520 



THE THEORY OF EVOLUTION 



geologic epochs. Hence, the problems of Paleontology are insep- 

 arable from those of Zoogeography, or the geographical distribution 

 of animals at the present day. The camel family illustrates this 

 inter-relationship. Approaching the problem from the standpoint 

 of present geographical distribution, this family consists of two 

 types which are widely separated. The genus Camelus, which 



Fig. 279. — Archasopieryx, the earliest bird. 



Left, one of the fossils as preserved in fine-grained stone. Right, a reconstruction of 

 this fossil. The feathers and general shape of the body are those of a bird, but the teeth, 

 the tail, the claws on the wings, and other features are reptilian. (Left, from Lucas, 

 "Animals of the Past," courtesy American Museum of Natural History; right, from Parker 

 and Haswell, "Textbook of Zoology," copyright, 1921, by Macmillian & Co., Ltd., reprinted 

 by permission.) 



includes the animals popularly called " camels," consists of two 

 species: the one-humped Arabian camel, or dromedary; and the 

 two-humped Bactrian camel of Central Asia. On almost the oppo- 

 site side of the world, in the Andes of South America, are the only 

 other camel-like animals that are now in existence: the genus 

 Auchenia, with its two species, the guanaco and the vicugna; and 

 their domesticated descendants, the llama and the alpaca. The 

 wide separation of these two genera of a single family is surprising, 



