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 end 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 lkenesses 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 Rodents 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 
eround 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 
