Loohing Backward 



mals remained few and insignificant, and then 

 in the Eocene spread with great rapidity, large 

 and varied forms springing into existence. 



So rapid, indeed, was the progress of mam- 

 mals in Tertiary times that each formation has 

 its own particular species, for new animals were 

 continually making their appearance. 



With few exceptions most of the orders of 

 vertebrates seem to have passed their culmina- 

 ting point, while many of them, like the laby- 

 rinthodonts, dinosaurs, and pterodactyls, have 

 long ceased to be. To-day, so far as may be 

 judged by fossils, those very different animals, 

 snakes and birds, are at their maximum. Birds 

 have spread completely over the earth, and the 

 highly specialized poisonous snakes with mova- 

 ble fangs are the highest as well as the most 

 recent of their class. 



Among the very noticeable changes that 

 have taken place, not only in the fauna of our 

 own continent but in that of the world, is the 

 disappearance of large animals. Aside from 

 the great bears which are confined to particular 

 localities, the bison, moose, and elk are the only 



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