THE JURASSIC PERIOD 411 



FIG. 435. The largest of the pterosaurs. A Cretaceous species. (Painted 

 by C. R. Knight, under the direction of Professor H. F. Osborn. Copy- 

 right by Amer. Mus. of Nat. Hist.) 



In the shallow waters along the seacoasts and in the 

 marshes of the rivers and inland bodies of water, other reptiles 

 which had adopted an aquatic mode of life were abundant. 

 Some, like the turtles and crocodiles of to-day, divided their 

 time between the water and the shores, and were provided 

 with legs fairly well adapted for either situation ; while others, 

 as described in the last Chapter, had become adapted for 

 swimming only. Their feet had been changed into flippers 

 not unlike those of a whale, and in the extreme examples of 

 this adaptation, only the front pair of paddles remained. 

 The rear pair, being apparently less useful, had gradually dis- 

 appeared, as in the modern whale. In such types the loss of 

 the rear legs was always compensated for by the develop- 

 ment of a long and powerful tail, flattened so as to serve as an 

 efficient propeller. 



The mammals still in the background. The birds and 

 mammals have been casually mentioned as occupying a 



