As here employed, excluding the so-called edentates of the Old World, the Edentata form a highly variegated, but natural, assemblage of related forms. The order is at present exclusively American and almost confined to the Neotropical region, an armadillo which extends into Texas being the sole exception. These animals are so peculiar and so isolated from other mammals, that it has been proposed to treat them as a separate subclass; and there is much to be said in favour of this procedure, though it would perhaps be premature, until more is learned concerning these most curious and exceptional animals. In the subjoined table only the more important and better known genera are included.

In the section Pilosa, which includes the sloths (Tardigrada), anteaters (Vermilingua) and the extinct †ground-sloths (†Gravigrada), the skin is thickly clothed with long hair, and in the Loricata, armadillos and †glyptodonts, the head, body, tail and legs are more or less completely encased in an armour of bony scutes covered with plates of horn, but with some hairs also.

The name Edentata (toothless) is not very happily chosen, for only the anteaters are quite toothless. Almost all the genera have no teeth in the front of the mouth and the teeth are nearly always alike, so that the distinction of regions among them is entirely a matter of position in the jaws. In the tree-sloths and many †ground-sloths the foremost tooth in each jaw is a more or less enlarged, canine-like tusk. The teeth are always rootless, growing from permanent pulps, and are without enamel, made up of dentine, which is sometimes homogeneous and sometimes in layers of different hardness, and with a covering of cement, usually thin and film-like. The number of teeth varies from 4/4 to 10/10 or more, and their form usually approximates a simple cylinder, worn off flat at the end, though the ends may be bevelled or grooved, differences which are in no way due to pattern but simply to the mode of wear. In the †glyptodonts the teeth were divided by deep vertical grooves into two or three pillars, connected by narrow necks. In most of the edentates there is no change of teeth, the milk-dentition having been completely suppressed, but in the 9-Banded Armadillo (Tatu) each of the permanent teeth is preceded by a two-rooted milk-tooth, and some other armadillos have milk-teeth.

The skull varies much in form and proportions, according to the character of the food and method of feeding. The tree-sloths and †ground-sloths have short, rounded heads; in the †glyptodonts, the skull was short and remarkably deep vertically; while the armadillos have long, shallow heads, with tapering muzzle, the length and slenderness of which differ in the various genera. In the anteaters the skull is extraordinarily elongate and slender. The sagittal crest is seldom present at all and never prominent. The zygomatic arch may be complete or interrupted; in the tree-sloths, †ground-sloths, †glyptodonts and some extinct armadillos, there is a descending, plate-like process given off beneath the eye.

The backbone displays some of the most remarkable peculiarities of the order. The neck in the tree-sloths has eight or nine vertebræ, the only instances known among mammals in which the normal number of seven is departed from. In the armadillos and †glyptodonts several of the neck-vertebræ are coössified into a single piece, but the atlas is always free, so as to permit the movements of the head. In the posterior part of the dorsal and in the lumbar region the articulations between the successive vertebræ are by far the most complex and intricate known among mammals; in the tree-sloths these have degenerated, though still plainly indicated. In the †glyptodonts, which were covered with a huge, tortoise-like carapace, mobility of the backbone was needless, and so all of the dorsal vertebræ were united into one long piece and the lumbars were coössified with one another and with the sacrum. The sacrum consists, throughout the order, of a very large number of vertebræ and is attached to the hip-bones at two different points, instead of only one, as in other mammals. The tail varies much in length and thickness; in the tree-sloths it is extremely short and in the anteaters very long and bushy, prehensile in the arboreal members of the group; in the †ground-sloths, especially the gigantic forms, it was of immense thickness; while in most of the †glyptodonts a varying number of the terminal vertebræ were fused together. The sternal ribs are better developed than in any other mammals, and in the anteaters and †ground-sloths they articulate with the breast-bone by regular synovial joints, and each rib has head and tubercle like a vertebral rib.

In the limbs and feet there is great variety, according to the manner of their employment. The shoulder-blade has a very long acromion and very large coracoid, which long remains separate from the scapula; collar-bones are very generally present, though often in much reduced condition. The hip-bones have in the tree-sloths, †ground-sloths and †glyptodonts a much expanded anterior element, which in the other groups is narrow. The humerus usually has very prominent deltoid and supinator ridges and epicondylar foramen; the fore-arm bones are always separate, and there is generally much freedom of rotation of the manus. In the wrist there is no distinct central and usually there are the ordinary eight separate bones. The tibia and fibula are frequently coössified. The tree-sloths, which lead most strictly arboreal lives and are almost helpless on the ground, are unique among mammals in that the body is habitually suspended from the limbs, not carried upon them; the feet are curved hooks, which fit over the tree-branches and support the weight without muscular exertion. The limb-bones are very long and slender, the claws long, curved and sharp, and the metapodials of each foot, two or three in number, are fused into a single mass. In the †ground-sloths there was much change in foot-structure during the course of their recorded development; they were usually five-toed and the feet were armed with one or more great claws; the later and larger representatives of the suborder walked upon the outer edge of the feet.

The armadillos, which are largely burrowers, have five-toed feet and long, heavy, pointed claws, but in some of them the pes has a varying number of flat, hoof-like nails. The immense †glyptodonts had very short, broad feet, shod with hoofs, which, in some of the genera, were longer and more claw-like in the manus.

The recorded history of the edentates was developed almost entirely in South America. In the Casa Mayor formation there were numerous armadillos, but as only scutes of the carapace have been found, little is known of them. The †ground-sloths (†Protobradys) have been reported, but from such imperfect material that the reference is uncertain. The first assuredly determinable members of this suborder were in the Astraponotus beds and, associated with them, the most ancient known †glyptodonts. In the Deseado stage were many armadillos, some of them extremely peculiar, several †glyptodonts and †ground-sloths, some species of the latter very large. Edentates were far more numerous and varied in the Santa Cruz than in any of the preceding stages. Tree-sloths and anteaters have both been reported, but the evidence is insufficient, though there can be little doubt that these suborders had begun their separate existence in some part of South America other than Patagonia. The three families of †ground-sloths were already distinguishable, though much less clearly separated than they afterwards became; none of them were large animals, smaller even than some of the Deseado species and veritable pygmies in comparison with the giants of the Pliocene and Pleistocene. The †glyptodonts were likewise far smaller than their Pliocene and Pleistocene successors and in several respects more primitive, approximating the armadillos more closely; nor was there any such variety of forms as in the later stages. The armadillos were extremely numerous and varied; they all belonged to extinct genera and most of them apparently have no descendants at the present day. The tropical forests of Brazil and the Guianas must then, as now, have swarmed with mammals which did not extend their range to Patagonia and of which we consequently have no record. No doubt, it was in these forests that the ancestors of most modern armadillos, as well as of the tree-sloths and anteaters, lived in Miocene times.

Pliocene edentates were of the same suborders as those of the Santa Cruz, but far larger in size. Most of them are known only from very incomplete specimens, but the Pleistocene has yielded an enormous mass of beautifully preserved material. Of the tree-sloths and anteaters, only questionable remains have been found. That these tropical and forest-loving animals should not have occurred in the open Pampas of Argentina is not surprising, but it is difficult to account for their absence from the extremely rich cave-faunas of Brazil. Nearly all the existing genera of armadillos have been obtained, and with these were associated several extinct genera, some of them (†Chlamydotherium, †Eutatus) relatively huge, as large as tapirs. There was a wonderful variety of †glyptodonts, most of them enormous creatures, of which no less than five genera have been collected in Argentina and Brazil, and the †ground-sloths were even more numerous and varied. Nine genera, with many species, of these great beasts, which ranged in size from an elephant to a tapir, are already known and no doubt the list is still incomplete. These †glyptodonts and †ground-sloths must have been among the most conspicuous elements of the Pleistocene fauna.

Aside from certain problematical Eocene forms, the first North American edentates, which were immigrants from the southern continent, appeared probably in the middle Miocene of Oregon in the form of †ground-sloths, but the specimen, as well as a similar one from the lower Pliocene of Nebraska, is not sufficiently complete for positive reference. In the middle Pliocene the †ground-sloths and †glyptodonts were unquestionably present, and in the Pleistocene these two suborders were numerously and conspicuously represented. Three or four genera of the huge, elephantine †ground-sloths coexisted in Pleistocene North America. †Megalonyx was abundant in the forested regions east of the Mississippi, from Pennsylvania southward, and on the Pacific coast; †Mylodon was transcontinental in distribution; while †Megatherium was apparently confined to the southern states. While all three genera undoubtedly originated in South America, †Megalonyx has not yet been found in that continent.

This genus was originally named by President Jefferson in 1805 from an ungual phalanx found in a cave in Virginia, and he imagined that it belonged to a colossal lion which must still be living in the mountains of western Virginia. This was deduced from the assumption that no species could become extinct, and the passage is of interest as showing the prevalent belief of the time, although Cuvier had already demonstrated that many species had actually been extinguished. The passage is as follows: “The movements of nature are in a never ending circle. The animal species which has once been put into a train of motion is still probably moving in that train. For, if one link in nature’s chain might be lost, another and another might be lost, till this whole system of things should evanish by piecemeal.”

The †glyptodonts were also southern in distribution, and only very imperfect remains of them have yet been recovered from the North American Pleistocene, quite sufficient, however, to make the identification certain.

There were several genera of rather small †ground-sloths in the Pleistocene of Cuba. The best known of these, †Megalocnus, had several peculiarities of structure, but was plainly a member of the †Megalonychidæ. The ancestors of this genus probably invaded Cuba in the Pliocene, when the island was joined to Central America.

Suborder †Gravigrada. †Ground-sloths

As the †ground-sloths would appear to have had a more central position within the order than any of the other groups, our study of development may well begin with them. In the Pleistocene there were three families of these gigantic brutes, which ranged through the western hemisphere from Pennsylvania and California to Patagonia. Unfortunately our knowledge of the developmental stages within the different families is very unequal, and it is therefore impracticable to do more than sketch the changes of the suborder as a whole and in a general way. In the successive geological stages the proportionate representation of the different phyla varied greatly; in the South American Pliocene and Pleistocene the †Mylodontidæ and †Megatheriidæ were the abundant forms, while the †Megalonychidæ were but scantily represented. In the Santa Cruz Miocene, on the other hand, the overwhelming preponderance was with the †Megalonychidæ, the other two families being comparatively rare and incompletely known. From the still more ancient formations, the material so far collected is so fragmentary that family distinctions have little meaning. After all, there was no very wide range of variation among the contemporary members of the three families, and the differences were principally in size, in the form and number of the teeth, the shape of the skull and the number of digits; in essentials they were all much alike.

The genus †Megatherium (Fig. 122, p. 220) included the largest and most massive members of the suborder, †M. americanum being as large as an elephant, but very differently proportioned, as it was much longer and lower in stature, owing to the shortness of the extraordinarily heavy limbs; some of the skeletons measure 20 feet or more in length. The teeth, which were 5/4 in number, formed an uninterrupted series on each side; all had the same quadrate form and by abrasion were worn into two transverse ridges, formed by the meeting of the harder dentine with the thick coating of cement. The result was a form of tooth which much resembled the lower molars of a tapir, but it was not a tooth-pattern in any proper sense of the word, being due entirely to the mode of wear.

The skull was very small in proportion to the huge body and was low and narrow in shape; the cranium had a broad, flat roof, without sagittal crest; the orbit was completely encircled in bone, and the descending process of the zygomatic arch beneath the eye was very long and conspicuous. The nasals were short, and the slender, toothless premaxillaries projected far in front of them, which makes the presence of some sort of a proboscis likely. The lower jaw had a long, narrow, spout-like symphysis, which was abruptly rounded at the free end, not pointed; below the teeth, the lower margin of the jaw was very strongly convex, descending in a great flange. The neck was short, the body very long and enormously heavy, as was also the tail. The immense shoulder-blade had a very long acromion, which curved forward and inward, fusing with the coracoid and forming a bony loop or bridge. The hip-bones had the anterior element (ilium) enormously expanded transversely, so as to support the huge mass of viscera in the semi-erect position which the animal, it is believed, frequently assumed in feeding. Collar-bones were present.

The fore limb was very much more slender than the hind, but of nearly the same length. The humerus had a comparatively slender upper portion and extremely broad lower end, due to the great development of the internal epicondyle and supinator ridge; there was no epicondylar foramen. The radius evidently had the power of very free rotation upon the humerus. The femur was short, flattened antero-posteriorly, but excessively broad and heavy, and had no third trochanter. The tibia and fibula were likewise short and very massive and were extensively coössified at each end, leaving but a short interspace open between the bones. The very peculiar feet were so connected with the limb-bones, that the animal must have walked upon the outer edge of the foot, somewhat as the existing Ant-Bear (Myrmecophaga jubata) uses the fore foot. The manus had four functional digits, the first being a mere vestige; the fifth, upon which the weight rested in walking, had two very small phalanges and no claw, while the second, third and fourth had long, sharp claws. The pes had but three functional digits, for the first and second were reduced to rudiments; digit III had an enormous claw and of this digit the metatarsal was short and very heavy and the first two phalanges were fused together; the two external digits, Nos. IV and V, had no claws. The astragalus had a very peculiar shape, made necessary by the application of the external border of the foot to the ground and thus in both fore and hind feet the great claws were turned inward and, in the case of the pes, it must have been impossible to rest the sole upon the ground. The heel-bone was enormous and club-shaped and formed the hinder portion of the weight-carrying outer edge of the foot.

Almost all who have studied the structure of this extraordinary beast are agreed as to its habits. That it fed principally, if not exclusively, upon leaves, is indicated by the teeth. The general opinion as to its manner of life is well summed up by von Zittel: “The hip-bones, hind legs and tail are characterized by enormous strength. The entire structure of the extremities proves that the gigantic sloth could move over the ground but slowly and clumsily; on the other hand, the fore limbs served as grasping organs and were presumably employed to bend down and break off twigs and branches and even to uproot whole trees, while the weight of the body was supported upon the hind legs and tail.”[19] It would be quite absurd to suppose that such ponderous animals could have been climbers or burrowers, hence the function of the enormous claws, especially the single one of the pes, is not obvious, though they may have been merely the weapons of the otherwise defenceless monsters. The great claw in the fore foot of the Ant-Bear is a terrible weapon, with which the creature vigorously and successfully defends itself against dogs, and it may even be dangerous to men, if incautiously molested.

†Megatherium had no bony scutes, or other ossifications in the skin, so far as is known, and was probably covered with long and coarse hair, as is known to have been the case in another †ground-sloth.

Less specialized in many respects than the †megatheres was †Mylodon, type of a family which was numerously and variously represented in the Pleistocene of South America, much less so in that of North America. †Mylodon was smaller and lighter, being from ⅓ to ¼ smaller in linear dimensions than †Megatherium, and the contemporary †Scelidotherium was no bigger than a tapir. The teeth numbered 5/4 and the anterior one above and below had a somewhat tusk-like form; the others were worn off evenly, with nearly horizontal grinding surface, but a vertical groove on the inner side gave them a subtriangular, lobate form. The skull was short and broad, with flat top, and orbit only partially enclosed behind; the premaxillaries were very short and the muzzle very broad and abruptly truncated, the nasal opening very large. The lower jaw had a straight inferior border, a short, very wide and shovel-shaped symphysis and square chin. Nothing indicates a proboscis, and the head must have been very different from that of †Megatherium.

Within the family of the †mylodonts there was some variety in the dentition and more in the shape of the skull. In †Lestodon, for example, the first tooth in each jaw was a large, sharp-pointed tusk, the muzzle was greatly broadened, and the whole animal was larger. †Scelidotherium, the smallest Pleistocene member of the family, had a much narrower and more elongate skull than the others. In †Glossotherium, which also had an elongate skull, there was an arched bony bridge connecting the anterior end of the nasal bones with the premaxillaries and dividing the nasal opening into two parts.

The neck, body and tail of †Mylodon did not differ materially from those of †Megatherium, except in being smaller and less massive. The fore limb was relatively somewhat shorter and much stouter, but otherwise similar; the humerus had no epicondylar foramen and the femur no third trochanter; the tibia and fibula were separate. The manus had five digits, Nos. I, II and III carrying claws, that of III being especially large; IV and V had no claws and the outer edge of the manus rested on the ground in walking, the sole turned inward. The pes had lost the first digit, the second and third had claws, but not the fourth and fifth; the weight rested on the outer edge.

The skin is definitely known from large pieces belonging to the allied genus †Grypotherium, found in a cavern near Last Hope Inlet, Patagonia, where it had been preserved by burial in dry dust. Externally, the skin was thickly covered with coarse hair and in the deeper layers was a continuous armour of small ossicles, which were close set and in the Last Hope specimens show like a cobble-stone pavement on the inner side of the skin, the innermost layers of which have been destroyed; in life, these small bones were not visible. Similar ossicles have been found in association with several skeletons of †Mylodon. The habits, diet and mode of feeding of the latter were no doubt essentially similar to those of †Megatherium, but †Scelidotherium, which had a much shorter and lighter tail, was probably more quadrupedal and browsed upon low shrubbery.

The third family, the †Megalonychidæ, was scantily represented in the Pleistocene of South America, but relatively common in North America. †Megalonyx was, on the whole, less specialized than †Mylodon or †Megatherium, but had a strong resemblance to both of them. The teeth, 5/4 in number, had the foremost one in each jaw separated by a considerable space from the others and more or less tusk-like in form; the grinding teeth were worn smooth, without ridges, and of somewhat trihedral shape. The skull was short, broad and deep, resembling in shape that of the tree-sloths; there was a long, but feebly developed sagittal crest, and the orbits were widely open behind, with hardly a trace of any posterior boundary. The muzzle was very short and broad and abruptly truncated and the premaxillary bones were extremely small. The lower jaw was short, thick and massive, with very broad symphysis and almost vertical chin. Neck, body, tail, shoulder and hip-bones did not differ sufficiently from those of †Megatherium to require particular notice.

The fore limb was shorter and more slender than the hind; the humerus had the epicondylar foramen and the very massive femur retained the third trochanter; the tibia and fibula were separate. The feet had five digits, three of which carried claws; the calcaneum was very peculiar, not at all like the massive, club-shaped bone of †Megatherium and †Mylodon, but long, comparatively thin and sickle-shaped. Nothing in the skeleton suggests that the creature’s habits differed in any important way from those of the genera last named.

†Megalocnus, of the Cuban Pleistocene, a member of this family, was apparently peculiar to the island and was probably derived from ancestors which in the Pliocene migrated from Central America. Aside from certain remarkable peculiarities of the teeth, this animal was more primitive, as well as smaller, than any other of the Pleistocene genera.

Although remains of †Gravigrada are comparatively common in all of the fossiliferous formations between the Pampean and the Santa Cruz, the material is too imperfect to throw any useful light upon the development of the various families. From the Santa Cruz beds, on the other hand, a great wealth of specimens has been obtained, and it is possible to give some fairly adequate account of the †ground-sloths of that time. These animals were then extremely abundant individually and of extraordinary variety; evidently, they were in a state of rapid expansion and divergent evolution along many lines, for hardly any two specimens are alike and therefore the satisfactory discrimination of species is well-nigh impossible. Yet, with all this remarkable variability, the range of structural differences was not great; the group was a very homogeneous and natural one, and separation into families was not obvious. Two of the three families were, however, unequivocally present in this fauna and the third somewhat doubtfully so. The †Megalonychidæ, which in the South American Pleistocene had dwindled to such insignificant proportions, formed the overwhelming majority of the Santa Cruz †Gravigrada; the †Mylodontidæ were quite rare in comparison and are still very incompletely known; while the †Megatheriidæ, though probably present, have not been identified beyond all doubt.

All of the Santa Cruz †ground-sloths were small animals, the largest not approximating the smallest Pleistocene species, those of Cuba excepted, and many of them were no larger than the modern tree-sloths. This was a wonderful difference between the Santa Cruz and the Pampean, but a difference which involved nearly all other groups of mammals. So far as the skeleton is concerned, this is known with completeness only for the †Megalonychidæ, especially the genus †Hapalops; but enough has been learned of the others to show that there was far less difference between the families than had arisen in the later epochs. This backward convergence of the three groups towards a common term plainly indicates their common origin, being exactly what might have been predicted in advance of experience.

In all the genera the teeth number 5/4; the teeth on each side were sometimes in continuous series, sometimes the first one was isolated and almost always more or less tusk-like, most so in †Eucholœops. The other teeth were usually of transversely elliptical shape and worn into two ridges, with a hollow between; the †mylodonts (†Nematherium, etc.) already had the triangular, or lozenge-shaped, lobate form of teeth, characteristic of the family.

The skull varied considerably in its proportions; generally, it was long and narrow, with shortened face and elongate cranium; the sagittal crest was seldom present, never prominent, and the orbit was always widely open behind, without postorbital processes. The premaxillaries were always short and toothless and in most of the genera they were slender rods, in others (e.g. †Hyperleptus) broad and plate-like. The lower jaw had an elongate spout-like symphysis, in which the two halves were coössified, tapering forward to a blunt point and, though the length of this spout differed greatly in the various genera, in none was there a broad, abrupt chin such as †Mylodon and †Megalonyx had. In †Prepotherium, which is believed to be referable to the †Megatheriidæ, the lower jaw had the extremely convex inferior border, in less exaggerated degree, of its huge Pampean successor; it would be premature to say descendant.

While the long, slender skull was the prevailing type among the Santa Cruz †Gravigrada, there was a group of small animals in which the skull was shorter and more rounded and had a very suggestive likeness to that of the modern tree-sloths, as was likewise true of the teeth.

Despite innumerable variations of detail, the skeleton of the Santa Cruz †ground-sloths may be described without distinction of genera, though it should be added that the skeleton is but partially known in many of the genera, and fuller knowledge might require modification of some of the statements. The neck was of moderate length, the body long, the tail long and heavy and, in some instances, very massive. The sternal ribs were completely ossified and already had the same elaborate mode of articulation with the breast-bone as in the great Pampean forms, and the vertebræ the same intricate connections. The shoulder-blade also had the same characteristics as in the latter, but the hip-bones had but a moderate transverse expansion, having no huge mass of viscera to support.

The limbs were stout and short, fore and hind legs of nearly equal length; the humerus had the epicondylar foramen and the broad, flattened femur retained the third trochanter. The radius had a discoidal upper end, which rotated freely upon the humerus; the tibia and fibula were always separate. The feet were five-toed, all the digits complete and functional and all provided with claws; there was no coössification between the phalanges. The astragalus was little different from the normal form, but in some genera (e.g. †Prepotherium) the highly peculiar form of this bone characteristic of †Mylodon and †Megatherium was distantly foreshadowed. The gait must have been simply plantigrade, though some of the forms had probably begun to throw the weight upon the outer edge of the foot.

No dermal armour has yet been found in association with any of the genera, and, so far as the predominant †Megalonychidæ are concerned, of which so many skeletons have been collected, this negative evidence must be allowed great weight. But the material of the other two families is so rare and incomplete, that the failure to find dermal ossicles is of no value in determining the question; probably, the †mylodonts possessed them.

These small Santa Cruz †ground-sloths were not so clumsy and slow-moving as their gigantic successors of the Pampean, and must have been inoffensive plant-eaters, some of them perhaps more or less arboreal in habits, but they could defend themselves with their long, sharp claws.

It would require far too much space and lead us into a labyrinth of anatomical technicalities to point out all the many resemblances to other edentate suborders which are to be noted in the skeleton of the Santa Cruz †Gravigrada, which thus justified their position as the most nearly central group of the entire order. Not only was the skeleton of these Miocene †ground-sloths very much less specialized than in their Pleistocene successors, but they were much closer to the anteaters than were the latter. Aside from the skull, all parts of the skeleton displayed this resemblance in so marked a manner that the common derivation of the two suborders seems hardly open to question. Different as was the skull in the two groups, the differences were not such as to preclude the origin of both from the same type. Even more closely connected were the †ground-sloths and the tree-sloths; the resemblance was most clear in the teeth and skull, but there were also many points of likeness throughout the skeleton. In the tree-sloths the entire bony structure has been profoundly modified in adaptation to their altogether exceptional mode of life, in hanging suspended from the branches of trees; but, despite this modification, there are so many notable resemblances between the Santa Cruz †Gravigrada and the existing Tardigrada as irresistibly to suggest their community of origin, and thus the former served to connect the anteaters, on the one hand, with the tree-sloths, on the other. This must not be construed as meaning that the Miocene †ground-sloths were the ancestors of the other suborders, which were probably already in existence as distinct groups, but merely that all three suborders had a common origin, from which the Santa Cruz †Gravigrada had departed less than have the sloths and anteaters.

There is evidence that at least two of the †ground-sloth families, the †Megalonychidæ and the †Mylodontidæ, were distinguishable in the Deseado stage, but materials are still lacking to give us any real knowledge of the suborder in that or the more ancient stages.

Section Loricata. Armoured Edentates

Suborder Dasypoda. Armadillos

Armadillos are still an important and characteristic element of the Neotropical fauna, ranging from Texas to Patagonia and showing a considerable variety of structure and appearance. Existing species are all of small or moderate size, and the one which is by far the largest (Priodontes gigas) may somewhat exceed three feet in length, exclusive of the tail, and the smallest (Chlamydophorus truncatus) is hardly more than five inches long. In most armadillos the hair is greatly diminished in quantity and the animal is sheathed in a conspicuous armour of bony scutes, covered with horny plates. There is a head-shield which covers the top of the skull, and the tail is enclosed in a sheath; the back and sides are protected by the great carapace and the limbs by irregular scutes and scales, leaving only the under side of the body and the inside of the legs uncovered. In most existing genera, the carapace is in three parts, an anterior and posterior buckler, in which the plates are immovably fixed together by their edges, and between a varying number of transverse, overlapping bands, from 3 to 13, which permit sufficient flexibility of the body. The tail-sheath is made up of a series of rings. One genus (Tolypeutes) has the power of rolling itself into a ball, the head-shield exactly closing the anterior notch of the carapace and the tail-sheath filling the posterior notch. The animal is thus perfectly protected against attack and does not seek refuge by digging, as other armadillos do and with astonishing rapidity. In the little Pichiciago (Chlamydophorus) the dermal ossifications are very thin and the carapace is composed of twenty transverse bands of horny plates, without bucklers; the rump is covered with a broad and heavy shield of bone, overlaid with thin plates of horn, which is attached to the hip-bones and notched below for the short tail. In certain rare and little known genera there is a greater development of hair; in one (Praopus) the whole carapace is covered with a dense coat of hair, and in another (Scleropleura) the middle of the back has only a hairy skin and the carapace is restricted to the sides.

The teeth vary in number and size in the different genera; in some (e.g. Dasypus) there is one upper incisor on each side; the teeth are all simple and of nearly cylindrical form. The skull is low and flattened, with long tapering snout and orbits widely open behind; the zygomatic arches are uninterrupted. Most of the vertebræ of the neck are fused into a single piece; in the lumbar and posterior dorsal regions there are not only the usual highly intricate articulations between the vertebræ, but also high processes on each side for the support of the carapace. The fully ossified sternal ribs have movable joints with the breast-bone, but not the double articulations found in the anteaters and †ground-sloths. The shoulder-blade has a very long acromion, which does not form a bony loop with the coracoid, and the clavicles are complete. The anterior element (ilium) of the hip-bone is narrow, very different from the broad plate of the †Gravigrada. The humerus has prominent deltoid and supinator ridges and an epicondylar foramen, and the femur has the third trochanter. Though the fore-arm bones are separate, the radius has no freedom of rotation; tibia and fibula are coössified at both ends.

In the hind foot there is no great variety of character; it is five-toed and usually has claws, but may have broad, flat nails (e.g. Priodontes), but the manus, which is a burrowing organ, displays different degrees of specialization, which is carried farthest in the Giant Armadillo (Priodontes). Tatu has the fore foot of quite different type. The armadillos feed chiefly upon insects and worms, but they are omnivorous and eat roots and carrion and sometimes even capture and devour small rodents and lizards.

As in the case of the †ground-sloths, the fossil armadillos so far available are insufficient for tracing the history of the various phyla, or for doing more than making a very brief sketch of the development of the suborder as a whole. Nearly all of the modern genera have been found in the Pleistocene together with several that are extinct, some of the latter of very large size. One of these, †Eutatus, had a carapace without bucklers and made up of 33 movable, transverse bands. Another, †Chlamydotherium, as large as a rhinoceros and the largest known armadillo, had anterior and posterior bucklers, with several movable bands between; it was especially characterized by the teeth, which were divided by a vertical groove into pillars or lobes, thus approximating the teeth of the †glyptodonts. The genus went far back into the Pliocene, and the more ancient species were successively smaller.

Though remains of armadillos abound in the formations between the Pampean and the Santa Cruz, they are for the most part so fragmentary as to be of no service in deciphering the history of the group. In the Santa Cruz beds also they are very abundant and varied, and several of the genera are very completely known. As a whole, this assemblage of armadillos was very different from that of the Pleistocene, and only a few direct ancestors of the latter have been found in the Miocene of Patagonia; no doubt, like the ancestral tree-sloths and anteaters, they were then living in the warmer regions of the north. Most of the Santa Cruz armadillos belonged to aberrant types, of which no descendants have survived; but, nevertheless, they throw welcome light upon the developmental stages of the suborder.