The vertebræ of the neck (as exhibited in the foreshortened figure ([Fig. 186]), taken from the work of Pander and D’Alton, and showing nearly a front view of the head), as well as the anterior and posterior extremities of the Madrid skeleton, although powerful, are not to be compared in dimensions to those of the other extremity of the body; for the head seems to have been relatively light and defenceless. The lumbar vertebræ increase in a degree corresponding to the enormous enlargement of the pelvis and the posterior members. The vertebræ of the tail are enormous, as is seen in [Fig. 187], which represents the bones of the pelvis and hind foot, discovered by Sir Woodbine Parish, and now in the Museum of the College of Surgeons. If we add to these osseous organs the muscles, tendons, and integuments which covered them, we must admit that the tail of the Megatherium could not be less than two feet in diameter. It is probable that, like the Armadillo, it employed the tail to assist in supporting the enormous weight of its body; it would also be a formidable defensive organ when employed, as is the case with the Pangolins and Crocodiles. The fore-feet would be about three feet long and one foot broad. They would form a powerful implement for excavating the earth, to the greatest depths at which the roots of vegetables penetrate. The fore-feet rested on the ground to their full length. Thus solidly supported by the two hind-feet and the tail, and in advance by one of the fore-feet, the animal could employ the fore-foot left at liberty in clearing away the earth, in digging up the roots of trees, or in tearing down the branches; the toes of the fore-feet were, for this purpose, furnished with large and powerful claws, which lie at an oblique angle relatively to the ground, much like the burrowing talons of the mole.
Fig. 187.—Bones of the pelvis of the Megatherium.
The solidity and size of the pelvis must have been enormous; its immense iliac bones are nearly at right angles with the vertebral column; their external edges are distant more than a yard and a half from each other when the animal is standing. The femur is three times the thickness of the thigh-bone of the Elephant, and the many peculiarities of structure in this bone appear to have been intended to give solidity to the whole frame, by means of its short and massive proportions. The two bones of the leg are, like the femur, short, thick, and solid; presenting proportions which we only meet with in the Armadilloes and Anteaters; burrowing animals with which, as we have said, its two extremities seem to connect it.
The anatomical organisation of these members denotes heavy, slow, and powerful locomotion, but solid and admirable combinations for supporting the weight of an enormous sedentary creature; a sort of excavating machine, slow of motion but of incalculable power for its own purposes. In short, the Megatherium exceeded in dimensions all existing Edentates. It had the head and shoulders of the Sloth, the feet and legs combined the characteristics of the Anteaters and Sloths, of enormous size, since it was at least twelve feet long when full grown, its feet armed with gigantic claws, and its tail at once a means of supporting its huge body and an instrument of defence. An animal built with such massive proportions could evidently neither creep nor run; its walk would be excessively slow. But what necessity was there for rapid movement in a being only occupied in burrowing under the earth, seeking for roots, and which would consequently rarely change its place? What need had it of agility to fly from its enemies, when it could overthrow the Crocodile with a sweep of its tail? Secure from the attacks of other animals, this robust herbivorous creature, of which [Figure 188] is a restoration, must have lived peacefully and respected in the solitary pampas of America.
Fig. 188.—Megatherium restored.
The immediate cause of the extinction of the Megatherium is, probably, to be found in causes which are still in operation in South America. The period between the years 1827 and 1830 is called the “gran seco,” or the great drought, in South America; and according to Darwin, the loss of cattle in the province of Buenos Ayres alone was calculated at 1,000,000 head. One proprietor at San Pedro, in the middle of the finest pasture-country, had lost 20,000 cattle previously to those years. “I was informed by an eyewitness,” he adds, “that the cattle, in herds of thousands, rushed into the Parana, and, being exhausted by hunger, they were unable to crawl up the muddy banks, and thus were drowned. The arm of the river which runs by San Pedro was so full of putrid carcases, that the master of a vessel told me that the smell rendered it quite impassable. All the small rivers became highly saline, and this caused the death of vast numbers in particular spots; for when an animal drinks of such water it does not recover. Azara describes the fury of the wild horses on a similar occasion: rushing into the marshes, those which arrived first being overwhelmed and crushed by those which followed.”[100] The upright position in which the various specimens of Megatheria were found indicates some such cause of death; as if the ponderous animal, approaching the banks of the river, when shrunk within its banks, had been bogged in soft mud, sufficiently adhesive to hold it there till it perished.