514 THE JURASSIC PERIOD 



the reduction of the outline of the body to fish-like lines and propor- 

 tions, in the sharp down-bending of the vertebrae at the end of the 

 tail for the support of a caudal fin, in the long snout set with teeth 

 adapted to seize and hold slipping prey, but not to masticate it, in 

 the protection of the eye by bony plates, and, interestingly enough, 

 in the development of a viviparous habit that freed them from the 

 necessity of returning to land to deposit their eggs. That their food 

 consisted in part of invertebrates is evident from the fossil contents 

 of the stomachs, the remains of 200 belemnites having been found in 

 a single one. There were small as well as large forms of ichthyo- 

 saurs, some exceeding 30 feet in length. 



Descended from a different stock, the plesiosaurs (Fig. 437) 

 adapted themselves to sea life in another way. The body took on a 



Fig. 437. Skeleton of Plesiosanrus dolichodeirus Conyb. (Restored by Cony- 

 beare.) 



form like that of a turtle, while the neck was elongate, giving rise 

 to the epigrammatic description "the body of a turtle strung on a 

 snake." Swimming was chiefly by means of paddles, though some 

 forms had a fin-like adaptation of the tail. The elongation of the 

 neck was variable, the vertebrae of the neck numbering from 13 to 

 76. The neck appears not to have been so flexible as familiar 

 illustrations have represented it, nor were the jaws separable and 

 extensible as in the case of snakes. This implies either that they 

 lived on small prey, or tore their food to pieces before swallowing. 

 They were doubtless formidable foes of the smaller sea animals, but 

 probably not of the larger. Like ichthyosaurs, they were without 

 scales. They ranged from 8 to 40 or more feet in length. 



Marine crocodilians made their appearance late in the period. 

 They had undergone a remarkable adaptation to the sea (Fig. 438). 

 They were fish-like in appearance, their skins were bare, and their 

 tails terminated in a fin like that of the ichthyosaurs. The fore 

 limbs were short and paddle-like. The hind limbs were modified 



