82 RANGE OF MARSUPIALS CHAP. 



A third cause of more or less limited range is the barrier 

 due to competition. If the ground is already taken up, there is 

 no room for new immigrants. There is obviously a limit to the 

 number of Antelopes or Deer that can graze upon a given tract 

 of grassy plain. These two groups of Ungulates illustrate the 

 matter well: the Antelopes are African and Indian, especially 

 the former, while Africa has no Deer at all ; America, on 

 the other hand, has plenty of Deer but no Antelopes, save the 

 Prong-horn. The more nearly akin the two species or groups 

 of species are, the fiercer will be the competition ; for a near 

 kinship will at least often imply similar habits, the need for 

 similar food, and other likenesses which will prevent both from 

 successfully occupying the same tract of country. The remark- 

 able fauna of Australia is believed to afford an example of this. 

 In that country the prevalent inhabitants are the Marsupials. 

 The Monotremes are found there also, and nowhere else save in 

 New Guinea and Tasmania. The remaining mammals are in- 

 conspicuous ; they embrace a few Kodents and Bats, and the 

 doubtfully indigenous Dingo -dog. Now the Marsupials are 

 fitted to every variety of life. We have the grazing Kangaroos 

 and Wallabies, the burrowing Wombats, the arboreal Phalangers, 

 and the carnivorous Dasyures. In the second place, it is an 

 unquestioned fact that the Marsupials are an older race than 

 are the existing Eutherian mammals ; they were the dominant 

 mammals during the Secondary epoch. At that time they were 

 more widely distributed than at present. In most parts of the 

 world they are now absent, since they have been successfully 

 ousted by the more highly organised groups of Eutheria. But at 

 that period, when the higher Eutheria were in the ascendant, 

 Australia and the islands to the north became cut off from Asia, 

 and thus became freed from inroads of Eutheria, which were 

 partly prevented by the physical barrier of the sea from effect- 

 ing a settlement, and partly perhaps prevented owing to the 

 ground being already taken up by the Marsupials. Likeness 

 of habit gave the older inhabitants victory in the struggle for 

 existence. 



The general statements that have been here made are in 

 accord with current opinion upon the factors of geographical 

 distribution. But the past range of animals appears to be 

 less consonant with the received views. In the Tertiary 



