PLESIOSAURS. 



103 



from the Cretaceous strata having a neck much exceeding the body and tail in 

 length, and containing as many as forty vertebrse. Marine and carnivorous in 

 their habits, these formidable creatures probably lurked in shoal-water, from 

 whence they darted their long necks to seize passing fishes in their jaws. 

 In the groups mentioned the head was comparatively small, but in the huge 

 pliosaurs (Pliosaurus) of the upper Oolitic strata the skull was of enormous 

 size, attaining in some instances a length of 6 feet, and the neck proportionately 

 short and thick. Their 

 teeth had more or less 

 triangular crowns, and 

 in some cases, inclusive 

 of the root, measured 

 quite a foot in length. 

 As is the case 

 with all the higher 

 aquatic Vertebrates, 

 there is evidence to 

 show that the plesio- 

 saurs were originally 

 derived from land 

 animals ; the repre- 

 sentatives of the 

 group found in the 

 earlier (Triassic) 

 Secondary rocks hav- 

 ing limbs departing 

 much less widely from pr . Z} and^.z, anterior and posterior articular surfaces of the arch ; co, rib. 



the ordinary type, 



and bearing claws at the extremities of their digits. In the small lariosaur, which 

 measured about a yard in length, the limbs appear to have been somewhat 

 intermediate in structure between the clawless paddles of the true plesiosaurs 

 and those of more ordinary reptiles; and the creatures were probably amphibious 

 in their habits, spending part of their time on land, and part in the water. In the 

 allied nothosaurs and simosaurs the limbs were better adapted for walking, from 

 which we may infer that their owners were still more terrestrial in their habits. 



FRONT AND SIDE-VIEWS OF A NECK-VERTEBEA OF A PLESIOSAURIAN. 



UPPER ASPECT OF THE SKELETON OF THE LARIOSAUR, A SMALL PLESIOSAURIAN. 



