CHAPTER XX. 



The Birds. 



"D EFORE taking up a study of the last and greatest class 

 in the tree of animal life, the mammals, it is instructive 

 to note the cumulative evidence presented by the birds in a 

 story of Evolution. In an outline such as this volume is 

 intended to be, they shall only be considered in their relation 

 to adaptation and environment; of the part they play in the 

 Plan of Creation and of their importance to all life, both 

 plant and animal. Birds are the warm blooded near rela- 

 tives of the reptiles. Their toothed, reptile-like ancestors 

 began to change their scales into feathers and fossil evidence 

 has been found in that of the Archaeopteryx which was appar- 

 ently half bird and half lizard and having a tail as long as 

 the body with two long feathers growing from each vertebra. 

 This proves their ancestry. We have seen that their fore- 

 limbs have been developed into wings by their constant flap- 

 ping while chasing their food or escaping from their enemies. 

 In these fossil birds the wings were not as yet fully developed 

 and the claws on the fingers were distinct in what is now the 

 wing tip of all true birds. 



These were the connecting link intermediate between 

 reptiles and birds. These ancestors of the birds developed 

 a four-chambered heart that started their development along 

 a branch contemporaneous with but different from the branch 

 that has been followed by the mammals. The food supply 



[216] 



