CHAPTER XII.

GIANT SLOTHS AND ARMADILLOS.

"Injecta monstris terra dolet suis."

Horace, _Odes_, book iii.

It would have been strange, considering how much we owe to North America, had the great South American continent not enriched our knowledge of past forms of life on the globe. But such is not the case. The honours are, as it were, divided, although it must be admitted that the North American extinct forms at present known are far more numerous. There are, however, two or three "Extinct Monsters" of very great interest which once had a home in South America--in that strange region of the Pampas, where the naturalist of the present day finds so much to excite his interest. Of these the present chapter treats.

The Megatherium[48] (Cuvier) was a gigantic mammal allied to sloths and ant-eaters, and perhaps to the armadillos. In its skull and teeth this colossus of the past resembled the sloths, in its limbs and backbone it resembled the ant-eaters, while in size it surpassed the largest rhinoceros (Plate XVII.). The famous, but imperfect, specimen at Madrid was for a long time the principal if not the only source of information with regard to this extinct genus, and for nearly a century it remained unique.

[48] Greek--_megas_, great; _therion_, beast.

Later on, however, the zeal and energy of Sir Woodbine Parish, his late Majesty's _chargé-d'affaires_ at Buenos Ayres, greatly helped to augment the materials for arriving at a just conclusion with regard to its proper place in the animal kingdom. According to one writer, Spain formerly possessed considerable parts of three different skeletons. The first and most complete is that which is preserved in the royal cabinet at Madrid. This was sent over in 1789, by the Marquis of Loreto, Viceroy of Buenos Ayres, with a notice stating that it was found on the banks of the river Luxan. In 1795 a second specimen arrived from Lima, and other portions, probably not very considerable, were in the possession of Father Fernando Scio, to whom they had been presented by a lady from Paraguay. But two German doctors, Messrs. Pander and D'Alton, who published in 1821 a beautiful monograph on the subject, state that they were unable in 1818 to find any traces of either the Lima specimen or that which had belonged to Fernando Scio.

The remains collected by Sir Woodbine Parish were discovered in the river Salado, which runs through the flat alluvial plains (Pampas) to the south of the city of Buenos Ayres, after a succession of three unusually dry seasons, "which lowered the waters in an extraordinary degree, and exposed parts of the pelvis to view as it stood upright in the bottom of the river."[49]

[49] "Some Account of the Remains of the _Megatherium_ sent to England from Buenos Ayres, by Woodbine Parish, Jun., Esq., F.R.S.," by Wm. Clift, Esq., F.R.S., _Geological Transactions_, second series, vol. iii. p. 437.

This and other parts having been carried to Buenos Ayres by the country people, were placed at the disposal of Sir Woodbine Parish by Don Hilario Sosa, the owner of the property on which the bones were found. A further inquiry was instituted by Sir Woodbine; and on his application, the governor granted assistance, the result of which was the discovery of the remains of two other skeletons on his Excellency's properties, at no great distance from the place where the first had been found. It was in the year 1832 that Sir Woodbine Parish sent his valuable collection of bones from Buenos Ayres, and presented them to the Royal College of Surgeons. These specimens formed the subject of Mr. Clift's memoir above quoted. But even then the materials were not complete for a thorough knowledge of the bony framework of the Megatherium, and it was not till 1845, when more remains (discovered near Luxan, 1837) reached this country, that Professor Owen was able to clear up one or two doubtful details. These were purchased by the trustees of the British Museum, and casts of the bones were taken. Among the various writings by learned men on the subject, Professor Owen's masterly description stands pre-eminent; indeed, he was the only one to solve the riddle, to thoroughly explain the structure of this giant sloth, and to show how its food was obtained.[50] Neither Cuvier, nor the German doctors, nor Mr. Clift had succeeded in so doing.

[50] His views are expounded in his _Memoir on the Megatherium, or Giant Ground Sloth of America_, 1861, which is beautifully illustrated. The Royal Society gave £100 (part of a Government grant of £1000) to enable Professor Owen to carry out this important work.

In the Natural History Museum (Stand O, Gallery No. 2 on plan) is a cast representing the animal nearly erect, and grasping a tree. This magnificent cast (see Plate XVII.) represents an animal eighteen feet in length, and its bones are more massive than those of the elephant. For instance, the thigh-bone is nearly thrice the thickness of the same bone in the largest of existing elephants, the circumference being equal to the entire length. To a comparative anatomist several striking indications of great strength present themselves; thus, not only the very forms of the bones themselves mean strength, but their surfaces, ridges, and crests are everywhere made rough for the firm attachment of powerful muscles and tendons. In the fore part of the body the skeleton is _comparatively_ slender, but the hind quarters show enormous strength and weight combined. The tail, also, is very powerful and massive. The fore limbs are long, and evidently constructed for the exertion of great force. How this force was applied we shall see presently. In both sets of limbs we notice powerful claws, such as might be used for scratching up the ground near the roots of a tree, and it was at one time thought that this was the way in which the creature obtained its leafy food, namely, by digging up trees by the roots and then devouring the leaves. But Professor Owen had another explanation.

As in the living sloths and armadillos (edentata[51]), there are no teeth in the fore part of the jaw. The molar teeth, of which there are five on each side of the upper jaw, and four in the lower, are hollow prismatic cylinders, straight, seven to nine inches long, and implanted in deep sockets. There are no other teeth, but these are composed of different substances, and so arranged that, as the tooth wears, the surface always presents a pair of transverse ridges, thus producing a dental apparatus well suited for grinding up vegetable food. In the elephants, which live on similar food, the grinding is effected by great molar teeth, which are replaced by new ones as the old ones are worn away. In the Megatherium, however, only _one_ set of teeth was provided; but these, by constant upward growth, and continual addition of new matter beneath, lasted as long as the animal lived, and never needed to be renewed.

[51] This word, which means _toothless_, is misleading. All the edentata, however, agree in having no front, or incisor, teeth.

On looking at the model so skilfully set up at South Kensington, and especially at the front part of the skull, it will be seen that the snout and lips must have been somewhat elongated, possibly into a slight proboscis like that of the tapir. The specimens of the lower jaw in the wall-case close by show that it was much prolonged and grooved. This fact must be interpreted to mean that the creature possessed a long and powerful tongue, aided by which it could, like the giraffe, strip off the small branches of the trees which it had broken or bent down within its reach.

A bony shield (or carapace) of a great armadillo was found with one of the specimens described by Mr. Clift, and Buckland and others thought it belonged to the Megatherium; but Owen afterwards showed, by most clear and convincing reasoning from the skeleton, that the Megatherium could not have been protected as armadillos are, by such a shield (see p. 190).

And now we come to the question how it obtained its food. The idea of digging round trees with its claws in order to uproot them, must be partly, if not entirely, given up; for Professor Owen has proved, by a masterly piece of reasoning, that this cumbrous creature, instead of climbing up trees as modern sloths do, actually pulled down the tree bodily, or broke it short off above the ground by a _tour de force_, and, in order to do so, sat up on its huge haunches and tail as on a tripod, while it grasped the trunk in its long powerful arms! Marvellous as this may seem, it can be shown that every detail in its skeleton agrees with the idea. Of course there would be limits to possibilities in this direction, and the larger trees of the period must have been proof against any such Samson-like attempts on the part of the Megatherium; but when the trunk was too big, doubtless it pulled down some of the lower branches. Plate XVIII. is a restoration, by our artist, of the South Kensington skeleton.

Speaking of the extinct sloths of South America, Mr. Darwin thus describes Professor Owen's remarkable discovery: "The habits of these Megatheroid animals were a complete puzzle to naturalists until Professor Owen solved the problem with remarkable ingenuity. Their teeth indicate by their simple structure that these animals ... lived on vegetable food, and probably on the leaves and small twigs of trees; their ponderous forms and great strong curved claws seem so little adapted for locomotion, that some eminent naturalists believed that, like sloths, to which they are intimately related, they subsisted by climbing, back downwards, on trees, and feeding on the leaves. It was a bold, not to say preposterous, idea to conceive even antediluvian trees with branches strong enough to bear animals as large as elephants. Professor Owen, with far more probability, believes that, instead of climbing on trees, they pulled the branches down to them, and tore up the smaller ones by the roots, and so fed on the leaves. The colossal breadth and weight of their hinder quarters, which can hardly be imagined without having been seen, become, on this view, of obvious service instead of being an encumbrance; their apparent clumsiness disappears. With their great tails and huge heels firmly fixed like a tripod in the ground, they could freely exert the full force of their most powerful arms and great claws."[52]

[52] _Journal of Researches._

To this we may add Dean Buckland's description,[53] "His entire frame was an apparatus of colossal mechanism, adapted exactly to the work it had to do; strong and ponderous in proportion as this work was heavy, and calculated to be the vehicle of life and enjoyment to a gigantic race of quadrupeds, which, though they have ceased to be counted among the living inhabitants of our planet, have, in their fossil bones, left behind them imperishable monuments of the consummate skill with which they were constructed. Each limb and fragment of a limb form coordinate parts of a well-adjusted and perfect whole."

[53] _Bridgewater Treatise._

After reading these descriptions, it is not difficult to form a mental picture of the great beast laying siege to a tree, and to conceive the massive frame of the Megatherium convulsed with the mighty wrestling, every vibrating fibre reacting upon its bony attachment with the force of a hundred giants; extraordinary must be the strength and proportions of the tree if, when rocked to and fro, to right and left, in such an embrace, it can long withstand the efforts of its assailant. It yields, the roots fly up, the earth is scattered wide upon the surrounding foliage, and the tree comes down with a thundering crash, cracking and snapping the great boughs like glass. Then the coveted food is within reach, and the giant reaps the reward of his Herculean labours.

Sir Woodbine Parish thought that the Megatherium fed on the Agave, or American aloe.

Another form of extinct sloth found in the same region is the Mylodon. Though of smaller size, it was much bigger than any living sloth, and attained a length of eleven feet. It has the same general structure, but the head and jaws are somewhat different, and more like the recent forms. A nearly perfect and original skeleton of Mylodon gracilis has been set up beside its huge relative's cast in the same gallery at the Natural History Museum. The crowns of its molar teeth are flat instead of being ridged; hence its name, which signified "mill-toothed."

Yet another was the Scelidotherium[54] with its long limbs. Darwin obtained an almost entire skeleton of one of these. It was as large as a polar bear. Speaking of his discovery, he says, "The beds containing the fossil skeletons consist of stratified gravel and reddish mud; a proof that the elevation of the land has been inconsiderable since the great quadrupeds wandered over the surrounding plains, and the external features of the country were then very nearly the same as now. The number of the remains of these quadrupeds embedded in the vast estuary deposits which form the Pampas and cover the granitic rocks of Banda Oriental must be extraordinarily great. I believe a straight line drawn in any direction through the country would cut through some skeleton or bones. As far as I am aware, not one of these animals perished, as was formerly supposed, in the marshes or muddy river-beds of the present land, but their bones have been exposed by the streams intersecting the subaqueous deposit in which they were originally embedded. We may conclude that the whole area of the Pampas is one wide sepulchre of these extinct gigantic quadrupeds."[55]

[54] Greek--_scelis_, limb; _therion_, beast.

[55] _Journal of Researches._

The genus Scelidotherium comprises a number of species and presents characters more or less intermediate between Megatherium and some other genera. The skull is low and elongated, and shows an approach to that of the modern ant-eater. The feet also are different from those of Megatherium (see Fig. 50).

These monster sloths inhabited South America during the latest geological period, known as the Pleistocene. During part of that time North America, as well as Northern Europe and Asia, were invaded by a great ice-sheet, and an arctic climate prevailed. It is therefore very probable that while the mammoth and the mastodon were roaming over North America, giant sloths and armadillos were monarchs of the southern continent. What cause, or causes, led to the extermination of the giant sloths and armadillos is still a matter of speculation. One writer suggests an explanation that seems to deserve consideration. The southern parts of this great continent are even now subject to long-continued droughts, sometimes lasting for three years in succession, and bringing great destruction to cattle. In fact, the discoveries related above were rendered possible by several successive dry seasons. It is argued that the upright position of most of the skeletons found _in situ_ seems to suggest that the creatures must have been mired in adhesive mud sufficiently firm to uphold the ponderous bones after the flesh had decayed. A long drought would bring the creatures from the drained and parched country to the rivers, reduced by want of rain to slender streams running between extensive mud-banks; and it is possible that, in their anxious efforts to reach the water, they may have only sunk deeper and deeper in the mud until they were engulfed. This idea is strengthened by information supplied to Mr. Darwin when in these parts (recorded in his _Journal_). An eye-witness told him that during the _gran seco_, or great drought, the cattle in herds of thousands rushed into the Parana, and, being exhausted by hunger and thirst, were unable to crawl up the muddy banks, and so were drowned.

In the last great drought, from 1830 to 1832, it is probable (according to calculations made) that the number of animals that died was over one million and a half. The borders of all the lakes and streamlets in the province were long afterwards white with their bones.

In the year 1882 reports were published of the discovery of large footprints--supposed to be human--in a certain sandstone near Carson, Nevada, U.S. The locality was the yard of the State prison, and the tracks were uncovered in quarrying stone for building purposes. Many different kinds of tracks were found, some of which were made by an animal allied to the elephant; some resembled those of the horse and deer; others seem to have been made by a wolf, and yet others by large birds. Those supposed to have been made by human giants were in six series, each with alternate right and left tracks. The stride is from two and a half to over three feet, and each footprint is about eighteen inches long. Now, those who believed these tracks to be human must have found it hard to explain how a giant with a foot some eighteen inches long had a stride no longer than that of an ordinary man of to-day, to say nothing of the fact that the straddle was eighteen to nineteen inches! For these and other reasons Professor Marsh has exploded the idea of their having been made by men, and gave good reasons to show that they were probably made by a giant sloth, such as the Mylodon above mentioned, the remains of which have been discovered in the same strata. They agree in size, in stride, and in width between the right and left impressions, very closely with the tracks that a Mylodon would have made, and it seems that those of the fore feet were afterwards impressed by the hind feet, so that each track contains two impressions.

The reader who has some knowledge of natural history will not need to be told that the sloths of the present day, inhabiting the same region as their gigantic ancestors, are of small size, and live among the branches of the trees, together with the spider monkeys, howlers, and other apes. An interesting question to the evolutionist is--How did the change take place from the old huge and heavy types to the smaller and agile types of the present day? Can it be possible that the more difficult and tedious task of pulling down branches and even stems of trees, in order to devour the leaves, was abandoned for the simpler method of climbing up and feeding among the branches? It certainly looks as if a change of this kind had been instituted at some distant period in the past--distant, that is, to _us_, but not very remote geologically. The present method seems so much simpler that we need not be surprised at its adoption, for Nature is ever ready to encourage and assist those among the children of Life which can hit upon and adopt new and improved methods, either in obtaining food or repelling enemies, or other duties imposed upon them. Now, suppose that, in accordance with the well-known fact that variations in the offspring of animals are constantly cropping up, some considerably smaller variety of Megatherium, or Mylodon, or other now extinct type, appeared on the scene, and, by virtue of its comparative agility, could climb a tree and feed among the branches instead of pulling them down: then, as Darwin has so well explained, Nature would seize upon this accidental variation, and give it an advantage over its more awkward relations. Its offspring, too, would inherit the same characteristics, they would adopt the same habits, and, in time, as "natural selection" further increased these characters, by weeding out those that were unfit while fostering all those that were neither large nor clumsy in climbing trees, a new race of sloths would arise. This new race, it can well be imagined, would in time outstrip the old race in numbers, for successful races multiply while unsuccessful ones diminish. Victory is not always to the great and the strong, for cunning and quickness are often of more service than mere brute strength; and perhaps the sloths, as we now see them in the Brazilian forests, have hit upon "a new and original plan" by means of which the old colossal forms described above have been driven out of the field, and so exterminated by a process of competition. Such an explanation would be in thorough harmony with modern teaching, and, as the other suggestion about long-continued droughts, given on p. 184, may not appear satisfactory to some of our readers, we offer this theory for what it may be worth.

A few words about these modern sloths may not be out of place; for we shall better understand how they have succeeded in the struggle for existence when we know something of their manner of life; and in some ways they still resemble their great ancestors.

There are few animals which exhibit in a greater degree what appears to the careless observer to be _deformity_ than the sloth, and none that have, on this account, been more maligned by naturalists. Buffon, and many of the older zoologists, were eloquent upon the supposed defects of the unfortunate sloth. These writers gravely asserted that when the sloth ascends a tree, for the purpose of feeding upon its leaves, it is so lazy that it will not quit its station until every trace of verdure is devoured. Some of them even went so far as to assert that when the sloth was compelled, after thus stripping a tree, to look out for a fresh supply of food, it would not take the trouble to descend the tree, but just allowed itself to drop from a branch to the ground. Even Cuvier, who ought to have known better, echoes this tale, and insinuates that Nature, becoming weary of perfection, "wished to amuse herself by producing something imperfect and grotesque," when the sloths were formed; and he proceeds, with great gravity, to show the "inconvenience of organisation," which, in his opinion, rendered the sloths unfit for the enjoyment of life.

It is quite true that, on the ground, these animals are about the most awkward creatures that can well be imagined. Their fore legs are much longer than their hind ones; all their toes are terminated by very long curved claws, and the general structure of the animal is such as to prevent them from walking in the manner of an ordinary quadruped, for they are compelled to rest on the sides of their hands and feet. Thus they appear the most helpless of animals, and their only means of progression consists in hooking their claws to some inequality in the ground, and thus dragging their bodies painfully along. But in their natural home, amongst the branches of trees, all these seeming disadvantages vanish--nay, the very peculiarities of structure which render the sloths objects of pity on the ground, are found to render them admirably adapted to their peculiar mode of life. The sloth is a small animal, rarely more than two feet in length, and covered with woolly hair--probably a protection against snakes, its only enemies. It spends nearly the whole of its life in the trees. There, safe from the prowling animals on the ground below, it hangs like a hammock from the bough, and even travels along the branches with its body downwards, using its long claws like grappling-irons.

It looks slothful enough when asleep, for then it resembles a bunch of rough hair, and a jumble of limbs close together, hanging to a branch; but when awake it is industrious in its search for nice twigs and leaves, and moves along with considerable activity. When the atmosphere is still, the sloth keeps to its tree, feeding on the leaves and twigs, but when there is wind, and the branches of neighbouring trees come in contact, the opportunity is seized, and the animal moves along the forest under the shady cover of the boughs. The Indians have a saying that "when the wind blows the sloth begins to crawl;" and the reason is quite evident, for they cannot jump, but can hang, swing, and crawl suspended.

We now pass on to the old gigantic representative of the armadillo, the Glyptodon.[56] To the eye it resembles more or less an armadillo, and has a huge cuirass, or large plate of armour, covering the whole of the body, but allowing the head to show in front, while the legs come out beneath. Both head and tail were also protected with armour. The great shield, or carapace, in most of the extinct armadillos, is composed of long plates of regular shape, closely united at their edges (sutures) so as to form a solid piece. It is evident, therefore, that this creature, having no movable bands, as living armadillos have, could not roll itself up into a ball. The fore feet have thick, short toes, instead of long ones, such as their modern representatives have; and from this we may infer that they were not in the habit of burrowing or of seeking their food underground. The family of Glyptodonts seem to have been chiefly confined to the continent of South America, but some species are known to have extended their range as far as Mexico, and Texas into North America. A good deal of confusion has arisen with regard to the classification of these old-fashioned armadillos, on account of the fact that isolated specimens of their tails have often been found, and these cannot always be referred to the right carapaces. For example, it should be pointed out here that the tail represented in Fig. 51 really belongs to another genus, known as Hoplophorus.[57]

[56] So named by Sir R. Owen, in reference to the sculptured aspect of the grinding surface of the teeth. Greek--_glupho_, I carve; _odous, odontos_, tooth.

[57] Greek--_Hoplon_, armour; _phero_, I bear.

In Glyptodon asper (Plate XIX.), the scutes of the carapace had a beautiful rosette-like sculpture, while the sheath of the tail was entirely composed of a series of movable rings, ornamented with large projecting tubercles. The vertebræ of the backbone are almost entirely fused together into a long tube, and also are joined to the under surface of the great shield, to which the ribs are united. The cheek-teeth are sixteen in number, four above and four below on each side. These are channelled with two broad and deep grooves, which divide the surface into three distinct lobes. Hence the name of the animal.

The tessellated carapace of the Glyptodon was at first thought to belong to the Megatherium, with which the remains were associated, but Professor Owen clearly demonstrated the impossibility of this idea.

Fig. 51 represents Glyptodon clavipes (Owen) from the Pleistocene deposits of Buenos Ayres; but the reader will gain a much better idea of the animal by inspecting the splendid specimen of Glyptodon asper in the Natural History Museum, near the centre window at the east end of the Pavilion (Glass-case Q on plan).

Plate XIX. is a restoration of another species by our artist.[58]

[58] This plate is based on a beautiful drawing in a Spanish work, _Anales del Museo publico Buenos Aires_. G. Burmeister, M.D., Phil. D. Tomo Segundo.

In the Museum of the Royal College of Surgeons (which the reader is recommended to visit) there are several most valuable specimens of these extinct armadillos from South America.

Armadillos belong, with sloths and ant-eaters, to the same family of so-called toothless animals (edentata) with no front teeth, though one or two forms really are toothless. Those of the present day have their bony armour divided up into a series of bands, so that they can roll themselves up, more or less, into balls. They burrow under the ground, where they get their food to a certain extent, and live a safe life, protected by their casque of mail. Their only enemies seem to be the monkeys, and one of the tricks of the young monkeys in the American forests is, when they find an armadillo away from home, to pull its tail unmercifully, and try to drag it about. Snakes cannot hurt them. Mr. Hudson, in his most interesting book, _A Naturalist in La Plata_, narrates how he watched an armadillo kill a snake and then devour it.

If we examine the anatomy of the armadillo, we shall find that its bones greatly resemble those of the sloth, but still there are a few differences. It is a burrowing animal, and therefore requires great power of scratching and tearing the ground. Why the colossal forms of armadillo should have become extinct and only small ones survived to the present time, is one of the many and perplexing problems presented by the study of extinct animals. One would have thought from its size and strength that the Glyptodon had been built, like Rome, for eternity.