336 GENERAL ZOOLOGY 



though there were many relics from previous ages, the great 

 majority of animals were much like those of today. 



QUATERNARY AGE 



Pleistocene Period. This was a time of great temperature 

 changes, and the northern hemisphere was invaded four 

 times by great masses of ice which came from the north. 

 Climatic conditions caused great migrations among animals. 

 Europe, for example was at times inhabited by reindeer, 

 arctic foxes, musk-oxen, woolly rhinoceri, mammoths, and 

 other animals characteristic of cool regions. When the ice 

 receded, horses, elephants, sabre-tooth tigers, lions, hippo- 

 potami, and other animals came in. During the warm 

 interglacial periods several races of men dwelt in Europe 

 and attained a considerable degree of primitive culture. 

 In South America giant sloths, peculiar camel-like creatures, 

 and gigantic armadillos (Fig. 113) were still in existence. 



Since the last great glaciation the northern hemisphere 

 has enjoyed a fairly stable climate, vegetation has spread 

 northward, and animals have increased in numbers. The 

 most important feature of the Quaternary Age has been 

 the rise of man and his domination of the earth. 



PAL^ONTOLOGICAL HISTORY OF ELEPHANT AND HORSE 



The discussion of the geological periods necessarily has 

 been very limited and noted only a few of the important 

 events of palseontological history. In order to give a more 

 concrete idea of how modern types of animals have de- 

 veloped from primitive ancestors, two of the best known 

 series will be briefly described. These relate to the ances- 

 tors of the elephant and the horse. 



The earliest elephant remains (Fig. 114, A) were dis- 

 covered in Middle Eocene deposits in Egypt. The crea- 

 tures from which modern types probably descended were 

 small tapir-like animals, about three and a half feet high, 

 which appear to have dwelt in swamps, living upon the 

 succulent, semi-aquatic herbage of that time. Their front 



