THE CHANGING WORLD OF LIFE 



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period of separation, the groups would certainly show differences from 

 one another and the changes might even be so extensive that they would 

 be classified as different species. This is what happened to the rabbits 

 at Porto Santo, but since natural spread and adaptation of animals is 

 slow, we usually have to study animals in their present environment and 

 see how they differ from their ancestors in other localities. 



Photos by Winchester 



Fig. 34.14. Fossil remains of prehistoric ancestral horses. At left, small skull and 

 front and hind feet of Eohippus, which lived on the earth about 35 million years ago. 

 It was only the size of a fox terrier dog and had four toes on the front legs and three 

 on the hind legs. At right, skull and foot of Mesohippus, which lived about 30 million 

 years ago. It was about the size of a collie dog and had three toes on both front and 

 hind feet, but the center toe was much larger than the other two. 



The camels serve as a good illustration of adaptations to different 

 environments. The one-humped Arabian camel has lived in the desert 

 and is well adapted for such life. There are broad pads on its feet which 

 give it traction in the sand, there are pouches in its stomach which store 

 water, and extra food is stored in the hump. The two-humped Bactrian 

 camel lives in more northerly regions and has developed long shaggy 



