CHAPTEE XVII 



THE BIRDS 



189. Characteristics. Birds form one of the most sharp- 

 ly defined classes in the animal kingdom, and the variations 

 among the different species are relatively small. "The 

 ostrich or emu and the raven, for example, which may be 

 said to stand at opposite ends of the series, present no such 

 anatomical differences as may be found between a common 

 lizard and a chameleon, or between a turtle and a tortoise," 

 and these we know to be relatively slight. 



In many respects the birds resemble the reptiles, and 

 long ago in the world's history the relationship was much 

 closer than now, as we know from certain fossil remains in 

 this country and in Europe. One of the earliest of these 

 fossil birds, that of the Archaeopteryx, is a most remarkable 

 combination of bird and lizard. Unlike any modern bird, 

 the jaws were provided with many conical reptile-like teeth. 

 The wings were rather small, and the fingers, tipped with 

 claws, were distinct, not grown together, as in modern birds. 

 The tail was as long as the body, and many-jointed, like a 

 lizard's, each vertebra carrying two long feathers. The 

 bird was about the size of a crow, and it probably could 

 not fly far. Other ancient types have been discovered 

 principally sea-birds many of which existed when the 

 Pacific extended over the region now occupied by the 

 Eocky Mountains. These were all of the same generalized 

 type, intermediate between reptile and bird. This fact 

 leads us to the belief that birds descended from reptilian 



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