Animals Before Man 



their class on account of their high degree of 

 specialization, their entire skeleton being modi- 

 fied to adapt them to life in the air. They 

 depart most from the general structure of the 

 class, are more unlike the composite picture we 

 have in mind when we say reptile. Like the 

 plesiosaurs, they seem to have been a little 

 slow in reaching America, for while they were 

 abundant in Europe during the Jurassic period, 

 here they are rare until the Upper Cretaceous 

 is reached. In time we may be able to trace 

 the route by which they passed from the Old 

 World to the New, but now we can only say 

 that around the inland sea they reached an ex- 

 traordinary degree of development in numbers 

 and size. They were not present, however, in 

 as many curious forms as in Europe, for Pro- 

 fessor Williston recognizes but two genera, 

 Nyctodactylus and Ornithostoma,\)oi}i of which 

 were toothless. But if our dragons of the air, 

 as Professor Seeley calls them, were few in 

 species, they make up for it in the size of the 

 individuals, for Ornithostoma was the largest 

 of flying creatures. A large condor spreads 



210 



