The Cambridge Natural History Part 13

{171} [Ill.u.s.tration]

FIG. 97.--Skull of Three-toed Sloth. _Bradypus tridactylus._ Lateral view.

_fr_, Frontal; _ju_, jugal; _lcr_, lachrymal; _max_, maxilla; _nas_, nasal; _par_, parietal; _s.oc_, supra-occipital; _ty_, tympanic. (From Parker and Haswell's _Zoology_.)

FAM. 2. BRADYPODIDAE.--The Sloths, genera _Bradypus_ and _Choloepus_, come, as already stated, very near to the Anteaters, in spite of their striking difference in appearance. The Sloths are purely arboreal creatures, with strong recurved claws, which serve as hooks to keep them suspended from the lower side of a branch. The three-toed sloth, _Bradypus_ (or "Ai"), has the exceptional number of nine cervical vertebrae; the two-toed sloth, _Choloepus hoffmanni_ (or "Unau"), has the equally exceptional number of six. The hair is long and s.h.a.ggy, and gets an advent.i.tious green colour from the presence of minute algae.[107] This gives to the animal the appearance of a lichen-covered bough, a resemblance which is increased in one species by an oval mark upon the back, which suggests forcibly a broken end of such a branch. The likeness of a Sloth to its surroundings is pointed out by Dr. Siemann,[108] who observed that a species occurring in Nicaragua "has almost exactly the same greyish-green colour as _Tillandsia usneoides_, the so-called 'Vegetable Horsehair' common in the district....

If it could be shown that it frequented trees covered with that plant ...

there would be a curious case of mimicry between the sloth's hair and the _Tillandsia_, and a good reason why so few of these Sloths are seen." The stomach in the Sloths is complicated in structure, with several chambers; one of these gives off a long crescent-shaped caec.u.m. The skull of the Sloths agrees in a number of particulars with that of the Anteaters. {172}

[Ill.u.s.tration]

FIG. 98.--Skeleton of Three-toed Sloth. _Bradypus tridactylus._ (After de Blainville.)

The zygoma is incomplete, though the part connected with the frontal has a strong downward process like that found in _Diprotodon_ and some other mammals. There is, moreover, a process from the squamosal, though it does not reach the anterior part and thus {173} complete the arcade. The premaxillaries are very small, and are usually lost in dried skulls.

Coupled with these points of likeness are some differences. The lower jaw, for instance, has a well-marked coronoid process. The pterygoids do not meet in the middle line. The teeth are five or four in each half of each jaw. There is no trace of a second set.

A peculiarity of the Sloths is the enormous number of dorsal vertebrae.

There are twenty-three of these in _Choloepus hoffmanni_, but only fifteen to seventeen in the Three-toed Sloth, _Bradypus_. As in other American Edentates, the acromion joins the coracoid. This connexion occurs in both the Two-toed and the Three-toed species. The limbs of these creatures are very long, a concomitant of an arboreal life. The femur has no third trochanter. The genus _Bradypus_, which by reason of the fact that it has not lost the third toe on the ma.n.u.s seems to be more primitive than _Choloepus_, shows another structural feature which does not bear out this conclusion. The trapezoid and the os magnum of the carpus are united, while in _Choloepus_ they are perfectly distinct bones.

The intestine has no caec.u.m.

There are several species of Sloths. Eminently perfect though the organisation of the Sloth in relation to its particular surroundings appears to us, Buffon selected the animal as the very type of imperfection in nature. "One more defect," he wrote, "they could not have existed."

FAM. 3. DASYPODIDAE.--The family Dasypodidae or Armadillos contains a considerable number of genera. _Tatusia_, _Tolypeutes_, _Dasypus_, _Xenurus_, _Priodon_,[109] and _Chlamydophorus_. They have all a more or less rigid covering of bony plates imbedded in the skin, which are not in the least comparable with the scales of the Manis. Save the Whales, in one or two genera of which traces of a dermal armature exist, the Armadillos are unique among existing mammals in this particular. The term "Edentate"

is especially inapplicable to the Armadillos; the genus _Priodon_ may have more than forty teeth in each jaw; a total of ninety was found in one specimen examined by Professor Kukenthal. In the tendency of the teeth to multiply, we have another example of a state of affairs which characterises so many Whales. Generally, however, seven to nine is the number of teeth in each {174} half jaw, of which one is often implanted in the premaxilla. The Armadillos show their alliance with the other American Edentates in the points enumerated above. Their teeth specially ally them to the Sloths, while the salivary and digestive organs generally are on the Anteater plan, but present a less extreme development. There are, however, caeca, paired as in birds, in the genera _Dasypus_ and _Chlamydophorus_. The others have none. But there is a dilatation at the commencement of the large intestine, which is not very different from the slightly-developed caeca of _Dasypus_.

There are certain peculiarities in the skeleton, which distinguish this family.

[Ill.u.s.tration]

FIG. 99.--Skull of Armadillo. _Dasypus s.e.xcinctus._ 2/3. _ex.oc_, Exoccipital; _fr_, frontal; _max_, maxilla; _nas_, nasal; _par_, parietal; _peri_, periotic; _p.max_, premaxilla; _s.oc_, supraoccipital; _sq_, squamosal; _ty_, tympanic. (From Parker and Haswell's _Zoology_.)

{175}

[Ill.u.s.tration]

[Ill.u.s.tration]

FIG. 100.--Bones of the right ma.n.u.s of the Hairy Armadillo. _Dasypus villosus._ 2/3. _c_, Cuneiform; _l_, lunar; _m_, magnum; _p_, pisiform; _R_, radius; _s_, scaphoid; _td_, trapezoid; _tm_, trapezium; _u_, unciform; _U_, ulna; _I-V_, digits. (From Flower's _Osteology_.)

FIG. 101.--Bones of the ma.n.u.s of the Great Armadillo. _Priodon giganteus._ 1/3. _a_, An accessory carpal ossicle in front of the pisiform, which is not seen in the figure. Other letters as in Fig. 100. (From Flower's _Osteology_.)

The skull in the Armadillos presents a number of likenesses to the other American Edentates.[110] The premaxillaries are small, but are larger in _Dasypus_ than in _Tatusia_. On the other hand the lachrymals are larger in the latter. The zygomatic arch is complete, but there is no downward process as in the Sloths. In _Tatusia_ (but not in _Dasypus_) the "short thick pterygoids add somewhat to the hard palate." This is clearly a beginning or a remnant of the quite crocodilian character of the palate of _Myrmecophaga_. In the cervical vertebrae we see the Whale-like character of fusion between individual vertebrae; and also, as in the Whales, the degree to which this fusion is carried out varies; two to four may be thus united. The additional articular facets upon the dorsal vertebrae have been already commented upon as a point of important likeness to other American Edentates. The dorsal vertebrae are commonly eleven in number, the lumbar being three. But in _Priodon_ the numbers are twelve and two respectively.

There are traces to be observed of the double-headed attachment of the ribs to the sternum. The shoulder girdle of the Armadillos is somewhat diverse in form in different genera; the acromion is always large, and is remarkable in _Priodon_ for the fact that the humerus also articulates with it, its extremity being recurved, and forming a socket for this purpose. As in some other Edentates there is a second spine on the scapula behind the first. The clavicle is strong. There is some variation in the form of the ma.n.u.s. It is five-fingered in _Dasypus_; in _Tolypeutes_ the first digit has vanished; on the other hand, in _Priodon_, the fifth has become rudimentary {176} and the third enormously enlarged. This latter fact recalls the arrangement characteristic of _Myrmecophaga_. The pelvis is greatly attached by the ischium to the vertebral column. The femur has a third trochanter.

The various forms of Armadillos are largely distinguished by the number of movable thin bands of scutes lying between the large anterior and posterior s.h.i.+elds. Thus we have _Dasypus s.e.xcinctus_, _Tolypeutes tricinctus_, etc.

[Ill.u.s.tration]

FIG. 102.--Pelvis and sacrum of Armadillo. _Dasypus s.e.xcinctus._ _ac_, Acetabulum; _il_, ilium; _isch_, ischium; _obt.for_, obturator-foramen; _pect.tub_, pectineal tubercle; _pub_, pubis. (From Parker and Haswell's _Zoology_.)

The little Pichi-chago (or, more correctly, Pichy-ciego), _Chlamydophorus_, which only grows to about 5 inches in length, has no movable bands at all.

It is covered with a uniform series of plates, which, moreover, are not discontinuous at the neck. It differs, too, from the prevailing Armadillo-type by the absence of conspicuous external ears. In the anterior part of the body the armature consists of little more than the h.o.r.n.y plates, which in other Armadillos overlie the bony dermal plates. In the hinder region the bony plates are strong. In this animal, therefore, we have the dermal armature reduced to a minimum; but it must be noticed that, like the extinct Glyptodons, the armature is continuous and nowhere ringed.

The genus _Tolypeutes_, of which the best-known species is _T. tricinctus_, the Apar (there are two other species in the genus), can roll itself up into a ball like the Pill-Millipede (_Glomeris_), and, protected by its armour, roll away from its enemies like the Arthropod under similar circ.u.mstances. This mode of protection, be it observed, is also adopted by the Pangolin and by the {177} Hedgehog. The genus has only three movable bands. The tail is short, and is covered with large tubercles. This genus is very markedly digitigrade when running.

[Ill.u.s.tration]

FIG. 103.--Three-banded Armadillo or Apar. _Tolypeutes tricinctus._ .

[Ill.u.s.tration]

FIG. 104.--Peludo Armadillo. _Dasypus s.e.xcinctus._ . (After Vogt and Specht.)

The Peludo, _Dasypus s.e.xcinctus_, is, like other Armadillos, an omnivorous creature, and appears to be particularly fond of carrion. It will burrow up to a decaying carcase like the ground-beetles. {178} Mr. W. H. Hudson has described the way in which this Armadillo will kill a snake by holding it down and literally sawing the reptile in half by help of the sharp and serrated edges of the carapace. _Dasypus_ has a very short tail, which is s.h.i.+elded by distinct rings near the base.

_Tatusia novemcincta_ is a species with nine movable bands. The genus has four teats; the ears are near together. There are no caeca and no azygos lobe to the lung. A species apparently belonging to this genus, but described under the generic names of _Cryptophractus_ and _Praopus_, is remarkable for the thick covering of hair, not entirely wanting but usually thin in other Armadillos. In this particular species the coat of hair is so thick as to conceal the underlying plates of the carapace. The individual hairs are stiff, and one inch and a half in length.[111]

The genus _Xenurus_ contains several species, the best known of which is inaptly named _X. unicinctus_. As a matter of fact the characteristic feature of the genus is the existence of twelve or thirteen movable plates between the two ends of the body. _X. unicinctus_ has twelve dorsal and three lumbar vertebrae. This Armadillo, known by the vernacular name of the Caba.s.sou, has one of the most modified hands that are found in the family.

The first two digits are slender and elongated; but are quite normal in the number of their phalanges. In the remaining three digits the metacarpal is short and broad, while the proximal phalanx is either suppressed altogether or fused with the metacarpal, the middle phalanx is present but short, while the third phalanx is very large indeed. As in _Dasypus_, but not as in _Tatusia_, which is in so many other respects divergent from these genera, the lungs have an azygos lobe. As a small point of difference, tending to show an alliance between the genera _Xenurus_ and _Dasypus_ and their difference from _Tatusia_, is the deeply-imbedded gall-bladder; this sac is not nearly so deeply plunged into the hepatic tissue in _Tatusia_.

_Xenurus_ has no caecal dilatations. The brain "is intermediate in its form and surface markings between _Dasypus_ and _Tolypeutes_." The small intestine is nearly eighteen times the length of the large. But these intestinal measurements are not of much avail in this group as marks of affinity, since in three species of _Dasypus_ Garrod gives the following widely-divergent lengths:--_D. villosus_, 11.5 feet and 1.25; _D. minutus_ {179} 5.1, with a large intestine of no less than 7 feet; _D. vellerosus_ 4.3 and .66.

_Priodon_ is the giant of its race. This Armadillo may reach a length of 3 feet to the base of the tail. The tail is some 20 inches long. The large number of teeth has been already noticed. There are twelve or thirteen bands. Other points in the structure of this genus have already been mentioned, and need not be recapitulated. This Armadillo feeds upon termites and carrion.

_Scleropleura_ is unfortunately but imperfectly known. The single species, named by Milne-Edwards[112] _S. bruneti_, is apparently a very rare inhabitant of Brazil. It is known by a single skin, which was tanned by the hunter who obtained it. Thus the hair, if any, has dropped out. The plates in the skin are deficient along the back and even upon the top of the head, and are barely represented upon the tail posteriorly. The ears are small and distant from each other. The tail is longish, about one-third of the length of the body. The total length of the creature including the tail is rather more than a foot and a half. The hunter who obtained it regarded it as a hybrid between an Armadillo and an Anteater.

EXTINCT XENARTHRA.--There are a good many extinct forms of Armadillo, apart of course from the Glyptodons. _Peltephilus_ is referred to later (p. 186).

_Dasypus_ was represented by a large form, 6 feet long, with a skull of one foot in length. The genus _Eutatus_ was also large. The carapace was formed of thirty-three distinct bands, of which the last twelve are soldered together, but not fused into a s.h.i.+eld as in _Dasypus_, etc.

An extinct group of American Edentates, termed the GRAVIGRADA,[113] are somewhat intermediate between the Sloths and the Anteaters. A number of the genera are well known from complete skeletons.

One of the typical forms of this group is _Mylodon_, which, together with its immediate allies, is often placed in a separate family, MYLODONTIDAE.

_Mylodon_ itself was a large creature, as big as a Rhinoceros. It was covered externally by armour in the skin, which did not form a ma.s.sive armature as in the Glyptodonts, but was in the {180} form of scattered plates, small and not fused together. The general aspect of the skull is decidedly Sloth-like. As in that animal, the malar bone is bifid posteriorly, and between the bifurcation is embraced the process of the squamosal. This latter is thus more developed than in the Sloth, but there is no actual union between it and the malar. The premaxilla is small. The lower jaw has both coronoid and ascending processes, and is ma.s.sive. There are five teeth on each side above, and four on each side below, as in the Sloths. There are the normal seven cervical vertebrae and sixteen dorsals.

The limbs are not long and slender,but short and strong, the animal having been terrestrial. The fore-feet were five-toed, of which the three inner toes had claws. The hind-feet were only four-toed, and the two inner only were clawed.

[Ill.u.s.tration]

FIG. 105.--_Mylodon robustus._ (Restoration, after Owen.)

_Scelidotherium_ is a genus which is a trifle smaller than the last. It has only four properly-developed toes in the fore-foot, the thumb being rudimentary; of these, the first two bear claws. The hind-feet are also four-toed. Like _Mylodon_, _Scelidotherium_ is a Pleistocene genus.

_Glossotherium_ has a skull very much like the last two genera; but it is remarkable for the fact that the nostrils instead of being unprotected with bone anteriorly are there closed by a plate of bone formed by the well-developed premaxillae, the nostrils appearing at the sides, and giving the skull a curious likeness to that of a Chelonian. From a series of recent and most important observations it appears to be clear that this genus has survived into quite modern times.[114]

{181}

The well-known naturalist of La Plata, Senor Moreno, engaged in studies connected with the political boundary line between Chili and the Argentine, had occasion to visit Consuelo Cove on Last Hope Inlet in Patagonia.

Hanging from a tree he noticed a piece of dried skin, which at once struck him as looking more like the remains of a Mylodon than of any living animal. The inhabitants regarded this piece of skin as a great curiosity, but were of opinion that it was the hide of a cow encrusted with pebbles!

This fragment from a bygone age was originally described by Professor Ameghino, who had apparently seen some of the bonelets imbedded in it, as _Neomylodon listai_, "a living representative of the ancient Gravigrade Edentates of Argentina." That this piece of skin is of quite recent date seems to be proved by a number of considerations. In the first place it is covered by long hair of a light yellowish-brown colour; it does not seem likely that hair would preserve its character for geological epochs. The nearest corresponding case is that of the remains of Moas in New Zealand, whose feathers, dried skin, and tendons are known. Now the Moa was unquestionably contemporaneous with man, as abundant surviving legends prove, and indeed it cannot have been long extinct. Still, hair is a resisting structure, and in a dry cave, with no possibility of irruptions of floods, might retain its characters for long periods. The evidence, however, of more recent date is stronger than this. The skin shows patches of reddish colour, suggestive of course of blood-stains. A small piece of the outside of the skin at the cut edge, which presented the appearance of freshly or comparatively freshly dried fluid, was submitted to a chemical examination and shown to be serum! Dr. Lonnberg examined chemically a bit of the skin itself and found in it, after boiling, glue, "which proves that the collagen and gelatinous substances are perfectly preserved." After this it seems impossible to suppose that the skin can be of any very great age; for bacteria would have finished their work upon the serum and gelatine long ago. Combined with the fresh appearance of the skin is the very fresh appearance of the skull. In fact it is impossible to believe that the animal was not alive quite a few years since, relatively speaking. It is admitted that this animal was contemporaneous with man. There are actually legends of a creature which may have been this _Glossotherium_. "Ancient chroniclers inform us that the indigenous inhabitants recorded the existence of a {182} strange, huge, ugly monster, which had its abode in the Cordillera to the south of lat.i.tude 37. The Tehuelches and the Gennakens have mentioned similar animals to me, of whose existence their ancestors had transmitted the remembrance; and in the neighbourhood of Rio Negro, the aged Cacique Sinchel, in 1875, pointed out to me a cave, the supposed lair of one of these monsters, called 'Ellenga.s.sen'; but I must add that none of the many Indians with whom I have conversed in Patagonia have ever referred to the actual existence of animals to which we can attribute the skin in question."