SUCCESSIVE MAMMALIAN FAUNAS 205 



inated. Their absence from the older Pleistocene (Equus 

 Beds) may be accounted for by the fact that those beds con- 

 tain a fauna of the open plains, while bears are chiefly forest- 

 living animals. An extinct type of the family is the group 

 of species which constitute the fshort-faced bears {^Arctoiherium) , 

 very large and powerful creatures, with remarkably shortened 

 jaws, which have been found from ocean to ocean. The smaller 

 beasts of prey, badgers, weasels, etc., were, as intimated above, 

 substantially the same as now. 



The rodents of the Pleistocene were very nearly in their 

 modern stage of development, most of the genera and many 

 of the species surviving to present times. Just what members 

 of the order were introduced from the Old World, the imperfect 

 and fragmentary history will not permit us to say, but some 

 interesting South American immigrants should be noted. One 

 of these, the Capybara or so-called Water-Hog (Hydrochoerus 

 capybara), the largest of existing rodents, failed to gain a per- 

 manent foothold, but another South American form, the Short- 

 tailed or Canada Porcupine {Erethizon dorsatus), common 

 all over the United States in the Pleistocene, has maintained 

 itself to the present day. One especially peculiar form, not 

 derived from South America or the Old World, is the fGiant 

 Beaver {'fCastoroides), one species of which, fC ohioensis, was 

 as large as a Black Bear and occurred in the later Pleistocene, 

 while a smaller species ("fC. species indet.) is found in the more 

 ancient deposits of the epoch. In almost all respects fCas- 

 toroides was simply a gigantic beaver, but the grinding teeth 

 were remarkably like those of the South American Capybara 

 (Hydrochoerus), so much so that it has been mistakenly re- 

 ferred to the same family by some authorities. 



By far the strangest elements of the Pleistocene faunas 

 were the two suborders of gigantic edentates, the fGravigrada, 

 or tground-sloths, and the fOlyptodontia, which might well be 

 called giant armadillos, if that name were not already in use 

 for a living Brazilian animal. Both suborders are completely 



