HORN EXPEDITIOX—MAMMALIA. 
5 
Tlie changes resulting in the loss of humidity and the comparatively rapid 
drying-up and conversion of the country into a more or less arid region went hand- 
in-hand with the extinction of the old fauna. It is scarcely possible to imagine 
that many of the mammals would be able to accommodate themselves to such a 
complete reversal of climatic conditions as evidently took place in Central Australia, 
and more especially in the southern, central, and western parts, which now form 
what Professor Tate has called the Eremian region.* 
It was at this time, when the physiographic conditions of the continent became 
changed, that the distribution of the marsupial fauna, as we now find it, must have 
been determined, at all events in its broad outlines. 
The remains of extinct diprotodonts, evidently existing in large numbers, show 
that there must have been a very considerable land area in the central parts 
suitable for habitation, and in all probability alFording a means of communication 
between the eastern and western parts of the continent. This diprotodont fauna 
probably spread across from the east to the west, and thus A¥estern Australia 
received the ancestors of its present diprotodonts. Climatic changes in Tertiary 
times led to the drying-up of the central and western parts of the continent, until 
linally these parts became to a large extent waterless ; surrounding them was 
formed a broad belt of comparatively dry country, whilst the humid and more 
fertile parts were confined to the littoral regions rising inland into mountain ranges 
and running along the north, east and south-east coasts. To this Professor Tate 
has given the name of Euronotian region. In the south-west lies a similar district— 
the Autochthonian. 
So far as the marsupial fauna is concerned we can divide Australia into two 
main regions, the first of which corresponds to the Euronotian region, while the 
second includes the remainder of the continent. The Autochthonian renion, which 
is so strongly marked in the case of plants, cannot, so far as marsupials are 
concerned, be regarded as distinct. It has certainly a few distinctive forms, but 
these are principally to be found amongst the more specialised diprotodonts. Its 
marsupial fauna in no way stands in the same relationship to that of the rest of 
the continent as does its flora. So far as it is known it is closely allied to that of 
the great mass of country which stretches right across to the inland boundary of 
the Euronotian region. 
There is again no distinctive Eremian marsupial fauna, but there is, on the 
other hand, a very distinct one which is characteristic of the broad belt of country 
in which the I’ainfall is between ten and twenty-five inches yearly. 
*■ Aust. Ass. Adv. Sci., Sydney, 1888, vol. i. Presidential Address to the Bioloj,dcal Section, p. 312, pi. xviii. 
