The smaller kangaroos are called "wallabies," or brush kangaroos, and frequent scrub jungle and rocky places. These furnish most of the skins and leather sent to European markets and, like the big species of the plains, have been greatly reduced in numbers by hunters and sheep herders. Some of them are confined to the rough deserts and mountains, where they jump about the rocks with astonishing agility. One small genus includes the swift harelike species that resemble our jack rabbits in habits; and there are also the "dorca" kangaroos, which are arboreal in habit and handsomely colored. Another group are ratlike in form, colors, and manners, running rather than leaping, and dwelling among scrub and grass, scratching the ground all day in search of the roots upon which they feed, and making havoc in the frontiersman's potato patches. Several kinds have prehensile tails, which they use apparently only to carry to their underground homes the long grass of which they make their beds. They associate in connected burrows like a rabbit warren.
In the varied forms and functions they present, as beasts of prey, as grazers or root diggers, as ground-running, tree-climbing, burrowing or cave-haunting forms, some solitary and slow, others agile and gregarious, the marsupial tribe in its isolated corner of the earth exhibits an epitome of the whole mammalian world. It shows in a conspicuous way how the necessity and habit of making a living in varied circumstances, and exposed to lively competition, restricting every species to a particular manner, brings about a suitable modification of structure.
THE EDENTATA—ANTEATERS, SLOTHS, AND ARMADILLOS
At the base of the great division of Eutherian mammals, to which belong all that remain to be described, is found the order Edentata ("toothless"), whose modern representatives are few and unimportant in comparison with those of past ages, when gigantic ground sloths, armored glyptodons, and other fossil species flourished in a luxuriant world. The name is not well chosen, for many of these animals possess at least a few teeth, but always composed of vasodentine and not coated with enamel. Although the origin of this race is obscure, it was certainly far in the past, for its characters are archaic in many particulars, and its members are often far separated in structure, and also in their geographical distribution. Two families belong to the Old World, one in the Orient and another in South Africa, but all the other edentates are American. The Oriental one includes most of the "pangolins," or scaly anteaters, which are covered from head to foot in a coat of mail formed of overlapping horny plates, and can roll themselves into a ball that will defy any jaws not big enough to tear them to pieces; while the African family consists of the naked, long-nosed aard-vark ("ant bear"), which burrows in the ground, and cuts its way at night into the mud forts of termites and other ants in search of its favorite food. These two ancient creatures differ so much in their anatomy from the American edentates that they are classified by some naturalists in a separate order (Fodentia); and they differ almost as radically from one another.
It should not be surprising to find most of the modern edentates in South America, since that is the most ancient and unchanged of all the continents; but a few sorts of anteaters, sloths, and armadillos alone remain where once their race, in its heroic age, dominated the world of its time. The puny survivors look and act like the relics they are. The "great" anteater, or tamandua, standing eighteen inches or more in height, has flatfooted, bearlike hind feet, and short forelegs that end in huge claws bent under, or backward, so that the animal walks on the outer face of its toes. Its tail is a great bushy mass of hair with which the animal may cover itself as with a blanket, and its long neck tapers off into a head with a very long nose and little room for brains. The big claws are not used for burrowing an underground home, but for digging up the nests of ants and termites which it licks up with its long, sticky tongue. When one realizes the enormous colonies of ants in the tropics it is not amazing that so large an animal should subsist exclusively on these minute creatures. The claws are formidable weapons of defense also, the animal throwing itself on its back and defying the foe, or rising on its hind legs and giving a tearing, bearlike hug that even a man might well fear. This is a slow-moving creature, more fond of open country than forests; but a smaller tamandua belongs wholly to the woods and spends both days and nights in the tree tops, tearing open the burrows and nests of arboreal insects and devouring their inhabitants and their stores of honey and young. A third species is the rare little yellow two-toed anteater of the Isthmus region, which appears to live almost wholly on wasp grubs.
Much like these in organization are the two species of sloth, hairy creatures that hang all day long by their long, muscular limbs and two or three curved claws, underneath a branch of the tree through whose top they slowly creep about at night, collecting, crushing with their peglike teeth, and swallowing the leaves that constitute their fare. Their long hair, naturally gray, becomes green by accumulating a coating of minute plants that thrive on it, and this helps to conceal the sloths amid the foliage, yet they are killed by eagles and by all sorts of beasts of prey, against which they have no means of defense. These listless creatures are the degenerate descendants of a very long ancestry. The early Tertiary rocks of Argentina contain the bones of small slothlike animals that apparently were ground dwellers and must have been active diggers. Later that region became filled with larger ground sloths, apparently their descendants, that are believed to have browsed on bushes and trees; and some of these became the megatheres of the late Tertiary, which were as big as elephants. Similar giants inhabited North America.
Even in the earliest days known to paleontologists the anteater-sloth group had become well separated from their fellow edentates, the armadillos, arguing a far-preceding origin. In the later Tertiary the latter type developed such huge and heavily armored forms as the glyptodon, on whose bony shell the teeth of even the great saber-toothed tigers of the time could make little impression. These grotesque tortoiselike glyptodons, of which there was a great variety, were vegetable eaters, and some survived to a time so recent that there is evidence that they were finally killed off by human hunters. Beside them were smaller armadillos, more like the modern ones, which are armored with overlapping belts of horny material between which coarse hairs sprout; but the amount of this armor varies greatly among the several species scattered from Patagonia to northern Mexico. In some it is a continuous shell, in others it consists of several belts, in still others is nearly absent. Armadillos are carnivorous, digging out worms, grubs and the underground nests of wasps, catching insects of all sorts, stealing eggs and young from ground-nesting birds, killing serpents by leaping on them and sawing their bodies in two by means of the rough edges of their plates. In some places on the pampas armadillo burrows are so numerous as to make riding dangerous.