LIFE 55i 



hud dominated the Jurassic sea lived on into this period. The 

 former berame insignificant soon after its beginning; but the plesio- 

 saurs attained their highest development and perhaps their greatest 

 size at this time. The American plesiosaurs indicate lack of inter- 

 migration between this continent and Europe. 



The aquatic branch of the scaled saurians (Squamata) became 

 veritable sea serpents. The long-necked, lizard-like reptiles of the 

 Comanchean period were the forerunners, and perhaps the direct 

 ancestors, of a family (the mosasaurians, Fig. 465) which flourished 

 in the Cretaceous, and ranged from the Americas to Europe and 

 New Zealand. Their short career seems to have ended with the 

 period, and no direct descendants are known. 



Marine turtles seem to have appeared first in this period, and to 

 have had many forms. Some of them had skulls larger than those 

 of horses, and their shells must have been fully twelve feet across. 



Fig. 466. Champsosaurus, from the Laramie of Montana. Length, about six 

 frrt . (After Brown.) 



In the long interval between the first known appearance of birds 

 in the Jurassic, and the later Cretaceous when they reappeared, 

 important changes took place, among which was the loss of the 

 elongate, bilaterally feathered tail. The Jurassic birds were terres- 

 trial, while the Cretaceous were aquatic. The Cretaceous birds 

 include about 30 species belonging to two widely divergent orders, 

 Hesperornis and Ichthyornis. The former (Fig. 467) were large, 

 flightless divers, with aborted wings and remarkable legs. The legs 

 were not only very powerful, but the bones of the feet were so joined 

 to them as to allow the feet to turn edgewise in the water when 

 brought forward, thus increasing their efficiency as paddles. Fur- 

 thermore, the legs were so joined to the body frame as to stand out 

 nearly at right angles to it, like a pair of oars, instead of being under 

 the body like walking legs. Apparently, walking as well as flying 



