TERTIARY FAUNAS. 11 



that inhabit the region are already represented in deposits of the 

 early Pliocene period ; and in Australia the abundant remains of 

 Marsupialia amply testify to the identity of character which unites 

 the faunas of the past and present periods. A certain amount of 

 antiquity is thus established for the several regional faunas. The 

 farther back in time we proceed, however, the less pronounced ap- 

 pear the common characteristics of past and present periods ; and, 

 finally, they disappear almost altogether. Thus, the Eocene shell- 

 fish fauna of the Atlantic coast of the United States and of France 

 and Great Britain is very unlike that of the seas adjoining those 

 regions at the present day, although, in a measure, it finds its ana- 

 logue in the corresponding fauna of the eastern tropical seas. The 

 Miocene mammals of the American continent are almost wholly 

 unlike those which now inhabit the region, and what little simi- 

 larity still remains completely vanishes with the animals of the 

 more ancient Eocene period. And the same holds good with the 

 European Tertiary fauna. Yet there are a number of existing 

 types which in their own region can be traced through a series 

 of progressive modifications to ancestral forms more or less unlike 

 them, which belong to a comparatively remote geological epoch. 

 The horse of the Old World, for example, has been traced through 

 a number of intermediate forms to the Old Tertiary Palaeotherium, 

 one of the most abundantly represented mammalian genera of the de- 

 posits of Western Europe. The deer of the same region finds early 

 ancestors in the horned and hornless species which occur fossil in 

 the Miocene deposits of France and Germany ; and not unlikely the 

 wolf and fox see their progenitors among the early members of the 

 canine race, whose remains have been traced to the Oligocene, and 

 not impossibly also to the Eocene period. In so far as these ani- 

 mals are concerned, therefore, we have direct evidence of a fauna 

 of considerable antiquity developing in place. In other cases, how- 

 ever, evidence of a very opposite character is often presented ; that 

 is to say, faunas, or their components, are very frequently shown 

 to be in a given region of only brief duration. Thus, although 

 bears are very plentiful at the present time in the North American 

 continent, they are not known to have existed there before the last 

 geological period, the Post-Pliocene. And the same is true of the 

 members of the ox-family (Bovidae) most of which are, indeed, 

 not represented at all as fossils of which North America possesses 



