Scientific name: Megatherium americanum Scientific classification: Phylum: Chordata Class: Mammalia Order: Pilosa Family: Megatheriidae When did it become extinct? The last giant ground sloths are thought to have died out around 8,000 to 10,000 years ago. Where did it live? The giant ground sloths were found throughout South America.
South America is probably the most biodiverse landmass on earth, yet, many thousands of years ago, the fauna of this continent was even more remarkable. A perfect example of this long-gone South American fauna is a ground-dwelling sloth that was the same size as an elephant. This was the giant ground sloth, and it was an immense and unusual animal. Fully grown, the giant ground sloth was about 6 m long, and estimates of its weight range between 4 and 5 tonnes. Several skeletons (real and copies) of this animal are to be found in museum collections around the world, and one of the most astonishing things about these remains is the size of the bones. The limb bones and their supporting structures are massive and give an impression of a heavy, powerful animal. In life, the digits of the animal were tipped with long claws, which may have been used to grab plant food or even as weapons.
We know from the skeletons of this animal that the bones of the hind feet were arranged in a very peculiar way, making it impossible for the living animal to place its feet flat on the ground. The animal could certainly rear up onto its hind legs, and perhaps even manage to amble around in this posture, using its thick tail as a strong prop, but it had to shuffle around on the outside of its feet with the long claws pointing inward. The giant ground sloth may have been able to make better progress on all fours, possibly reserving its two-legged stance for feeding or defense.
As the giant ground sloth is related to the living sloths, it was always assumed that they were gentle plant-eating animals, but some recent, controversial scientific research has shed some light on how this massive beast used its forelimbs. These studies suggest the forelimbs of a giant ground sloth were adapted for fast movement. Such an ability was of little use to a plant-nibbling animal that needed a strong, sustained pull to bring tasty leaf-bearing branches within reach of its mouth. The research suggest that the muscles of the forelimbs were used to power the large claws into other animals, and maybe not only in defense. The animal's teeth also give intriguing insights into the way it fed. They are not the normal grinding blocks that are found in the mouths of plant-feeding mammals. They and the jaws they sit in appear to be adapted for slicing, much like the jaws and teeth of meat-eating animals. The claws and teeth of this giant mammal have led some people to suggest that the giant ground sloth was not a plant feeder at all, but a scavenging animal that used its size to drive predatory animals from their kill before digging in to the carcass. The image of a 5-tonne brute ambling over to a group of dire wolves, scaring them off, and then devouring their kill is quite fantastic. Regardless of this research, it is decidedly unlikely that this giant lived in this way, and like its living relatives, the giant ground sloth was probably a herbivore, but it may have been able to use its forelimbs and teeth to defend itself.
As with almost all of the long-dead animals that once roamed South America, we cannot be certain what brought about the demise of the giant ground sloth. It has been speculated that the arrival of modern humans, with spears and arrows, led to their extinction, but it is reasonable to assume that there was something much more far-reaching happening at the time that wiped these animals out. Climate change is one of the usual suspects, and we know that the earth's habitats were going through some massive changes at the time these animals went extinct. Global temperatures were changing, and land-dwelling animals everywhere were being affected. Hunting may have had an effect, but it may have been minor compared to the ravages of climate change.
Today, there are still vast areas of South America where people rarely venture, and some people believe that a species of giant ground sloth may have somehow survived the events that wiped out its relatives and is alive and well in these remote areas. Local inhabitants call the beast the mapinguary, and it is said to rear up on its back legs and emit a foul-smelling odor from a gland in its abdomen—not only that, but the creature is said to be impervious to bullets and arrows, thanks to some very tough skin on its belly and back. Without a specimen or an excellent photograph, it is difficult to take these stories seriously, but it is worth remembering that previously unknown species of mammal are discovered fairly regu larly, and some of them are surprisingly large. If a live giant ground sloth was found today, it would be the zoological story of all time.
♦ It is thought that there were around four species of giant ground sloth. The species mentioned here (Megatherium americanum) was by far the biggest. The closest living relatives of these extinct animals are the anteaters, armadillos, and tree sloths. The biggest of these, the giant anteater, would be dwarfed by even the smallest giant ground sloth.
♦ In 1895, a rancher by the name of Eberhardt found some hide in a cave in Patagonia that turned out to be giant ground sloth skin. The skin was in very good condition, and some people believed that it was from an animal that died relatively recently. When techniques became available to age the skin, it was found to be several thousand years old—it was just that the very dry conditions in the cave had prevented it from rotting. Interestingly, the mummified skin was studded with bony nodules, which probably gave the animal excellent protection from the teeth and claws of predators, and perhaps even the spears and arrows of early humans.
♦ It would be fantastic if a species of giant ground sloth had somehow survived into the modern day, but accounts of the mapinguary may be due to confusion with other animals or derived from folk memories of when humans encountered these animals thousands of years ago.
Further Reading: Bargo, M. S., G. De Iuliis, and S. F. Vizcaíno. "Hypsodonty in Pleistocene Ground Sloths." Acta Palaeontologica Polonica 51 (2006): 53-61; Bargo, M. S., N. Toledo, and S. F. Vizcaíno. "Muzzle of South American Pleistocene Ground Sloths (Xenarthra, Tardigrada)." Journal of Morphology 267 (2006): 248-63; Bargo, M. S. "The Ground Sloth Megatherium americanum: Skull Shape, Bite Forces, and Diet." Acta Palaeontologica Polonica 46 (2001): 173-92; Fariña, R. A., and R. E. Blanco. "Megatherium, the stabber." Proceedings of the Royal Society of London 263 (1996): 1725-29.
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