128 DISTRIBUTION OF EXTINCT ANIMALS. [PART II 
Lemurs and Marsupials—proves, that we have here hardly made 
an approach towards the epoch when the mammalian type itself 
began to diverge into its various modifications. Some of the 
Carnivora and Ungulates do, indeed, exhibit a less specialised 
structure than later forms; yet so far back as the Upper 
Miocene the most specialised of all carnivora, the great sabre- 
toothed Machairodus, makes its appearance. 
The Miocene is, for our special study, the most valuable and 
instructive of the Tertiary periods, both on account of its 
superior richness, and because we here meet with many types 
now confined to separate regions. Such facts as the occurrence 
in Europe during this period of hippopotami, tapirs, giraffes, 
Tragulide, Edentata, and Marsupials—will assist us in solving 
many of the problems we shall meet with in reviewing the 
actual distribution of living forms of those groups. Still more 
light will, however, be thrown on the subject by the fossil forms 
of the American continent, which we will now proceed to 
examine. 
