^^^ ZOOGENESIS '^'^^^ 



dinosaurs, duck-billed dinosaurs, and, together with 

 these, terrible predacious dinosaurs with a formidable 

 array of long sharp teeth. The giants of this group 

 were the great swamp-living dinosaurs with absurdly 

 small heads, enormously long necks and tails, heavy 

 bodies, and ponderous legs. 



The birds which lived in the Cretaceous period were 

 curious things with teeth like reptiles, quite different 

 from any of the birds we know at the present time. 

 But more important than the birds were strange flying 

 reptiles with wings much like the wings of bats. 

 These bat-like reptiles are known as pterosaurs. 

 Some of them were small, no larger than a sparrow, 

 but some were very large, as much as twenty-seven 

 feet across the expanded wings. 



Competing with fishes in the sea were plesiosaurs 

 of various kinds, and also mososaurs, as well as large 

 sea-turtles. Some of these last were more than twelve 

 feet long. 



Together with these curious types of reptiles lived 

 many other forms almost equally bizarre, but also 

 many of the more familiar types, as for instance 

 crocodiles and alligators. 



In spite of the great and striking differences between 

 most of the vertebrates of the Cretaceous period and 

 those of the present day, they are all instantly recog- 

 nizable as vertebrates as vertebrates are defined on the 

 basis of their representatives of the present day. 



Of all invertebrate fossils none are more familiar 

 than the remains of those curious crustaceans known 

 as trilobites (fig. 31, p. 55). All of the trilobites are 



