670 



HISTORICAL GEOLOGY 



Edentates. — This class is found abundantly in the Tertiary for- 

 mations of South America, and towards its close developed into gigan- 

 tic and highly specialized forms which were among the largest animals 

 of that continent. The Pliocene land connections between North 

 and South America permitted some of these large creatures to im- 

 migrate to North America, where they lived into the Pleistocene. 



Fig. 578. — Restoration of the gigantic sloth, Megatherium. (After Prof. W. D. 

 Scott, History of Land Mammals.) 



They never reached the Old World, and in South America their living 

 relatives are small and inconspicuous. Some of the Megatherium 

 (Greek, megas, large, and therion, a beast) tribe (Megatherium, Mylo- 

 don, Megalonyx) which reached this continent attained the bulk 

 of a rhinoceros. What strikes one most in examining the skeleton 

 of a Megatherium (Fig. 578) is its pyramidal shape, the hind legs 

 being massive as compared with the fore, and the backbone rapidly 

 enlarging toward the hind quarters. The Megatherium lived upon 

 leaves and twigs, and when standing on its hind legs could, if neces- 

 sary, use its tail as the third leg of a tripod, leaving the fore limbs free 

 to pull down blanches or even trees of considerable size. 



