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.
[CHAPTER XXVIII]
THE GNAWERS
The great order Rodentia—rats, mice, rabbits, porcupines, squirrels, beavers, etc., derives its name from the Latin verb rodere, to gnaw, or eat away (something), and is characterized by the great development of the front (incisor) teeth, by means of which rodents get their living by biting off, or gnawing through, the plants and woody stems on which they feed, or which they use in constructing their dwellings. All are primarily vegetable eaters, yet none will refuse a meal of flesh when opportunity offers to get it, and some are decidedly carnivorous, especially as to fish. They are distributed all over the world, including the Australian region. They are chiefly terrestrial, and often burrow or live in ready-made burrows. Some are aquatic, such as the voles; others, like the squirrels, are arboreal. In perhaps a majority of the forms the hind legs are much longer and stronger than the forelegs, giving the animals great leaping power, while the forefeet, with their long and flexible fingers, are constantly used as hands. Many are beautifully marked in varied tints of gray, brown, red, and black, so that their pelts have value in the fur market; and their flesh is an important element in human food. On the other hand the activity of these animals, when numerous, causes serious damage to gardens, crops and orchards and one of them, the rat, is unquestionably the most dangerous animal to human health and prosperity in the whole animal kingdom. The fecundity of the smaller, murine species, is great, and from time to time they increase inordinately in favorable places, and swarm abroad in vast and destructive migrations. Were it not for the fact that the rodents furnish the principal part of the food of predatory mammals, reptiles, and birds, and are thus kept down, the globe would soon become so populous with this tribe that hardly anything else could maintain existence.
The distinguishing anatomical characteristic of the rodents is the dentition. The canines, so essential to carnivorous, predatory animals, are here completely absent, and a long empty space intervenes between the incisors and the molars, or cheek teeth, which vary greatly in number and form among the different families. The incisors consist of a single pair in each jaw, very large and strong, and composed of vasodentine, faced only with hard enamel, often yellow or red. As the softer substance behind the facing wears away more easily, the incisor takes a chisel shape, leaving the hard enamel in front projecting slightly as a cutting edge; thus these teeth always remain sharp. The rodents are traced back in their lineage to the order Tillodontia of Eocene time. The oldest family of modern type in the order is that of the squirrels.
Let us begin with the rabbits and hares (family Leporidæ). The name properly applies to the Old World species Lepus cuniculus, the burrowing wild rabbit from which all our various domestic rabbits are descended, whose special characteristic is the fact that they live in holes in the ground of their own digging, and in large colonies called warrens. All the other species make their breeding beds and resting places on the surface of the ground, in the best concealment (outside of forests) that they can find. Such a home is called the animal's "form," and when it contains a litter of young the mother covers them with a blanket of hair which at that season she is shedding copiously. Strictly speaking, all the Leporidæ, except the cuniculus, are "hares"; but the general term "rabbit" is now so common that the scientific distinction is of no consequence. Europe and Asia have two kinds of hares, and several exist in this country, such as the familiar "cottontail" or bush rabbit of the east, the southern swamp rabbit, and several species of large, long-eared, swift-footed hares of the western plains called "jack rabbits." The most important one, however, is the large northern one named "snowshoe rabbit," because in winter it receives a broad growth of hair on the feet, aiding it in traveling over the snow. This rabbit turns white in winter, the hairs losing their color with the advent of cold, as also does the big arctic hare which wanders as far north as land extends. These northern hares are the chief dependence for food in winter of all the Canadian fur-bearing animals, and indirectly of the native Indians. Consequently when, as happens at intervals of a few years, the rabbits of a district all but wholly die off by an epidemic, a famine and dreadful distress occurs—or used to when civilized aid was less available than now—in northern Canada, and the commercial outcome of furs is greatly diminished.
As the hares feed on herbage and bark, obtainable all the year round, they are abroad in winter; but they have a family of small cousins, the pikas (Lagomyidæ) that inhabit our western mountain tops above timber line and must hibernate. Other species abound in the Himalayas. They are little, short-eared, tailless creatures that make their homes in companies among loose rocks, and store in their deep crevices enough dried grass and flowering plants to keep themselves alive until the late spring of those cold heights. Western folks call them conies.
The porcupines are large, plantigrade rodents notable for the mixture of quill-like spines with the hair. This is most conspicuous in the European species, which bristles with spines reaching far beyond the hips and concealing the tail, forming an excellent defensive armor. Some smaller African and East Indian species are less well armed, and have longer tails, at the end of which are tufts of spines, making an effective weapon. All of these pass their time and get their food on the ground. Our American porcupines (family Cercolabidæ) differ somewhat anatomically and live for the most part in trees, although our common eastern porcupine wanders about a great deal in summer, especially at night, feeding on herbage, and rejoicing in a find of bones or other saline food here and there. It is defended by a coat of long black hair in which spines are plentifully mingled, and the short, flat tail, covered with thick spines, may give a sidewise stroke that makes man or beast cautious about attacking an animal that otherwise seems so lethargic and helpless. The porcupines of this family, however, really belong to trees, where they slowly consume the foliage and tender bark, and remain quietly through even Canadian winters. The Pacific side of the country has a similar species in the yellow-haired porcupine; and several smaller kinds exist in Central and South America with scanty spines and long prehensile tails.
Closely allied to the porcupines are the gregarious viscachas of the South American plains, that live in "villages" of burrows, and much resemble prairie dogs in appearance and habits; also the chinchillas of the high levels of the Andes, whose soft gray coat is one of the prizes of the furrier. Here, too, come the swift-footed, slender agoutis and pacas of South America, many species of which exist and are useful as food; and a neighboring family contains the little cavies, from one of which are derived our pet "guinea pigs," which are not pigs and do not come from Guinea; also their cousin, the almost aquatic capybara, which measures three feet long, and so is the biggest known rodent. This is much hunted for its flesh, and is the principal prey of the jaguar.
This brings us to the world-wide tribe of rats and mice formed by a group of eight families, of which the typical one (Muridæ) alone contains a third of all Rodentia, and the other seven creatures differing greatly from these familiar models. Many are small, such as the house mouse (originally a native of southeastern Asia, as also were the rats that commerce has carried all over the civilized globe), and the even tinier harvest mice, gray or brown in plain color, and with long, slender and nearly hairless tails and legs fairly equal in size. Thence in size they grade up to the stature of the rat, and from that on to the South African "springhaas" which is as big as a rabbit, and to our muskrat, two feet long, counting in its tail. Although essentially alike in structure some have varied widely from the ordinary type. Thus the jerboas, several species of which inhabit the plains of Asia and Africa, have the hind legs so long that their bones are considerably longer than the distance from the root of the tail to the nose; and they progress in long rapid leaps, balancing themselves by long tails, often tufted at the end. The big "jumping hare" of South Africa has much the appearance of a kangaroo with a squirrellike tail; and a genus of exquisitely dressed mice in our sandy Southwest are called "kangaroo" mice. In fact one of our commonest reddish field mice, found all over the country, has similar proportions, and is remarkable for its long leaps when hurried.
A shortening of the tail is seen in the voles, to which the common meadow mice of various species belong, and still more in the lemmings, in the Old World mole rats, and in our pouched gophers. All these are not only ground-keeping kinds, but burrowers, and have no use for a long tail, save in the case of the muskrat, which is really a big vole that has taken to an aquatic life, and needs an oar to scull himself through the water; for muskrats swim more by means of their tails than by their feet. The foremost burrowers are the pouched gophers, whose long tunnels, and food-getting, do so much damage to crops in the central plains region of this country. They must be distinguished from the ground squirrels, also called "gophers."
An interesting diversity of habits may be met with here. Some rodents live in deeply excavated burrows, others in shallow diggings or holes in stumps and rock crevices; some, like the water voles, reside in holes in the banks of streams, or, like the muskrat, heap up "houses" in a marsh in which to pass the winter in security; while still others construct ball-like nests among the herbage, or in bushes and trees. Some truly hibernate in cold countries, like the famous dormice of Europe, and our equally sound sleeper, the American jumping mouse; but mostly they stay in snug habitations and live through the winter on collections of food, or, like field mice, gather seeds abroad even in the coldest weather, or poke about under the snow for food, as do the lemmings. From time to time certain species, especially of the short-tailed field mice and the lemmings, multiply excessively in some district, and then are forced to spread away from their birthplace in those migrations of myriads which form the "plagues" that devastate large tracts of country. They march on until an accumulation of enemies and an epidemic of illness combine to kill them off.