1911 Encyclopædia Britannica/Edentata
EDENTATA, the name assigned by Cuvier to an order of placental mammals apparently typified by the South American anteater, but likewise including the sloths and armadillos of the same country, and the Old World aard-varks and pangolins. Only the anteaters and pangolins are absolutely without teeth (Lat. e, out, dens, tooth), and the name is strictly applicable only to those two groups; but in all the existing representatives of the order teeth are absent from the front of the jaws, while the cheek-teeth are devoid of roots and of enamel, and only very exceptionally have deciduous predecessors. Practically this is all the definition that can be given to the assemblage, which is possibly an artificial one. It may be mentioned, however, that there is not unfrequently a separate coracoid bone.
Edentates may be divided into three distinct sections or suborders, firstly the Xenarthra, or Edentata Vera, of America, secondly the Tubulidenta, represented by the African aard-varks, and thirdly the Pholidota, which includes only the pangolins common to Africa and Asia. The Xenarthra are essentially a South and Central American group, some of the members of which have effected an entrance into North America. The three families by which they are now represented are widely sundered, both as regards habits and structure; but two of them—the sloths and the anteaters—are intimately connected by means of the extinct ground-sloths. As regards the presumed relationship of the Old World to the New World types, it is noteworthy that in the early Tertiary deposits of France and Germany are found certain fossil remains apparently referable to armadillos, aard-varks and pangolins, some of the armadillos coming very close to South American forms. This assemblage of three groups of edentates in the countries fringing northern Africa is suggestive that the latter continent may have been the original home of the group, which reached South America by means of a direct land connexion.
Xenarthra.—The typical American edentates, or Xenarthra, are characterized by the circumstance that the last dorsal and all the lumbar vertebrae carry additional articular facets, or abnormal articulations (xenarthral). Teeth may be absent or present, and when developed either all similar (homaeodont) or to some extent differentiated. The bodily covering may take the form either of coarse hairs, or of bony plates, with a larger or smaller intermixture of hairs.
|Fig. 1.—Skull of Unau or Two-toed Sloth (Choloepus didactylus).|
Of the three existing families of this group, the first is that of the Bradypodidae, or sloths, characterized by the presence of five pairs of upper and four of lower teeth, the normally-formed tongue and the rudimentary tail. The species are arboreal and feed on leaves; all being confined to the forests of tropical America. Externally sloths are clothed with long coarse, crisp hair; the head is short and rounded, and the external ears inconspicuous. The teeth are subcylindrical, of persistent growth, consisting of a central axis of vasodentine, with a thin investment of hard dentine, and a thick outer coating of cement; without any succession. Fore-limbs greatly longer than the hind-limbs; the extremities terminating in narrow, curved feet; with the digits never exceeding three in number, and encased for nearly their whole length in a common integument, and armed with long, strong claws. Stomach complex. No caecum. Placenta deciduate and dome-like, composed of an aggregation of numerous discoidal lobes.
A remarkable feature connected with sloths is the development of a green colour in their hair, due to the growth of an alga. According to Dr W. G. Ridewood, in the three-toed sloth the hair is invested with a thick extra-cortical layer. “The hair has a tendency to crack in a transverse direction, and in the cracks there come to lodge unicellular algae, to which Kühn has given the name Pleurococcus bradypi. The moisture of the climate in which Bradypus lives enables the alga to live and propagate in this curious position, and the sloth acquires a general green tint which must render it very difficult to distinguish as it hangs among the green foliage.” In the two-toed sloth, on the other hand, the bulk of the hair is composed of an outer coat, or cortex, which is longitudinally fluted or grooved, the grooves being filled with strands of extra-cortex in which flourishes an alga (Pleurococcus choloepi) distinct from the one infesting the hairs of the three-toed species. Of quite a different type are the hairs of the extinct ground-sloths (see Mylodon), which are smooth and solid, Dr Ridewood rejecting the idea that they were originally coated with a cortex that has disappeared.
The typical genus Bradypus is represented by the various species of ai, or three-toed sloth, in which none of the teeth project greatly beyond the others; the first in the upper jaw is much smaller than any of the others, while the first in the lower jaw is broad and compressed, and the grinding surfaces of all are much cupped. Vertebrae: C 9, D and L 20 (of which 15 to 17 bear ribs), S 6, Ca 11. All the species present the peculiarity of possessing nine cervical vertebrae; but the ninth, and sometimes the eighth, bears a pair of short movable ribs. The fore-limbs are considerably longer than the hind-legs, and the bones of the fore-arm are complete, free and capable of pronation and supination. The fore-feet are long, very narrow, habitually curved and terminate in three pointed curved claws, in close apposition to each other; they are, in fact, incapable of being divaricated, so that the foot is reduced to the condition of a triple hook, fit only for the function of suspension from the boughs of trees. The hind-foot closely resembles the fore-foot in general structure and mode of use, and has the sole habitually turned inwards so that it cannot be applied to the ground in walking. The tongue is short and soft, and the stomach large and complex, bearing some resemblance to that of ruminants. The windpipe or trachea has the remarkable peculiarity—not unfrequent among birds and reptiles—of being folded on itself before it reaches the lungs. The two teats are pectoral in position. The premaxilla is rudimentary and loosely attached to the maxilla. Except in B. torquatus, there is no perforation in the lower end of the humerus. Some of the species are covered uniformly with a grey or greyish-brown coat; others have a dark collar of elongated hairs around the shoulders (B. torquatus); some have the hair of the face shorter than that of the rest of the head and neck; and others have a remarkable-looking patch of soft, short hair on the back between the shoulders, consisting, when best marked, of a median stripe of glossy black, bordered on each side by bright orange, yellow or white. There are also structural differences in the skulls, as in the amount of inflation of the pterygoid bones. The habits of all are apparently alike. They are natives of Guiana, Brazil and Peru, and two species (B. infuscatus and B. castaneiceps) extend north of the Isthmus of Panama as far as Nicaragua. Of the former of these a specimen in captivity uttered a shrill sound like a monkey when forcibly pulled away from the tree to which it was holding.
In the species of unau, or two-toed sloths, Choloepus, the front tooth in both jaws is separated by an interval from the others, and is large and caniniform, wearing to a sharp bevelled edge against the opposing tooth, the upper shutting in front of the lower when the mouth is closed, unlike true canines. Vertebrae: C 6 or 7, D 23-24, L 3, S 7-8, Ca 4-6. One species (C. didactylus) has the ordinary number of vertebrae in the neck; but an otherwise closely allied form (C. hoffmanni) has but six. The tail is very rudimentary. The fore-feet generally resemble those of Bradypus, but there are only two functional digits, with claws; these answering to the second and third of the typical five-toed limb. The structure of the hind-limb generally resembles that of Bradypus, the appellation “two-toed” referring only to the anterior limb, for in the foot the three middle toes are functionally developed and of nearly equal size. The premaxilla is well developed, and firmly attached to the maxilla; and there is always a perforation, or foramen, on the inner side of the lower end of the humerus. C. didactylus, which has been longest known, and is commonly called by the native name of unau, inhabits the forests of Brazil. C. hoffmanni has a more northern geographical range, extending from Ecuador through Panama to Costa Rica. Its voice, which is seldom heard, is like the bleat of a sheep, and if the animal is seized it snorts violently. Both species are very variable in external coloration (see Sloth).
The second family is that of the anteaters, Myrmecophagidae, distinguished from the last by the absence of teeth, the elongated tongue and the long tail. The long and slender head has a tubular mouth, with a small terminal aperture through which the worm-like tongue, covered with the sticky secretion of the enormous submaxillary salivary glands, is rapidly protruded in feeding, and withdrawn again with the adhering particles of food which are then sucked into the gullet. In the foot the third toe is greatly developed, and has a long sickle-like claw; the others are reduced or suppressed. The hind-foot has four or five subequal digits with claws. The long tail is sometimes prehensile. Placenta dome-like or discoidal. Externally the body is covered with hair. Anteaters feed exclusively on animal substances, mostly insects. One species is terrestrial, the others arboreal; none burrow in the ground. They are all inhabitants of tropical America. In the typical genus Myrmecophaga the skull is remarkably elongated and narrow, with its upper surface smooth and cylindriform. Anteriorly the face is produced into a long tubular rostrum, rounded above and flattened below, with terminal nostrils, and composed of the mesethmoid (ossified for more than half its length), the vomer, the maxillae, and the long and narrow nasal bones, the premaxillae being extremely short and confined to the margin of the nostrils. The zygomatic arch is incomplete, the rod-like jugal only articulating with the maxilla in front, and not reaching the short zygomatic process of the squamosal. The lachrymal foramen is in front of the margin of the orbit. There are no post-orbital processes to the frontals or any other demarcation between the orbits and the temporal fossae. Palate extremely elongated, and produced backwards as far as the level of the external auditory meatus by the meeting in the middle line of the largely developed pterygoids. The glenoid fossa for the lower jaw, a shallow oval facet, with its long diameter from before backwards. Lower jaw long and slender, with an exceedingly short symphysis, no distinct coronoid process, and a slightly elevated, elongated, flattened, condylar articular surface. Vertebrae: C 7, D 15-16, L 3-2, S 6, Ca 31. Clavicles rudimentary. In the fore-foot the first digit is very slender, the second also slender, with compressed phalanges of nearly equal length, but the third is immensely developed, though its first phalanx is extremely short, while the terminal one is so long that the entire length of the digit exceeds that of the second. The fourth has a long and rather slender metacarpal, and three phalanges diminishing in size, the terminal phalange being very small. The fifth has the metacarpal nearly as long, but not so stout as the fourth, and followed by two small phalanges, the last rudimentary and conical. Claws are developed upon all but the fifth. In walking the toes are kept bent, with their points turned upwards and inwards, the weight being supported on a pad over the end of the fifth digit, and the upper surfaces of the third and fourth digits. The hind feet are short and rather broad, with five subequal claws, the fourth rather longest, the first shortest; the whole sole is placed on the ground in walking. Body rather compressed, clothed with long, coarse hair. Tail about as long as the body, and covered with very long hair; not prehensile. Ears small, oval, erect. Eyes very small. Stomach consisting of a sub-globular, thin-walled, cardiac portion, and a muscular pyloric gizzard with dense epithelial lining. No ileocolic valve; but a short, wide, ill-defined caecum. The two teats are pectoral.
The tamandua anteaters (Tamandua, or Uroleptes), of which several species (or races) are now recognized, are smaller animals than the last, in which the head is much less elongated, the fur short and bristly, and the tail, tapering, prehensile, with the under side throughout, and the whole of the terminal portion naked and scaly. The stomach is similar to that of Myrmecophaga, but with the muscular pyloric gizzard less strongly developed. There is a distinct ileocolic valve and short globular caecum. The fore-foot has a very large claw on the third toe, moderate-sized claws on the second and fourth, a minute one on the first, and none on the fifth, which is entirely concealed within the skin. The hind-foot has five subequal claws. Vertebrae: C 7, D 17, L 2, S 5, Ca 37. There are very rudimentary clavicles.
|Fig. 2.—Tamandua Anteater (Tamandua tetradactyla).|
The last representative of the family is the tiny golden-haired pigmy or two-toed anteater, Cyclopes (or Cycloturus) didactylus, in which the skull is much shorter even than in the preceding genus, and arched considerably in the longitudinal direction. It differs from that of the other members of the family mainly in the long canal for the posterior nostrils not being closed by bone below, as the greater part of the palatines and the pterygoids do not meet in the middle line. The lower jaw has a prominent, narrow, recurved coronoid, and a well-developed angular process, and is strongly decurved in front. Vertebrae: C 7, D 16, L 2, S 4, Ca 40. Ribs remarkably broad and flat. Clavicles well developed. Fore-foot remarkably modified, having the third digit greatly developed at the expense of all the others; it has a short stout metacarpal and but two phalanges, of which the terminal one is large, compressed, pointed and much curved, with a strong hook-like claw. The second digit has the same number of phalanges, and bears a claw, but is much more slender than the third. The fourth is represented only by the metacarpal, and one nailless phalange, the first and fifth only by rudimentary metacarpals. The hind-foot is also modified into a climbing organ, the first toe being rudimentary and consisting of a metatarsal and one phalange concealed beneath the skin, but the other four toes subequal and much curved, with long, pointed, compressed claws. The tuberosity of the heel-bone or calcaneum is directed towards the sole, and parallel with it and extending to about double its length is a greatly elongated sesamoid ossicle. These together support a prominent cushion to which the nails are opposed in climbing. Stomach pyriform, with muscular walls, but no distinct gizzard-like portion. The commencement of the colon provided with two small caeca, narrow at the base, but rather dilated at their terminal blind ends, and communicating with the general cavity by very minute apertures. Tail longer than the body, tapering, bare on the under surface and prehensile. Fur soft and silky.
The third and last existing family of the Xenarthra is that of the armadillos, or Dasypodidae, in which there are at least seven pairs of teeth in each jaw, while the tongue is normal, the tail generally long, and the body covered with an armour of bony plates overlain by horny scales. All the species are terrestrial, and insectivorous or more or less omnivorous.
The union of the numerous polygonal bony shields on the back and sides forms a hard shield, usually consisting of an anterior (scapular) and posterior (pelvic) solid portion (which overhang on each side the parts of the body they respectively cover, forming chambers into which the limbs are withdrawn), and a variable number of rings between, connected by soft flexible skin so as to allow of curvature of the body. The top of the head has also a similar shield, and the tail is usually encased in bony rings or plates. The outer or exposed surfaces of the limbs are protected by irregular bony plates, not united at their margins; but the skin of the inner surface of the limbs and under side of the body is soft and more or less clothed with hair. Hairs also in many species project through apertures between the bony plates of the back. The bony plates are covered by a layer of horny epidermis. Teeth numerous, simple, of persistent growth and usually without milk predecessors. Zygomatic arch of skull complete. Cervical vertebrae with extremely short, broad and depressed bodies; the first free, but the second and third, and often several of the others united together both by their bodies and arches. Clavicles well developed. A third trochanter on the femur. Tibia and fibula united at their lower extremities. Fore-feet with strongly developed, curved claws, adapted for digging and scratching, three, four or five in number. Hind-feet plantigrade, with five toes, all provided with nails. Tongue long, pointed and extensile, though to a less degree than in the anteaters. Submaxillary glands largely developed. Stomach simple. Placenta discoidal and deciduate.
The typical genus Dasypus, with several others, represents the subfamily Dasypodinae, which usually have all five toes developed and with nails, though the first and fifth may be suppressed. The first and second are long and slender, with the normal number and relative length of phalanges, the others stout, with short broad metacarpals, and the phalanges reduced in length and generally in number by coalescence; the terminal phalange of the third being large, that of the others gradually diminishing to the fifth. Dasypus has the most normal form of fore-foot, but the modifications developed in all the others (culminating in Tolypeutes) are foreshadowed. Ears wide apart. Teats, one pair, pectoral. In Dasypus the teeth are 9⁄10 or 8⁄9, of which the first in the upper jaw is usually implanted in the premaxillary bone. The series extends posteriorly some distance behind the anterior root of the zygoma, almost level with the hind edge of the palate. The teeth are large, subcylindrical, slightly compressed, diminishing in size towards each end of the series; the anterior two in the lower jaw smaller and more compressed than the others. Cranial portion of the skull broad and depressed, facial portion triangular, broad in front and depressed. Auditory bulla completely ossified, perforated on the inner side by the carotid canal, and continued externally into an elongated bony meatus auditorius, with its aperture directed upwards and backwards. (In all the other genera of Dasypodinae the tympanic bone is a mere half-ring, loosely attached to the cranium.) Lower jaw with a high ascending branch, broad transversely placed condyle, and high slender coronoid process. Vertebrae: C 7, D 11-12, L 3, S 8, Ca 17-18. Head broad and flat above, with the muzzle obtusely pointed. Ears of moderate size or rather small, placed laterally far apart. Body broad and depressed. Armour with six or seven movable bands between the scapular and pelvic shields. Tail shorter than the body, tapering, covered with plates forming distinct rings near the base. Fore-feet with five toes; the first much more slender than the others, and with a smaller ungual phalange and nail; the second, though the longest, also slender. The third, fourth and fifth gradually diminishing in length, all armed with strong, slightly curved compressed claws, sloping from an elevated, rounded inner border to a sharp, outer and inferior edge. The hind-foot is rather short, and has all five toes armed with stout, compressed, slightly curved, obtusely pointed claws—the third the longest, the second nearly equal to it, the fourth the next, the first and fifth shorter and nearly equal.
To this genus belongs one of the best-known species of the group, the six-banded armadillo or encoubert (D. sexcinctus) of Brazil and Paraguay; a very similar species, D. villosus, the hairy armadillo, replacing it south of the Rio Plata. There are also two small species, D. vellerosus and D. minutus, from the Argentine Republic and North Patagonia; the latter, which differs from the other three in having no tooth implanted in the premaxillary bone and is often referred to a genus apart, as Zäedius.
In Tatoua (Cabassous or Lysiurus) the teeth are 9⁄9 or 8⁄8, of moderate size and subcylindrical: the most posterior placed a little way behind the anterior root of the zygoma, but far from the hinder margin of the palate. Skull somewhat elongated, much constricted behind the orbits, and immediately in front of the constriction considerably dilated. Lower jaw slender, with the coronoid process small and sharp pointed, sometimes obsolete. Vertebrae: C 7, D 12-13, L 5, S 10, Ca 18. Head broad behind. Ears rather large and rounded, wide apart. Movable bands of armour 12-13. Tail considerably shorter than the body, and slender, covered with nearly naked skin, with a few small, scattered, bony plates, chiefly on the under surface and near the apex. On the fore-feet the first and second toes are long and slender, with small claws and the normal number of phalanges. The other toes have but two phalanges; the third has an immense sickle-like claw; the fourth and fifth similar but smaller claws. The hind-feet are comparatively small, with five toes, and small, triangular, blunt nails; the third longest, the first shortest. The best-known species of this genus, the tatouay or cabassou, T. unicinctus, is, after Priodon gigas, the largest of the group. It is found, though not abundantly, in Surinam, Brazil and Paraguay. Others, such as T. hispidus and T. lugubris, have been described.
In the giant armadillo (Priodon gigas) the teeth are variable in number, and generally differ on the two sides of each jaw, being usually from 20 to 25 on each side above and below, so that as many as a hundred may be present altogether; but as life advances the anterior teeth fall out, and all traces of their sockets disappear. The series extends as far back as the hinder edge of the anterior root of the zygoma. They are all very small, in the anterior half of each series strongly compressed, with flat sides and a straight free edge, but posteriorly more cylindrical, with flat, truncated, free surfaces. Vertebrae: C 7, D 12, L 3, S 10, Ca 23. Head small, elongated, conical. Ears moderate, ovate. Armour with 12-13 movable bands. Tail nearly equal to the body in length, gradually tapering, closely covered with quadrangular scales, arranged in a quincunx pattern. Fore-feet with five toes, formed on the same plan as those of Tatoua, but with the claw of the third of still greater size, and that of the others, especially the fifth, proportionally reduced. Hind-foot short and rounded, with five very short toes, and short, broad, flat obtuse nails. The giant armadillo is by far the largest existing member of the family, measuring rather more than 3 ft. from the tip of the nose to the root of the tail, the tail being about 20 in. long. It inhabits the forest of Surinam and Brazil. The powerful claws of its fore-feet enable it to dig with great facility; and its food consists chiefly of termites and other insects, although it is said to attack and uproot newly-made graves for the purpose of devouring the flesh of the bodies contained in them.
The apar (Tolypeutes tricinctus) typifies a genus in which the teeth are 9⁄9 or 8⁄9, and are rather large in proportion to the size of the skull, with the hinder end of the series reaching nearly to the posterior margin of the palate. Vertebrae: C 7, D 11, L 3, S 12, Ca 13. Ears placed low on the sides of the head, rather large, broadly ovate. Armour with its scapular and pelvic shields very free at the sides of the body, forming large chambers into which the limbs can be readily withdrawn, and only three movable bands. Tail short, conical, covered with large bony tubercles. The fore-feet formed on the same type as in the last genus, but the peculiarities carried to a still greater extent. The claw of the third toe is very long, while those of the first and fifth are greatly reduced and sometimes wanting. On the hind-foot the three middle toes have broad, flat, subequal nails, forming together a kind of tripartite hoof; the first and fifth much shorter, with more compressed nails.
The armadillos of this genus have the power of rolling themselves up into a ball, the shield on the top of the head and the tuberculated dorsal surface of the tail exactly fitting into and filling up the apertures left by the notches at either end of the body-armour. This appears to be their usual means of defence when frightened or surprised, as they do not burrow like the other species. They run very quickly, with a very peculiar gait, only the tips of the claws of the fore-feet touching the ground. In addition to the apar, there are the Argentine and Bolivian T. conurus, and T. muriei from Argentina or Patagonia.
The last group of existing armadillos forms the genus Tatusia and the subfamily Tatusiinae; the subfamily rank being based on the fact that of the seven or eight pairs of small subcylindrical teeth, all but the last, which is considerably smaller than the rest, are preceded by milk-teeth not changed until the animal has nearly attained full size. Vertebrae: C 7, D 9-11, L 5, S 8, Ca 20-27. Head narrow, with a long, narrow, subcylindrical obliquely truncated snout. Ears rather large, ovate and erect, placed close together on the occiput. Armour with seven to nine distinct movable bands. Body generally elongated and narrow. Tail moderate, or long, gradually tapering; its plates forming distinct rings for the greater part of its length. Fore-feet with four visible toes, and a concealed clawless rudiment of the fifth; the claws long, slightly curved, and slender, the third and fourth subequal and alike, the first and fourth much shorter. Hind-feet with five toes, armed with strong, slightly curved, conical, obtusely pointed nails, and the third longest, then the second and fourth, and the first and fifth much shorter than the others. This genus differs from all the other armadillos in having a pair of inguinal teats in addition to the usual pectoral pair, and in producing a large number (4 to 10) of young at a birth, all the others having usually but one or two. The peba armadillo, T. septemcincta, is a well-known species, having an extensive range from Texas to Paraguay. It is replaced in the more southern regions of South America by a smaller species, with shorter tail, the mulita (T. hybrida) so called from the resemblance of its head and ears to those of a mule. T. kappleri is a large species from Guiana.
Finally we have the pichiciago, or fairy armadillo, Chlamydophorus truncatus, typifying the subfamily Chlamydophorinae. In most anatomical characters, especially the structure of the fore-foot, this group resembles the Dasypodinae, but it differs remarkably from all other known armadillos, living or extinct, in the peculiar modification of the armour.
The teeth, which number 8⁄8-9, are subcylindrical, somewhat compressed, moderate in size, and smaller at each end (especially in front) than at the middle of the series. Skull broad and rounded behind, pointed in front. Muzzle subcylindrical and depressed. A conspicuous rounded rough prominence on the frontal bone, just before each orbit. Tympanic prolonged into a tubular auditory meatus, curving upwards round the base of the zygoma. Vertebrae: C 7, D 11, L 3, S 10, Ca 15. Upper part of head and trunk covered with four-sided horny plates (with small thin ossifications beneath), forming a shield, free and overhanging the sides of the trunk, and attached only along the middle line of the back. The plates are arranged in a series of distinct transverse bands, about twenty in number between the occiput and the posterior truncated end, and not divided into solid scapular and pelvic shields with movable bands between. The hinder end of the body is abruptly truncated and covered by a vertically placed, strong, solid, bony shield, of an oval (transversely extended) form, covered by thin horny plates. This shield is firmly welded by five bony processes to the hinder part of the pelvis. Through a notch in the middle of its lower border the tail passes out. The latter is rather short, cylindrical in its proximal half, and expanded and depressed or spatulate in its terminal portion, and covered with horny plates. The dorsal surfaces of the fore and hind-feet are also covered with horny plates. The remainder of the limbs and under surface and sides of the body beneath the overlapping lateral parts of the back shield are clothed with rather long, soft silky hair. Eyes and ears very small, and concealed by the hair. Extremities short. Feet large, each with five well-developed claws, those on the fore-feet very long, stout and subcompressed, the structure of the digits being essentially the same as those of Tatoua and Priodon. Teats two, pectoral. Visceral anatomy closely resembling that of Dasypus, the caecum being broad, short and bifid. The pichiciago, a burrowing animal, about 5 in. long, inhabits the sandy plains of western Argentina, especially the vicinity of Mendoza. Its horny covering is pinkish, and its silky hair white. A second species, C. retusus, from Bolivia is rather larger and has the dorsal shield attached to the skin of the back as far as its edge, instead of only along the median line. (See Armadillo.)
Tubulidentata.—The second suborder of edentates, namely the Tubulidentata, is represented at the present day only by the aard-varks, or ant-bears, of Africa, constituting the family Orycteropodidae and the genus Orycteropus. Together with the following group, they differ from the Xenarthra in the absence of additional articular facets to the lumbar vertebrae; for which reason the term Nomarthra has been proposed for the Tubulidentata and Pholidota as collectively distinct from the Xenarthra. In the present group the external surface is scantily covered with bristle-like hairs. The teeth are numerous, and traversed by a number of parallel vertical pulp-canals. Femur with a third trochanter. Fore-feet without the first toe, but all the other digits well developed, with strong moderate-sized nails, suited to digging, the plantar surfaces of which rest on the ground in walking. Hind-feet with five subequal toes. Placenta broadly zonular. The brain is very like that of the Ungulata; and there are two pairs of teats, one abdominal, and the other inguinal. Aard-varks feed on animal substances; and are terrestrial and fossorial in habits. The total number of teeth is from eight to ten in each side of the upper, and eight in the lower jaw; but they are never all in place at one time, as the small anterior ones are shed before the series is completed behind. In the adult they number usually five on each side above and below, of which the first two are simple and compressed, the next two larger and longitudinally grooved at the sides, the most posterior simple and cylindrical. Their summits are rounded before they are worn; their bases do not taper to a root, but are evenly truncated and continually growing. Each tooth is made up of an aggregation of parallel dental systems, having a slender pulp cavity in the centre, from which the dentinal tubes radiate outwards, and being closely packed together each system assumes a polygonal outline as seen in transverse section. A series of milk-teeth is developed. Skull moderately elongated with the facial portion subcylindrical and slightly tapering, and the zygoma complete and slender. The palate ends posteriorly in the thickened transverse border of the palatines, and is not continued back by the pterygoids. The tympanic is annular, and not welded to the surrounding bones. The lower jaw is slender anteriorly, but rises high posteriorly, with a slender recurved coronoid, and an ascending pointed process on the hinder edge below the condyle, which is small, oval, and looks forward as much as upwards. Vertebrae: C 7, D 13, L 8, S 6, Ca 25. The large number of lumbar vertebrae is peculiar among Edentates. The tongue is less worm-like than in Myrmecophaga, being thick and fleshy at the base and gradually tapering to the apex. The salivary apparatus is developed much in the same manner as in that genus, but the duct of the submaxillary gland has no reservoir. The stomach consists of a large subglobular cardaic portion, with a thick, soft, and corrugated lining membrane, and a smaller muscular, pyloric part, with a comparatively thin and smooth lining. There is a distinct ileocaecal valve and a considerable sized caecum; also a gall-bladder. Head elongated, with a tubular snout, terminal nostrils and small mouth-opening. Ears large, pointed, erect. Tall nearly as long as the body, cylindrical, thick at the base, tapering to the extremity.
According to the researches of Dr E. Lönnberg, the teeth of the aard-varks correspond only to the roots of those of other mammals, the crowns being unrepresented, except to a very small degree when the teeth first cut the gum. This explanation renders the peculiar internal structure of these teeth much less difficult to understand than if they represented both crown and root. In Dr Lönnberg’s opinion, the teeth indicate the descent of the aard-vark from an ungulate stock,—a view in harmony with the evidence of the brain. If this idea prove well founded, and if the aard-varks are rightly classed with the Edentata, the whole order must apparently be regarded as an offshoot from primitive Ungulata. The fact of the frequent distinctness of the coracoid bone requires, however, explanation in connexion with such a descent (see Aard-Vark).
Pholidota.—The Pholidota, constituting the third and last group of the Edentata, are represented by the pangolins, or scaly anteaters, of Asia and Africa, all of which are included in the family Manidae and the genus Manis. Pangolins differ from all other mammals by the armour of overlapping horny scales (often with hairs growing between them) which invests the whole animal, with the exception of the under surface of the body, and sometimes a small patch near the tip of the under side of the tail. There are no teeth; and although the tongue is long and worm-like, it is not extensile. The scaphoid and lunar bones of the carpus are united. The uterus is bicornuate, and the placenta diffused and non-deciduate. The skull has somewhat the form of an elongated cone, with the small end turned forwards, and is smooth and free from crests and ridges. No distinction between the orbits and temporal fossae. The zygomatic arch usually incomplete, owing to the absence of the jugal bone; no distinct lacrymal bone; and the palate long and narrow. The pterygoids extend backwards as far as the tympanics, but do not meet in the middle line below. Tympanic welded to the surrounding bones, and more or less bladder-like, but not produced into a tubular auditory meatus. Two halves of lower jaw very slender and straight, without any angle or coronoid process, on the anterior extremity of the upper edge a sharp, conical, tooth-like process projecting upwards and outwards. No clavicles. No third trochanter to the femur. Terminal phalanges cleft at the tip. Caudal vertebrae with very long transverse processes and numerous chevron-bones. Stomach with thick muscular walls and lining membrane, and a special gland near the middle of the great curvature, consisting of a mass of complex secreting follicles, the ducts of which terminate in a common orifice. No caecum, but a gall-bladder. Head small, depressed, narrow, and pointed in front, with a very small mouth-opening. Eyes and ears very small. Body elongated, narrow. Tail more or less elongated, convex above, flat underneath. Limbs short, and in walking the surface and outer sides of the phalanges of the two outer digits of the front feet alone rest on the ground, with the points of the nails turning upwards and inwards. The third toe the longest, with a powerful compressed curved claw, the second and fourth with similar but smaller claws, but that of the first toe often almost rudimentary. Hind-feet plantigrade with the first toe very short, and the four other toes subequal, and carrying moderate, curved, compressed nails. Pangolins are of small or moderate size, terrestrial and burrowing, and feed mainly on termites or white ants; some of the species being more or less arboreal. They can roll themselves up in a ball when in danger. Their peculiar elongated form, short limbs, long tapering tail, and scaly covering give them on a superficial inspection more the appearance of reptiles than of mammals. The species are not numerous and may be divided into two sections, one comprising the Asiatic species, such as M. javanica, M. aurita of China, and the Indian M. pentadactyla, and the other the African, as represented by the large M. gigantea, M. temminchi, the long-tailed M. macrura, and the small arboreal M. tricuspis. In the Asiatic group the middle series of scales continues to the tip of the tail; but in the African forms this row splits into two a few inches from the tail-tip. The latter have also no hairs between the scales and no external ears. The climbing species have a small bare patch on the under side of the tail near the tip (see Pangolin).
Beyond remains of species closely allied to or identical with the existing forms, the sloths and anteaters appear to be unknown in a fossil state. On the other hand the extinct family of ground sloths, or Megatheriidae, which includes the largest of all edentates, is an exceedingly large one, and extends in South America from the Miocene to the Pleistocene, and was also represented during the latter epoch in North America. It serves to connect the Bradypodidae with Myrmecophagidae. The alleged occurrence of an allied form in Madagascar is somewhat doubtful (see Megatherium and Mylodon).
Of Dasypodidae numerous representatives occur in the South American Tertiaries. From the higher beds many of the species are referable to existing genera, such as Dasypus and Tatusia, although some are much larger than any living forms, the skull in one case being nearly a foot in length. In other instances, when lower formations are reached, the genera are also distinct, Eutatus having the whole armour divided into movable bands, and the allied Stegotherium representing the group in the Santa Cruz formation of Patagonia. Even in the Argentine Pleistocene there is an extinct genus, Chlamydotherium, represented by a species of the size of a rhinoceros, with grooved teeth approximating to those of the glyptodonts. The latter represent a family (Glyptodontidae) by themselves, and typically may be described as giant solid-shelled armadillos, although some of their smaller Santa Cruz representatives (Propalaeohoplophorus) approximate in some degree to true armadillos (see Glyptodon).
A very remarkable Santa Cruz armadillo, Peltephilus, has an altogether peculiar type of head-shield, developed into horns in front of the eyes; and, what is still more noteworthy, teeth in the front of the jaws, thereby rendering the ordinary definition of the order Edentata incorrect. It has been made the type of a distinct family, Peltephilidae.
The past history of the armadillo group does not, however, by any means end here. True armadillos, it should be observed, are known in North America as far north as Texas, from the Pleistocene onwards; but in formations of middle Tertiary age are unrepresented. Recent discoveries apparently indicate, however, the occurrence of armadillos of a primitive type in the lower Tertiary or Eocene formations of Wyoming. The first evidence of these Eocene armadillos was afforded by portions of the jaws, which, together with a leg-bone of a totally different animal, were believed to indicate creatures nearly allied to the aye-aye (Chiromys) of Madagascar, and for which the name Metachiromys was consequently proposed. According to modern usage, this name, in spite of its inappropriate nature, is retained for the armadillos, although in the writer’s opinion it ought to be replaced. According to Professor H. F. Osborn, by whom their remains have been described, the North American fossil armadillos were closely related to the existing members of the group, from which they differ chiefly by the armour, or shield, having probably been formed of tough leathery skin instead of bony plates, by the presence of a single pair of large enamel-capped tusk-like teeth in each jaw, and by the degeneration of the other teeth. If these determinations are trustworthy, the question arises whether we should regard the armadillos of South America as the descendants of North American forms which migrated southwards before that separation of the two continents was established, which lasted for a large portion of the Tertiary period, or whether a migration took place at the same early epoch in the opposite direction.
More interesting still is the occurrence of remains of reputed armadillos (Necrodasypus) from the Oligocene of France and Germany. In the opinion of Dr F. Ameghino these Oligocene armadillos, which had bony shields on both the head and body, were near akin to some of the modern South American forms.
Passing on to the aard-varks (Orycteropodidae), we find these represented by a species closely allied to the existing ones in the Lower Pliocene formations of Spain, France, Hungary, Samos and Asia Minor. A single tibia from the French Oligocene is identified by Dr Ameghino with the present family, and the genus Archaeorycteropus established for its reception; this genus, in its founder’s opinion, being also represented in the Santa Cruz beds of Patagonia. As regards the pangolins, the only fossils referred to this group (apart from a few discovered in a cave in India) appear to be certain limb-bones from the Oligocene of France and Germany, for which the names Necromanis and Teutomanis have been proposed. The occurrence of the characteristic cleft terminal toe-bones among these remains seems to leave little doubt as to the correctness of the determination.
The alleged occurrence of remains of giant pangolins in the upper Tertiary of Europe is due to misidentification (see Ancylopoda). By some authorities the Eocene group of Ganodonta has been affiliated to the Edentata, but this reference is not accepted by Prof. W. B. Scott.