164 MAMMALS OF THE PACIFIC WORLD 



have succeeded in establishing themselves when the world of 

 mammals was comparatively young. The classical example of 

 these is the pouch-bearing mammals of Australia. This land, 

 even though called a "continent" because of its large size, is in 

 reality a big, deep-sea island. Marsupials were present in 

 America, Europe, and probably Asia at the time when they are 

 believed to have reached Australia. Upon arrival they found a 

 fertile and varied territory probably devoid of mammalian 

 competitors. In their evolutionary experiments they produced 

 pouched replicas of flying squirrels and tree squirrels, mice, 

 lemurs, woodchucks, weasels, wolves, and moles. They failed 

 to develop either a marsupial bat or a marsupial swimmer. 



During the late prehuman and possibly early human period 

 of Australia, many giant marsupials, which apparently died 

 out rather recently, still existed. Huge hippopotamus-like ani- 

 mals, a marsupial "lion" (which probably ate vegetation), and 

 enormous kangaroos have left their bones in caves and in the 

 mud of dried-up lakes in Australia. New Guinea, representing 

 the tropical phase of the Australian fauna, has much the same 

 type of animals. 



Archaic animals of other islands are by contrast less arrest- 

 ing. It is unlikely that any other islands contain mammals 

 whose time of arrival dates as far back as the marsupial move- 

 ment. Random colonization of islands has been a continuous 

 process, and many animals that are not "recent" in terms of 

 existing continental forms can still be found on islands. Such 

 are the peculiar small cattle of the Philippines and Celebes, the 

 pig-like babirusa and the black ape of Celebes. Similarly, many 

 kinds of rat-like animals on those islands and also on New 

 Guinea and Australia no longer possess close relatives in Asia. 



BIOLOGICAL REGIONS 



The land surface of the globe is divided into five major zoo- 

 geographical regions, which include a number of subregions. 



