206 LAND MAMMALS IN THE WESTERN HEMISPHERE 



extinct, but they long played a very conspicuous role in South 

 America, where they originated and whence the North American 

 representatives migrated. The fground-sloths were great, 

 unwieldy, herbivorous animals covered with long hair, and 

 in one family (fMylodontidse) there was a close-set armour 

 of pebble-like ossicles in the skin, not visible externally ; they 

 walked upon the outer edges of the feet, somewhat as the Ant- 

 Bear (Myrmecophaga) uses his fore paws, and must have been 

 very slow-moving creatures. Their enormous claws may have 

 served partly as weapons of defence and were doubtless 

 used also to drag down branches of trees and to dig roots and 

 tubers. Apparently, the latest of these curious animals to 

 survive was the very large ^Megalonyx, which, it is interesting 

 to note, was first discovered and named by Thomas Jefferson. 

 The animals of this genus were very abundant in the forests 

 east of the Mississippi River and on the Pacific coast, much 

 less common in the plains region, where they would seem to 

 have been confined to the wooded river valleys. The still 

 more gigantic ^Megatherium, which had a body as large as that 

 of an elephant and much shorter, though more massive legs, 

 was a southern animal and has not been found above South 

 CaroUna. ^Mylodon, smaller and lighter than the preceding 

 genera, would seem to have entered the continent earlier and to 

 have become extinct sooner ; it ranged across the continent, 

 but was much commoner in the plains region and less so in the 

 forested areas than \Megalonyx, being no doubt better adapted 

 to subsisting upon the vegetation of the plains and less de- 

 pendent upon trees for food. 



The fGlyptodonts were undoubtedly present in the North 

 American Pleistocene, but the remains which have been col- 

 lected so far are very fragmentary and quite insufficient to 

 give us a definite conception of the number and variety of them. 

 It will be better therefore to defer the description of these 

 most curious creatures until the South American Pleistocene 

 is dealt with, as they were incomparably more varied and 



