HISTORY OF THE CARNIVORA 553 



tigers {'\Smilodon) and short-faced bears {'\Arctotherium) were 

 shared with North America. In the Pliocene a bear, a raccoon 

 and a dog were the only known fissipedes, and in the 

 Miocene none have been found, their place being taken by 

 flesh-eating marsupials. 



While the history of the Fissipedia, as outlined in the pre- 

 ceding pages, is sadly incomplete as compared with that of 

 many ungulates, it is nevertheless highly suggestive. In each 

 family the advance of speciaUzation and adaptation to a 

 narrow range of habits may be followed ; generally speaking, 

 the teeth were diminished in number and increased in size and 

 were either simplified by the loss of parts, as in the cats, or 

 complicated by the addition of new elements, as in the bears 

 and raccoons. The brain grew larger and more convoluted 

 and the cranium more capacious; in most of the famiUes, 

 the face was shortened, notably in the cats and mustelines, 

 while in others, especially the dogs, it was elongated. In all 

 of the early types there was a long and heavy tail, but in most 

 series it underwent more or less reduction. There was little 

 reduction of digits, and no fissipede has less than four. In 

 modern dogs and cats there are five digits in the manus and 

 four in the pes and the hyenas have four in each, as has one 

 genus of mustelines ; other modern genera throughout the sub- 

 order are pentadactyl. 



It is significant that the more ancient members of the various 

 families differed less than do the modern ones; the various 

 groups, as they are traced back in time, would seem to' be 

 converging to a common ancestry, of which the lower Oligocene 

 dogs were the least changed representatives, and it is probable 

 that all the famiUes of the Fissipedia were derived, directly 

 or indirectly, from a single Eocene group of primitive flesh- 

 eaters. The families, none of which is extinct, are not all of 

 equal antiquity. So far as now appears, the dogs and viverrines 

 are the most ancient, having become distinct in the upper 



