The science of life : fully illustrated in tone and line and including many diagrams

THE EVIDENCE FR

land had been cut off by a barrier of ocean from all the continents, we should not expect to find any land-mammals in New Zealand. If lung-fish were once widely distributed all over the world, but later were all but extinguished in the struggle for existence, we should expect to find the few existing lungfish scattered in isolated regions which happened to favour their survival; it is along such lines that our reasoning must run.

The key to the present distribution lies in past distribution. When paleontology and geology are able to provide us with evidence, the distribution of animals and plants ceases to be a puzzle and becomes a simple matter of history. In the same way the distribution of

human races, often so Greenland puzzling at first sight, and clears up _ directly Eastern we know the history North

of their movements.

The Mongol Turks in Asia Minor, or the fair-haired Lombards in Northern Italy, are at first sight anomalies; but with a knowledge of their migrations, the problem disappears. The only difference with animals and plants is that the periods of time involved are so huge that transformation as well as mere migration of stocks comes into play.

With these ideas in

Fig. 146.

(IV C).

mind, we can turn back to the three southern continents

and their three wholly different sets of animal inhabitants. First comes Australia and its marsupial menagerie. During most of the late Mesozoic Era (IV), Australia was connected with the rest of the world. Whether there existed a land-bridge to Asia, or, as many are inclined to believe, to Antarctica and thence again up to Cape Horn, or whether, as Wegener thinks, it once formed a part of a great southern continent which was later broken up, we must leave to the geologists to settle ; in any case it is immaterial to us. We know that true placentals did not appear on earth before the later Cretaceous (IV C), that the earlier, Mesozoic (IV), rammals were akin to monotremes and to marsupials,

America

Srnas being ited. much of Europe, chalk was being deposited. I f No America connected with Europe, but the Cretaceous marsupials were able to pass across from the Eurasiatic land-mass to Australia.

broken, and Australia isolated.

OM LIVING THINGS

though mostly even more primitive in type, and occurred all over Europe and North America. All of them, however, were very small, and they showed little variety in their ways of life. Some time in the Cretaceous (IV C) these primitive marsupial and monotreme mammals penetrated into Australia ; the land-connection between it and the rest of the world was broken, before any placentals could enter. Australia thus became the marsupial’s Ark—with the important difference that they did not stay merely a year and ten days in it like the animals in Noah’s Ark, but over fifty million years. Indeed, it was to them like a combination of Ark and Promised Land. For

Spitsbergen é&

Northern Europe

Northern and Central

How the Marsupials colonized Australia.

The probable distribution of land and sea about halfway through the Cretaceous Period In the shallow seas extending over what are now Western America and

Not only was the main block of North

This land-bridge was soon afterwards (Modified from Schuchert.)

during that long time they flourished and were able to give rise to new and varied forms of life not found in any other region of the world. These possibilities of the pouched mammal were never realized elsewhere, since in all other regions the marsupials were kept from rising or exterminated by the competition of the placental hordes, biologically more efficient in the protection of their unborn young and in the construction of their brains.

Now that modern man has introduced placentals into Australia, the marsupials are no match for them, and are dying out. — The development of the varied marsupial life of Australia was due to biological Protection.

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