THE PIONEERS OF THE ARMY OF MAMMALS
CHAPTER IX.
FROM THE LOWER AND SMALLER MILK-GIVERS WHICH FIND SAFETY IN CONCEALMENT, TO THE INTELLIGENT APES AND MONKEYS.
Having now taken leave of the curious pouch-bearers and the strange primitive sloths and armadilloes, we find ourselves left to deal with an immense multitude of modern mammalia, which have spread in endless variety over the earth, and which may be divided into five great groups—the Insectivora or insect-eaters; the Rodents or gnawers; the climbing and fruit-eating Lemurs and Monkeys; the Herbivora or large vegetable-feeding animals; and the Carnivora or flesh-eaters.
All these groups are very distinct now, and we naturally turn back to ancient times to ask how they first started each upon their own road. But when we do this, we meet with a history so strange that it makes us long to open the great book of Nature still further, and by ransacking the crust of the earth in all countries to try and find the explanation, which will no doubt come some day to patient explorers. The history is this. We saw in the last chapter that in those far distant ages, when even reptiles were only beginning to spread and multiply by land and sea, and when, although birds probably existed, still they did not as yet leave any traces behind, small milk-giving and insect-eating animals, the Microlestes and Dromatherium (see [p. 183]), were already living upon the earth, and left their teeth and jaws in the ground.
Now, as ages passed on and the reptiles increased in strength, these little milk-giving animals evidently flourished, for though we have not yet discovered any of their bones in the rocks of the Chalk Period, yet as we find them both before and after that time, they must have lived on in some part of the world, the rich vegetation and abundant insect life affording them plenty of food. Meanwhile the huge reptiles, of kinds now long extinct, reigned over land and sea and air, and were in the height of their glory,—when suddenly there comes a blank and their history ends. When we look again, “a change has come o’er the spirit of the dream,” and in the next period we find their bones no more. From that time we meet only with the four groups of lizards, snakes, tortoises, and crocodiles, which still survive; and the place of the swimming, flying, and walking reptiles is taken by four-footed and milk-giving animals.
Some of these were still marsupials like those that had gone before; others were of strange forms, distantly related to them; others were curious ancestral forms of our hyænas and bears, dogs and civets, horses and tapirs,[129] in which the characters which distinguish these groups were not so distinct as they are now, while others again were old forms of moles, hedgehogs, squirrels, bats, and lemurs. In what part of the world, then, had all these been growing up, that we come upon them so suddenly? Before the seas of the chalk only the small marsupials; after them, when the areas of land began to increase in extent, a whole army of milk-givers, so different from each other and so well adapted for their lives, that we even find among them such peculiar forms as whales, with their arms converted into paddles, and bats with their arms acting as wings.
What an idea this gives us of the immense period of time that must have elapsed while the chalk was forming, the reptiles becoming extinct, and the mammalia taking their place!
We have had a hint of this before, when we learned in Life and her Children how infinitely minute the shells are of which chalk is made, and what enormous thicknesses remain of the chalk-beds. And now we find these facts strengthened by the great changes which then took place in the animal world, for even if (as is likely) older forms of these large milk-givers existed in earlier times, and we have not yet found them, yet there are such great differences between whales, bats, dogs, and lemurs, that our imagination stands appalled at the time required to account for them.
Again, where are the traces of all the forms which must have existed between the little marsupials and this great army of four-footed beasts? At present no one can answer. Forty years ago we knew nothing even of those early marsupials, and people said there were no milk-giving animals until after the time when the chalk was formed. Now a few jaws have told us that milk-givers had been already in the world for ages; and it may be that before forty years more have passed, some child now reading these lines, and following in the footsteps of such patient explorers as Beckles and Gaudry, or the American naturalists Leidy, Cope, Marsh and others, who have such a grand field before them, may discover bones which will unravel the history of that crowd of mammalia which now seems to start up like Cadmus’ army from the ground.
But for the present we can only begin with them as we find them immediately after the Chalk Period, and a strange motley group they appear. There, roaming among the palms, evergreens, screw-pines and tree-ferns, which flourished in Europe and North America in those warmer times, were beasts larger than oxen, with teeth partly like the tapir, partly like the bear, and feet like the elephant,[130] which may have been both animal and vegetable feeders. With them were true vegetarians, which could be called neither rhinoceroses, horses, nor tapirs, but had some likeness to each.[131] Others, half-pigs half-antelopes, were thick-skinned, but graceful and two-toed,[132] while a little fellow no bigger than a fox,[133] with five toes on his front feet and three behind, the ancestor of our horses, grazed in the open plains. There too, moles, hedgehogs, and dormice had already begun to make their underground homes, and squirrels and lemurs sprang about the trees of the forest, where bats roamed at night in search of insects. Nor was this life without its dangers, for beasts of prey, half-bears half-hyænas,[134] were there to feed upon their neighbours, and with them a creature half-dog half-civet,[135] with several other carnivorous animals with feeble brains and partly marsupial characters,[136] and lastly a large flat-footed dog-bear,[137] something between a dog, a cat, and a bear, with a very small brain but plenty of teeth, represented the most primitive flesh-eating animal known to us.