518 LAND MAMMALS IN THE WESTERN HEMISPHERE 



Two families, the hyenas (Hysenidse) and civet-cats (Viver- 

 ridse), are omitted from the table because they apparently 

 never reached the western hemisphere. The bears, of Old 

 World origin, invaded America at a very late period and are 

 not certainly known here before the Pleistocene. The other 

 four families were well represented in North American history, 

 though the great weasel tribe (Mustelidse) went through the 

 greater part of its history in the Old World. None of the 

 families is indigenous in South America, and all of the five 

 families which it now shares with North America came in in 

 the series of immigrations, of which the first recorded effects 

 are found in the Pliocene and continued into the Pleistocene. 



The Fissipedia are adapted to a great variety of habits and 

 modes of life and consequently there is considerable diversity 

 of structure among them, though they all form a homogeneous, 

 natural group. The dogs (Canidse) are terrestrial, neither 

 swimmers nor climbers ; some, like the foxes, are solitary, 

 others, like the wolves, hunt in packs and nearly all are strong, 

 swift runners. The cats (Felidse) which have a remarkable 

 range of size, are terrestrial or arboreal ; they take their prey 

 by stalking and leaping upon it, not by running it down. The 

 bears (Ursidse) are mostly omnivorous, not very often killing 

 prey, and largely vegetarian in diet. The raccoons (Pro- 

 cyonidse) are chiefly arboreal and omnivorous. The very 

 large and varied weasel family (Mustelidse) have different 

 habits, though nearly all are fierce and bloodthirsty. 

 Otters and sea-otters are aquatic and prey chiefly on fish ; 

 minks and fishers are semi-aquatic ; martens are arboreal, 

 skunks terrestrial and badgers fossorial. 



While there is thus much diversity of habit with corre- 

 sponding differences of structure among the Fissipedia, there is 

 a certain unity of plan recognizable among them all. With 

 but few exceptions, the incisors are present in full number and 

 the canines are formidable lacerating weapons. Especially 

 characteristic of the dentition are the ''sectorial" or ''car- 



