274 TOWARDS THE HUMAN FORM 



details of their shoulder-girdle, whose scapulas were joined 

 ventrally instead of remaining separate as in Plesiosaurians. 

 Elasmosaiirus of the Upper Cretaceous of Kansas had a neck 

 about seven metres long, to a total length of fifteen metres. 

 Pliosaurus, which was ten metres long and whose bones are 

 found in the Kimmeridge clay, probably swam under water 

 more habitually than the other species. Its cervical vertebrae, 

 twenty in number, were, in fact, flattened as if they had been 

 compressed by the resistance of the water. They were 

 creatures of terrible aspect, armed with formidable teeth, some 

 of which were three decimetres in length, and would not have 

 found on the coasts prey worthy of such a powerful maxillary 

 apparatus. The limbs of all these Plesiosaurians w y ere less 

 modified than those of the Ichthyosaurians. They never had 

 more than five digits, whereas the Ichthyosaurians sometimes 

 had six owing to the division of one of them. The number of 

 phalanges only was notably augmented. The humerus, radius, 

 and ulna, as well as the corresponding bones of the hind- 

 limb, remained considerably more elongated than the 

 carpus, tarsus, and digits. 



While the Ichthyosaurians and Plesiosaurians, which had 

 sprung from the lower forms of Reptiles, disappeared from the 

 seas of the Upper Cretaceous, other Saurians became aquatic 

 and even marine ; but they were quite differently characterized. 

 They seem at first to have appeared in the southern seas. Their 

 dentition clearly indicates their relationship with the Lacer- 

 tilians. The Plesiosaurians had each tooth implanted in an 

 alveolus, while those of the Ichthyosauri an were aligned in 

 grooves, not divided into alveoli. Those of the new aquatic 

 Reptiles, the Pythonomorphs, were simply welded to the 

 maxillaries as in numerous Lacertilians. But the form of these 

 teeth was varied, and this gave the palaeontologist Dollo some 

 indications as to the nature of their food. The powerful dentition 

 of Mosasauras indicates that they doubtless attacked either 

 less well-armed Mosasaurians or marine Chelonians. The thin 

 curved teeth and weak jaws of Plioplatecarpiis would hardly 

 have allowed it to attack any but medium-sized molluscs 

 such as the Belemnitellae. Globidens with its rounded teeth 

 and weak jaws probably fed on sea-urchins. This is no 

 mere hypothesis ; their prey has sometimes been found 

 fossilized along with them. 1 These animals already existed 



1 XCIV. 



