But here another question presents itself. How is it that these curious pouched animals have lived on in America as well as in Australia when they have been killed off in Europe and Asia? The answer to this is not far to seek if we remember that geology teaches us that there have been many changes of land and sea in past times, for the neck of land which joins South America to North America is very low and narrow, and a change of level of scarcely more than 2000 feet would break it up into islands; and as we know that such changes have taken place in past geological times, there is no doubt that once this neck was partially under the sea, and South America, like Australia, was a huge continental island, where the lower animals might struggle on and become settled, before the higher ones poured in to interfere with them.
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Indeed, if the opossums did not teach us this history, we might learn it from another singularly old-fashioned race of animals; for in the same Brazilian forests in which our little opossums are sporting, the dreamy Sloth, with his long arms, short legs with the knees bent outwards, and long thick hair drooping over his eyes, is hanging back downwards from the boughs; while the strange Ant-bear is tearing open the ant-hills with his strong bent claws in the damp earth below, and licking up the insects with his long sticky tongue; and the Armadillo, whose back is covered with bony shields like the crocodile, issues out of his burrow at night to dig for worms or roots or buried animals. We may look all the world over and we shall not find another group so strange and old-fashioned as this one, nor even any creatures of their kind, except the ant-eaters of the Cape and the scaly Manises of Africa and India, which also live, as you will notice, upon continents which jut out into the water, and not on the great northern mass of land.
Fig. 53.
South American pouched animal, the Opossum;[121] and imperfect-toothed animals—Sloth,[122] Ant-bear,[123] and Armadillo.[124]
In many ways these curious animals (Edentata) of South America and Africa are more singular, though not of so ancient a race, as the “pouch-bearers.” Many of them, the American ant-bears and the African Pangolins, are quite toothless, and those which like the sloth have teeth, have very imperfect ones more like the teeth of reptiles than those of marsupials; again, their feet have the toes much joined together, and the sloths have only three toes on the hind feet and sometimes two only on the front, and the joints of their neck are irregular in number. Thus we see in them that variability of structure which always points to a low order of animals; and, moreover, the armadilloes are the only milk-giving animals which are covered with bony plates like reptiles.
Fig. 54.
African imperfect-toothed animals—Aard-Vark or Cape Ant-eater in the background, and scaly Manis or Pangolin in the foreground.