THE CRETACEOUS PERIOD. 



179 



gavials. A few small salamanders, of modern type, are known from 

 the late Cretaceous. 



The Pterosaurs. — The flying reptiles made so distinct an advance 

 in specialization, that Williston regards them as having come to excel 

 all other volant vertebrate animals. Some attained a wing-spread 

 of perhaps 20 feet, and had great powers of flight. In the genera 

 Pteranodon and Nyctosaurus (Fig. 412) the development of the anterior 

 parts was disproportionately great, while the posterior parts were 

 very small and weak, so much so that it is doubtful whether they 



*^% 



Fig. 412. — A Cretaceous Pterodactyl, Nyctosaurus gracilis Marsh, about one-ninth 

 natural size, from Niobrara Cretaceous, Kansas. (Restored by Williston.) 



could stand on their feet alone. That they had powerful and sus- 

 tained means of flight, is implied also by the occurrence of their remains 

 far from shore. In Cretaceous times, they were all short-tailed, and 

 for the most part toothless, though the toothed forms persisted for a 

 wnile. Their bills resembled those of modern birds, and they have 

 been styled the kingfishers of the Cretaceous seas. If these forms 

 were the sole ones, the pterosaurs might well be classed with the sea 

 life. 



Terrestrial birds undoubtedly existed, but the record is negative, 

 while curious aquatic forms appeared, which will be treated under the 

 sea life. 



The slight progress of the mammals. — The mammals thus far 

 recovered from the Belly River and Laramie Cretaceous deposits 



