula; cor, coracoid. 



are gently concave at 

 each end, and the dorsal ribs are attached by a single head to ihe^ 

 transverse process high up on the arch ; the cervical ribs are double- 

 headed, precisely like those of the older plesiosaurs, one of the char- 

 acters which insistently proves 

 the relationships of the two 

 groups. The bones of the shoul- 

 ders (Fig. 46) also have many 

 resemblances to the extraor- 

 dinary ones of the plesiosaurs, 

 though they are much less 

 specialized. There was no 

 sternum; the coracoids are 

 large, though very much 

 smaller than those of the plesi- 

 osaurs. The collar-bones are large and strong, joining each other 

 in front of the coracoids and firmh- united with the shoulder- 

 blades at the outer extremity. Four vertebrae are united to form 

 a sacrum, and their union with the hip bones (Fig. 47) was much 



Fig. 47. — Pelvic bones of Xolhosaiint.':: 

 il. ilium; or, acetabulum; p, pubis; /.r, 

 ischium, (.\ftcr Andrews.) 



