THE LIFE OF MAMMALS 
distributional zodlogy; and since this importance was first demonstrated 
and explained by the great explorer and naturalist, Dr. A. R. Wallace, it 
is now by common consent appropriately denominated ‘Wallace’s Line.’ 
To the eastward marsupials extend as far as New Ireland and the Solo- 
mon Islands, but they are unknown in Polynesia proper, as, indeed, 
they are in New Zealand, where, by the way, there are no indigenous 
mammals at all.” 
This localized condition of a great group is explained by the 
statement of scientists that Australia and its neighboring islands 
were connected with Asia previous to the Jurassic period, but 
since that time have been separated from it by the deep chan- 
nels along Wallace’s Line; at that time Australia seems to have 
been much more extensive than at present, embracing within its 
mainland Tasmania, New Caledonia, and other present islands. 
It is a fair inference that previous to and during the Jurassic 
period Australia, as a part of the Asiatic continent, became 
peopled with the only mammals then in existence — the small 
primitive marsupials. Then the island-continent was cut off, 
and they were left to work out their destiny undisturbed by any 
immigration of alien competitors or destructive enemies. To 
this fortunate isolation, perhaps more than to anything else, 
they owe their immeasurably long survival, for before the close 
of the next era the influences and competition abroad in Europe 
and Asia had killed off all the marsupials that had remained 
there. A similar fate seems to be slowly overtaking the long- 
preserved Australian remnant, apart from anything man is 
doing. ‘There is evidence of the existence during the Pleistocene 
of many now extinct forms of kangaroos and wombats, by the 
side of which the largest existing species would be as dwarfs. 
“The cause of this universal extinction (for universal it is) of 
the most gigantic mammals throughout the world soon after 
man made his appearance on the earth is one of those problems 
which has not yet received a satisfactory answer, as not even a 
glacial period could have made a clean sweep of the whole 
globe.” Such is the substance of the present view. 
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