THE EVOLUTION OF THE MAMMALIA. 243 
less complete and satisfactory than in the case of the hoofed ani- 
mals, though the main facts of advance and differentiation are 
clearly enough displayed. Concerning the history of the small 
forms, such as the bats and insectivores, we have very little 
information indeed, while that of the great order of the gnawing 
animals (Rodentia), by far the most numerous of all mammalian 
orders, is still in a very confused and unsatisfactory state. On 
the other hand, the main outlines of the story of the flesh-eaters 
(Carnivora) have already been recovered. 
The most ancient group of the flesh-eaters is the extinct 
order Creodonta, which flourished exceedingly till the middle 
Eocene, but began to decline after it had given rise to the true 
carnivores, and became entirely extinct in the lower Miocene. 
The creodonts were a much diversified group, comprising several 
families, and were remarkable for their large, unwieldy heads, 
small and simple brains, numerous small teeth and primitive, five- 
toed, plantigrade feet. By plantigrade is meant that the whole foot 
was on the ground in walking, as in the bears, and the animal did not 
walk on the toes, as does the dog, for example. Most creodonts were 
quite small, but very large species have been found in the Wasatch 
and Bridger, which must have been exceedingly formidable beasts 
of prey. In Bridger times, or perhaps even earlier, the true car- 
nivores began to branch off from the creodonts ; but these early 
carnivores resemble their creodont ancestors so closely that any 
line of separation is quite arbitrary, and they are in all respects 
much more primitive than any existing flesh-eaters. In the upper 
Eocene of Europe, two carnivorous families, the dogs and the 
civets, are distinguishable, and in North America the dogs and 
possibly the civets also. In the Oligocene of both continents 
appear two additional families, the weasels and the cats, the latter 
represented only by the remarkable sabre-tooth series. In Europe 
the beginnings of the bear family, and in America of the raccoons, 
are to be noted in the Oligocene, while the remaining family of 
the land carnivores, the hyaenas, arose in the late Miocene or early 
Pliocene of the Old World. 
The history of the dogs (family Canidce), using that term in 
