EDENTATA, an order of Mammalia (q.v.) comprising the sloths, ant-eaters and armadillos restricted to the warmer parts of America. But this name, meaning toothless, applies only to the ant-eaters. The teeth of sloths and armadillos, however, are ab normal in being of persistent growth, seldom differentiated, with out enamel and invariably absent in the front of both jaws. A character distinctive of the order is the presence of accessory articular processes on some of the vertebrae. From this the name Xenarthra has been given to these groups to distinguish them from the pangolins and aard-varks of the Old World which were f or merly associated with the American edentates as Nomarthra on account of the normal construction of the vertebrae. There is, however, no evidence of kinship between the ant-eaters of the Old and New Worlds, such resemblances as they exhibit being super ficial adaptations to diet. The Pangolins and aardvark are there fore dealt with separately in this article.
The existing edentates are divided into two sub-orders, the Pilosa or Anicanodonta and the Loricata or Hicanodonta.
Pilosa.—In the Pilosa the anus and external genitalia are close together on a common eminence or enclosed in a fold of skin, both the clitoris and peris being quite short, and there is no exoskeleton of dermal bones. There are two well defined tribes, the Tardigrada or sloths and the Vermilingua or ant-eaters. In the Tardigrada the jaws are short, strong and the wide mouth is provided with teeth and a short flat tongue ; the tail is short or absent and the limbs are long and slender, the fore and hind feet are similar in being long and narrow and in having the two or three digits com pactly united and furnished with long, curved, equal claws. In the skull the zygomatic arch is branched.
The existing sloths feed upon leaves and are entirely arboreal. Their limbs are especially modified to enable them to climb or hang back downwards on branches, and their long coarse hair har bours microscopical green algae which serve to conceal them in the trees.
The sloths are referred to two families, the Bradypodidae and the Choloepidae. In the Bradypodidae, or three-toed sloths, all the feet are furnished with three digits, and the soles are almost en tirely hairy; there is a distinct tail; the hair on the head grows forwards, forming a frill round the face, the nostrils are small and the ears very simple. Sometimes known as ais, they are found in the tropical forests of South and Central America. The few known species are referred to two genera, Bradypus and Scaeopus.
The Choloepidae or two-toed sloths, also known as unau, have only two digits on the fore foot ; the soles are quite naked ; there is no external tail, the hair on the head grows backwards, the nostrils have a thickened margin and the ear is provided with a valvular flap. The single genus Choloepus, represented by a few species, ranges from Nicaragua to Brazil.
In the Vermilingua or ant-eaters the snout is elongated and down-curved, the mouth has a very short gape, a long worm-like tongue and no teeth; the fore and hind feet are dissimilar and the digits of the fore foot are unequal in size, the third being the largest and armed with a great falcate claw and the tail is very long. In the skull the jaws are weak and the zygomatic arch is slender and unbranched. The ant-eaters are assigned to two families, the Cyclopedidae and Myrmecophagidae.
In the Cyclopedidae, containing Cyclopes (Cycloturus) didaG tylus, the silky or two-toed ant-eater, the limbs are adapted essen tially for climbing. The f ore foot has only two digits with strong claws which close upon a large cushion-like pad, the hind foot has four fused digits, each with a long claw, and capable of folding down on to the heel for grasping ; the tail is prehensile and naked at the tip beneath but otherwise covered, like the head and body, with long silky hairs which on the head conceal the simple ears. The jaws and other parts of the skull are less specialized than in the next family. This little arboreal ant-eater, which is no bigger than a rat, is found in tropical South and Central America.
The Myrmecophagidae contain two very distinct forms, the great ant-eater (Myrmecophaga jubata) and lesser ant-eater or tamandua (Tamandua tetradactyla) . The feet are adapted for progression on the ground, although in the tamandua they also serve for climbing. The fore foot has four clawed toes, and on its outer side a large supporting pad; the hind foot has five toes, with short claws, and is plantigrade ; the hair is not silky and on the head is quite short so that the better developed ears are prominent. The skull differs from that of Cyclopes in having a weaker man dible and in the fusion of the pterygoids to prolong the narial pas sages. In the tamandua the tail is prehensile and covered mostly with small scales and short hairs, the hair of the body is short and smooth and the fore foot has a large carpal pad confluent with the ambulatory pad. This ant-eater, which is about the size of a cat, lives in the forests of tropical America.
The great ant-eater (Myrmecophaga jubata), standing over two feet high, is purely terrestrial in habits. The hair on the body and tail is long, shaggy and coarse, the tail is rigid and not pre hensile, the fore foot has a very large ambulatory pad and a small isolated carpal pad and the snout is much longer than in the tamandua. It lives in the swampy savannahs and forests of tropi cal America, feeding, like the other ant-eaters, mainly on termites, the nests of which it rips open with the great falcate claws of the f ore feet.
Loricata.—In the Loricata the external genitalia are long and not associated with the anus, as in the Pilosa; there is a dermal bony exoskeleton and the hairy covering is usually scanty. The Armadillos which constitute this sub-order are divisible into sev eral families.
In the Dasypodidae the bony exoskeleton consists of a head shield, one or more free bands on the neck, a large compact scapu lar shield encasing the fore quarters, followed by from 6 to 13 free dorsal bands and a large solid pelvic shield over the hind quarters, the scutes of these areas being tolerably alike in size and shape; the flexible tail tapers to a point and its bony rings never consist of more than two rows of scutes ; the skin of the lower surface is scantily hairy and tubercular ; the legs are scaly above and there are five toes on each foot, those of the fore foot being provided with fossorial claws, the fourth toe being the longest, while on the hind foot the third and fourth are subequal and all the claws are smaller ; the ears are large, situated on the sides of the head some distance behind the eye.
There are two subfamilies, the Dasypodinae and the Cabas soinae. The Dasypodinae have from six to eight dorsal bands, one neck band; the scutes are coarsely sculptured, and the tail has jointed rings. To this sub-family belong the six-banded ar madillo (Dasypus sexcinctus) of Paraguay and Brazil, and many related species. A remarkable Brazilian species (Scleropleura bruneti) has the dermal scutes defective, especially on the back. These armadillos are active animals of small or medium size, rang ing in length of head and body from about six inches in the pichi to a foot or rather more in the six-banded armadillo.
In the Cabassoinae there are from i 1 to 13 dorsal and from three to four neck bands, the scutes are often polished ; the scutes of the tail are not arranged in distinct rings and may be defective; and the fore feet are more fossorial, the claws of the third or third and fourth being specially enlarged. To this group belong the tatouay (Cabassous unicinctus) of Brazil and Surinam, and the giant armadillo (Priodontes gigas) of Brazil, which may reach a length of three feet.
To the family Tolypeutidae belong the apars or ball armadillos, so-called from their power to roll up into a compact sphere. In adaptation to this protective habit there is beneath the very large pelvic and scapular shields a deep recess into which the limbs can be withdrawn. The tail is very short and rigid. They also differ from the Dasypodidae in having from two to four dorsal bands and in being more digitigrade, the second, third and fourth toes of the hind foot, which have broad hoof-like claws, and the tips of the long claws of the third and fourth digits of the fore foot resting on the ground during progression. The toes vary from five to three. A few species of the genus Tolypeutes are admitted. The best known is the common three-banded armadillo (T. tricinctus) from the Argentine.
The little silky armadillo or pichiciago (Chlamyphorus trun catus), the type of the family Chlamyphoridae, differs from all existing armadillos in having a continuous series of scutes, forming transverse bands, extending from the head-shield to the pelvic shield, the latter forming a vertical semicircular disc giving a trun cated appearance to the hinder end of the body; in having the dorsal bands attached to the body along the middle of the back and overlapping its sides, which, like the ventral surface and legs, are clothed with silky hair, like a cloak; in the reduction of the ear to a tiny lobe close to the eye and in having the tail spatulate. The feet nearly resemble those of the Dasypodidae but have larger falcate claws. This armadillo, which is found in the sandy deserts of the Argentine, is an expert digger and largely subterranean in habits. A related genus, Burmeisteria, found in Bolivia, differs in having the shell adherent to the sides of the body and the bony scutes of the pelvic shield defective.
Taking first the Pilosa, the discovery of sloths and ant-eaters, differing but little from existing species, in Pleistocene deposits of South America, needs only passing reference. Of far greater interest are the ground sloths, the Gravigrada, standing between the Tardigrada and the Vermilingua, with skulls and teeth as in the former and the rest of the skeleton more as in the latter. The known genera are grouped round three main types Megatherium, Mylodon and Megalonyx.
Megatherium had a longish, very strong tail, broad hips and very stout hind limbs, with a huge heel and only three toes, the third alone being armed with a large claw; the fore limbs were long and strong, and four-toed, the second, third and fourth toes being armed with claws, that of the third being exceptionally large; there were well developed collar bones; the skull had anteriorly protruding massive jaws, with a thick, branched zygomatic arch. There is no doubt that this great beast, measuring 18 ft. long, the skull being about two feet, fed upon foliage and twigs which he reached by rearing up against a tree trunk, supported on his hind legs and tail, and using his fore legs to pull down the branches, and a long flexible tongue to gather the leaves into his mouth. It also seems clear that in standing and walking on the ground he rested on the outer side of both fore and hind feet. The remains of Megatherium itself are found in Pleistocene deposits of the southern United States and South America. Related forms occur in the Pliocene of Argentina, and considerably smaller forms, regarded as ancestral, occur in Miocene beds of Patagonia.
Mylodon, although smaller, with the skull about a foot and a half long, closely resembled Megatherium in general form, but had weaker, short jaws, differently shaped, smaller teeth, and five toes on the fore foot and four on the hind, but evidently walked on the outer side of both feet, like Megatherium. Its re mains are found in Pleistocene beds of North and South America. There are many related genera, also Pleistocene. Of particular in terest was Glossotherium on account of the presence of bones in the skin beneath the hair, recalling the exoskeleton of the arma dillos. Supposedly ancestral forms of Mylodon and its allies are found in Miocene deposits of Patagonia.
Megalonyx, with the skull a foot or more in length, found in Pleistocene and Pliocene deposits of North America, is distin guished from the preceding genera by having the first of the five upper teeth large, tusk-like and isolated. A large number of re lated genera from Miocene deposits in Patagonia are smaller and less specialized.
It is amongst the earlier Miocene forms of Gravigrada that we find evidence of convergence between the sloths and ant-eaters. Not only are they smaller than the later evolved forms but their limbs are more slender and their feet more normal, in the number and size of the digits, and in the hind feet being plantigrade, as in the great ant-eater.
With regard to the Loricata, many existing genera occur in the Pleistocene of Argentina and Brazil; and Pleistocene and Pliocene beds have yielded remains of a huge armadillo (Chlamydothe rium), comparable to a rhinoceros in size and with teeth less sim plified than in surviving species. A large number of genera ap proximating to existing forms have also been found in Miocene and earlier deposits in Patagonia. One of these, Stegotherium, is of particular moment from possessing long, narrow jaws with a few minute, simple teeth at the back of the mouth, thus approach ing the long-jawed toothless ant-eaters. But excelling all in in terest are the Glyptodonta, a tribe of extinct, highly specialized armadillos distinguished by having the entire body encased in an unjointed bony cuirass, in the fusion of the vertebrae of the back, the peculiar jointing of the neck so that the head could be withdrawn into the shell, and in the structure of the skull which was remarkably like that of Megatherium, in general appearance. To support the great weight of the cuirass the feet were short and broad with hoof-like nails especially on the hind feet ; and the long tapering tail was jointed, with bony rings in its basal por tion and encased in an unjointed sheath at the end. Some of these armadillos, like Glyptodon and Panochthus, from the Pleistocene of South America, were eight or nine feet long and about four feet high and they moved, about slowly, grazing on herbage like huge tortoises. They died out in the Pleistocene ; but the group is traceable through the Pliocene back to Miocene deposits of Patagonia.
Another group of extinct mammals, shown by the structure of their vertebrae to belong to the edentate stock, is the Taeniodonta or Ganodonta whose remains occur in Lower and Middle Eocene deposits in North America. In the structure of the skull and of the massive limbs this sub-order shows considerable resemblance to the Gravigrada; but although the median incisor teeth, both above and below, seem to be missing, the rest of the dentition is quite unlike that of typical edentates in being heterodont, with large canines and cusped, usually rooted cheek-teeth, all more or less covered with enamel. The best known forms are Conoryctes, Psittacotheriusn and Hemiganus.
The Lower Eocene of North America has yielded yet another group, the Palaeonodonta (Palaeonodon, Metachiromys), which has been claimed to be ancestral to the edentates. It is said to resemble the Loricata in the structure of the feet and other respects, such as the absence of incisor teeth, but differed in the absence of dermal bones and of cheek-teeth and the presence of large cutting canines. Since, moreover, the vertebrae were normally constructed and there was no union between the poste rior part of the pelvis and the anterior vertebrae of the tail such as is found in all typical Edentata, it is difficult to justify this clas sification.