47o 



THE JURASSIC PERIOD 



ceeded 25 feet. Baptanodon, found in Wyoming, is an Ichthyo- 

 saur without teeth and must have fed upon small and soft marine 

 invertebrates, as do the toothless whales. 



Another group of carnivorous marine reptiles is that of the 



Plesiosauria, which began in the 

 Trias and culminated in the Jura, 

 and which forms a curious contrast 

 to the Ichthyosaurs. In the typical 

 genus Plesiosaurus (Fig. 156) the 

 head is relatively very small, and the 

 £ jaws are provided with large, sharp 

 \ teeth, set in distinct sockets. The 

 neck is exceedingly long, slender, 

 J and serpent-like, and marked off 

 § distinctly from the small body. The 

 % swimming paddles are much larger 

 \ than in the Ichthyosaurs and proba- 

 \ bly had more to do with locomotion ; 

 1 the skeleton of the paddle departs 

 3 much less widely from the structure 

 3 of a terrestrial reptile's foot than 

 ~ does that of an Ichthyosaur. With 

 I their long necks, the Plesiosaurs 

 i could lie motionless far below the 

 5 surface, occasionally raising their 

 heads above the water to breathe, 

 or darting them to the bottom after 

 their prey, which consisted chiefly 

 of fish. The Jurassic species of 

 Plesiosaurus do not much exceed a 

 length of 20 feet, but Pliosaurus of 

 the same group was gigantic, a single paddle sometimes measuring 

 6 feet in length ; the reptiles of the latter genus had, however, 

 proportionately larger heads and shorter necks. 



The seas and rivers of Jurassic times were swarming with Croco- 

 diles, Teleosaurus being the characteristic genus of the period. In 



