3*4 



THE POPULAR SCIENCE MONTHLY 



Psychozoic. < 



i -=== -Terti ary. 



~&<vsmi 



x 



-Cretaceous 

 (Hesperornis, 

 Ichthyornipj. 



J S ".''.'.' -Jurassic 



Aw-HgSs&gl (Arcbaeopterys). 





common with the warm-blooded, feathered inhabitants of the air ; 

 and yet onr first scientists, for instance, Prof. Huxley, unite rep- 

 tiles and birds as one class of ani- 

 mals. However closely we may 

 study the anatomy of a chicken 

 and of a crocodile, and search for 

 points which are common to both, 

 we shall be only moderately in- 

 clined to follow the example of 

 these naturalists and consider 

 birds and reptiles as near rela- 

 tives. But we shall become con- 

 vinced of their close connection 

 if we study also their geological 

 history. 



In the first instance, we then 

 see that the reptiles of the present 

 time are only small remnants of a 

 once numerous and powerful tribe. 

 In certain former geological pe- 

 riods we find reptiles to be the 

 kings of the earth ; we discover 

 reptiles of enormous sizes ; rep- 

 tiles of all kinds of shape and ana- 

 tomical construction ; and among 

 them there are some which resem- 

 ble birds much more than does a 

 crocodile or a lizard of the present 

 day. In the second instance, if we 

 look at the birds of former periods 

 we find that, in the same way as 

 we go backward in the history of 

 our earth, these former inhabitants 

 of the air differ more and more 

 from the specialized pattern after 

 which all our present birds are 

 built, that they become more and 

 more reptile-like, and that there 

 can hardly be any doubt that the 

 birds are indeed branched off from 

 the great reptilian trunk of the 

 animal kingdom. 



There are three fossil birds of 

 pretertiary age known almost com- 

 pletely ; two of them were found in the Cretaceous formation of 

 North America, and one in the Jurassic formation of Germany. 



&SI 



Fig. 2. Section of the Earth's Crust. 



