
10 A FIRST CHAPTER 
where the reasons for the restriction of animals to certain places are by no 
means evident. Great bodies of water are most effectual barriers to 
the spread of many animals, some are hemmed in by mountain ranges, 
others by deserts, but back of such obvious causes lies the all-important 
question of food, and this, so far as land animals are concerned, depends 
on temperature, which determines the distribution of plants and of the 
animals directly or indirectly dependent on them for subsistence. 
New Zealand and Australia are the most striking examples of the 
effect of wide stretches of water on the distribution of animals: for, save 
two species of bats, not a single mammal is found in New Zealand, while 
the mammalian fauna! of Australia consists almost entirely of marsupials, 
the only other land animals being the dingo, or wild dog, supposed to 
have been introduced by man, and a few little rodents. In the first case 
it is inferred that if New Zealand has ever been connected with any 
other land, it was before the appearance of mammals on earth; in the 
latter instance, the deduction is that Australia has been isolated since the 
Cretaceous Period, when the lower types of mammals had appeared, and 
that its peculiar assemblage of animals is the result of evolution within 
its own boundaries. 
A very important point that must be taken into account in dealing 
with the distribution of existing animals is the distribution of extinct 
animals: for this often accounts for the presence of related species in 
widely separated parts of the world. Tapirs are examples of this dis- 
continuous distribution, one species being found in Malaysia, while the 
others dwell in the warmer parts of America. These places are widely 
separated, and by no possibility could these animals now pass from one 
locality to the other; but remains of fossil tapirs or tapir-like animals are 
found in various parts of the world: so we know that existing tapirs are 
the survivors of a once numerous race of animals. 
Such cases as this are taken as evidence of the former union, direct or 
indirect, of countries now widely separated, some animals being much 
more important witnesses than others. Birds, which pass over long 
distances with ease, are of comparatively small importance as evidence, 
although they have some value, while fresh-water shells, and, above all, 
fresh-water fishes, furnish testimony of the most value. The lung-fishes, 
Dipnoi, one of which is found in Australia, one in South America, and 
one in Africa, are usually brought forward as a case in point. It is ex- 
tremely improbable that such peculiar fishes could have originated in- 
1The fauna of a country is the sum total of its animal life, the flora, of its plant life, while the 
term biota embraces both, meaning the entire plant and animal life of any region or period. 
a 
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