megatherium [Gr.=large beast], extinct ground sloth, of the genus Megatherium, that was widely distributed in North and South America in the Pleistocene epoch. Fossil evidence shows that these mammals became extinct comparatively recently, about the time that the first explorers reached the New World. A huge beast, the megatherium attained a length of 18 ft (5.5 m) and probably weighed several tons. The hind legs and tail were massive, the forelegs slender and supple; the animal probably supported itself much of the time in a semierect position on its hind legs and tail and used its forelegs to pull from trees the foliage on which it fed. The megatherium is classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Edentata, family Megatheriidae.
Megatherium ("Great Beast") was a genus of elephant-sized ground sloths that lived from two million to 8,000 years ago. A related genus was Nothrotheriops, which were primarily bear-sized ground sloths. The rhinoceros-sized Promegatherium is suggested to be the ancestor of Megatherium.


Unlike its living relatives, the tree sloths, Megatherium was one of the largest mammals to walk the Earth, weighing five tons, about as much as an African bull elephant. Although primarily a quadruped, its footprints show that it was capable of assuming a bipedal stance. When it stood on its hind legs, it was about twice the height of an elephant, or about twenty feet tall. This sloth, like a modern anteater, walked on the sides of its feet because its claws prevented it from putting them flat on the ground. The Megatherium species was a member of the abundant Pleistocene megafauna, large mammals that lived during the Pleistocene epoch.

Megatherium had a robust skeleton with a large pelvic girdle and a broad muscular tail. Its large size enabled it to feed at heights unreachable by other contemporary herbivores. Rising on its powerful hind legs and using its tail to form a tripod, Megatherium could support its massive body weight while using the curved claws on its long forelegs to pull down branches with the choicest leaves. Its jaw is believed to have housed a long tongue, which it would then use to pull leaves into its mouth, similar to the modern tree sloth.

Some recent morpho-functional analysis indicate that M. americanum was adapted for strong vertical biting. The teeth are hypsodont and bilophodont, and the sagittal section of each loph is triangular with a sharp edge. This suggests the teeth were used for cutting, rather than grinding, and that hard fibrous food was not the primary dietary component. There is a common misbelief that the sabre-toothed cat Smilodon hunted Megatherium, but healthy adult sloths were far too large for this large cat to attack. Richard Fariña and Ernesto Blanco of the Universidad de la República in Montevideo have analysed a fossil skeleton of M. americanum and discovered that its olecranon--the part of the elbow to which the triceps muscle attaches--was very short. This adaptation is found in carnivores and optimises speed rather than strength. The researchers say this would have enabled M. americanum to use its claws like daggers. The conclusion is that due to its nutrient-poor habitats, Megatherium may have taken over the kills of Smilodon. A number of adult Glyptodon fossils exist in which the creatures died on their backs. This hints at Megatherium scavenging or hunting this animal, as no other known animal existed in South America during that period that could flip an adult Glyptodon.


Megatherium was endemic to South America .


Little is known about the giant ground sloth. It may have used its size and strength to take over the kills of Smilodon and to scavenge or hunt Glyptodon (see "Characteristics" section above) while its very thick skin, which was covered with dense, heavy fur, protected it from predators.

It was a herbivorous animal and, although it could stand on its hind legs, using its tail as a balancing tripod, to reach for vegetation, the giant ground sloth fed chiefly on terrestrial plants.

It is thought that the giant sloth lived in groups, but it may have lived singly in caves. It is also believed that it lived in woodland and grassland environments.

Diet and feeding habits

The giant ground sloth lived in the lightly wooded areas of South America, feeding on the leaves such as yuccas, agaves, and grasses. The closely related genus Eremotherium lived in more tropical environments further north, and in North America. Pulling itself upright to sit on its haunches or to stand, the giant ground sloth balanced its weight with its tail. It then tugged at plants with its feet, digging them up with the five sharp claws on each foot. The sloth used its simple teeth to grind down food before swallowing it, and its highly developed cheek muscles helped in this process. The sloth's stomach was able to digest coarse and fibrous food. For millions of years, the sloth had no enemies to bother it, so it was probably a diurnal feeder. It is likely that it spent a lot of time resting to aid digestion.


The ground sloths, as with all other xenarthrans, evolved in isolation in South America, while it was an island during the Paleogene. During the Pliocene, the Central American Isthmus formed, causing the Great American Interchange, and a mass extinction of much of the indigenous South American megafauna. Ground sloths were largely unaffected and continued to thrive in spite of competition from the northern immigrants. In fact, ground sloths were among the various South American animal groups to migrate northwards, into North America, where they remained and flourished until the late Pleistocene. In the south, the giant ground sloth flourished until about 10,000 years ago. Some cite the appearance of human hunters as the cause of its extinction, others climatic change.

The oldest (and smallest) species of Megatherium is M. altiplanicum of Pliocene Bolivia. It was very similar to the Miocene ground sloth, Promegatherium, and was about the size of a rhinoceros. Species of Megatherium became larger and larger, with the largest species, M. americanum of the late Pleistocene, reaching the size of an African Elephant.

Megatherium In Popular Culture

See also


  • (2001) The ground sloth Megatherium americanum: Skull shape, bite forces, and diet. Acta Palaeontologica Polonica, 46(2): 173–192.
  • Fariña, R. A.; R. E. Blanco (1996). "Megatherium, the stabber". Proceedings of the Royal Society of London 263 1725–1729.
  • McKenna, M. C, and S. K. Bell. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp.
  • (2001) The smallest and most ancient representative of the genus Megatherium Cuvier, 1796 (Xenarthra, Tardigrada, Megatheriidae), from the Pliocene of the Bolivian Altiplano. Geodiversitas, 23(4): 625-645.

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