THE EVOLUTION OF THE MAMMALIA. 245 
their range into all the large land masses of the world. From 
some of the early aberrant dogs of the European Oligocene, was 
given off a side line which terminated in the bears (family 
Vrsidce). The steps of this transformation have not all been 
satisfactorily followed out, but it seems to have taken place within 
the Miocene, and was marked by the loss of the trenchant charac- 
ter of the molar teeth, which became more and more flattened 
and tuberculated, until they came to resemble those of the pigs, 
by the retention and exaggeration of the plantigrade gait, and by 
numerous minor changes of structure. The bears are thus an 
exclusively Old World family in origin and development, and 
did not reach North America until the great Pleistocene migra- 
tion. At present they are still characteristically northern in dis- 
tribution, not having found their way into Africa, and in South 
America they have only followed the great Andean mountain 
chain. 
The raccoon family (Procyonidcz) long remained a mystery, but 
the recent discoveries of Matthew have thrown a very welcome 
light upon the subject. It would seem that they originated in 
later White River times from certain small members of the dog 
family. They never spread very widely, nor did they give rise to a 
great variety of forms. At the present time they range over 
North, Central, and South America, and are mostly small, arboreal 
forms, but they have only one representative in Asia, the curious 
panda {Ailurus) which, in Pleistocene time extended westward to 
England. The three families of the dogs, bears, and raccoons 
are thus derived from a common stock, and are more nearly 
allied to one another than to the other families of the order. 
The civets (Viverridce) are of somewhat uncertain origin, 
though their earliest representatives draw very near to the smaller 
dogs of the Wasatch and Bridger, and it is possible that they first 
arose on this continent. However this may be, the chief devel- 
opment of the family took place in the eastern hemisphere, and 
no member of it has been found in America since the middle 
Eocene. The civets, on the whole, have undergone very little 
change, and in Europe they were abundant from the upper 
