megatherium

Megatherium Fossil range: 2–0.008 Ma PreЄ Є O S D C P T J K Pg N ↓ Late Pliocene to Early Holocene
Skeleton of Megatherium americanum in the Natural History Museum, London
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Superorder:	Xenarthra
Order:	Pilosa
Family:	†Megatheriidae
Genus:	†Megatherium Cuvier, 1796
Type species
†Megatherium americanum Cuvier, G., 1796
Species
†M. altiplanicum Saint-André & de Iuliis, 2001 †M. tarijense Gervais & Ameghino, 1880 †M. medinae Philippi, 1893 †M. istilarti Kraglievich, 1925 †M. parodii Hoffstetter, 1949 †M. sundti Philippi, 1893 †M. gallardoi Ameghino & Kraglievich, 1921

Megatherium ("Great Beast") was a genus of elephant-sized ground sloths endemic to Central America and South America that lived from the Pliocene through Pleistocene existing approximately 5.289 million years.^[1]

The rhinoceros-sized Promegatherium is suggested to be the ancestor of Megatherium.

Characteristics

Illustration 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 it was 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. Megatherium species were members 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^[2] indicates 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.

Megatherium americanum skeleton, Muséum national d'Histoire naturelle, Paris

There is a common misbelief that the sabre-toothed cat Smilodon hunted Megatherium, but healthy adult sloths were far too large for Smilodon 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.^[3] 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.

Habitat

They inhabited woodlands and grasslands.

Distribution

Megatherium was endemic to South America.^[4] The most modern descendants of Megatherium were extant in parts of South America until at least as recently as circa 10,000 years ago. An example of these most recent finds is at Cueva del Milodon in Patagonian Chile.^[5]

Habits

Hips, hind legs, and tail of Megatherium americanum

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

While it is generally believed to have been mostly, if not exclusively, vegetarian, it has been suggested that it may have used its size and strength to take over the kills of Smilodon and to scavenge or hunt Glyptodon.

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

Megatherium americanum skeleton seen from below

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.

It has been suggested that the giant sloth may have been a carnivore, although this is a controversial claim.^[6]

Evolution

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.^{[verification needed]} In the south, the giant ground sloth flourished until about 10,000 years ago. Most cite the appearance of an expanding population of human hunters as the cause of its extinction.

The oldest (and smallest) species of Megatherium is M. altiplanicum of Pliocene Bolivia.^[7] 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 culture

• In Jules Verne's Journey to the Center of the Earth, the men meet a giant ground sloth.
• In H. G. Wells' The Time Machine, while in the distant future, the Time Traveller comes across a giant skeleton in the ruins of a museum and likens it to a Megatherium.
• In The Simpsons episode Treehouse of Horror V, Homer runs into a giant ground sloth.
• In the classic PC game Time Commando, a Megatherium is the final boss in the Prehistoric level that has to be defeated in order to pass to the Roman Empire level.
• In the cartoon The Tick, a giant ground sloth crashes into the Tick's tent and kidnaps his sidekick, Arthur.
• A Megatherium can be seen in the BBC documentary Walking with Beasts, where it is depicted as both a herbivore and a scavenger. It is also depicted as an omnivore in the Animal Planet special Giant Monsters.
• In another BBC documentary, Prehistoric America, the Megatherium is depicted as a herbivore.
• The Ice Age series of films features a character named Sid who is apparently a Megatherium. However, Sid simply calls himself a sloth and neither he nor any others of his kind shown in the films appear to be taller than six feet.
• In the 1937 version of "Lost Horizon" the character of Alexander P. Lovett is excited over a fossil of the lumbar of a Megatherium, that he found in Asia.

References

Notes

External links

Wikimedia Commons has media related to: Megatherium

• Paleocraft Megatherium
• BBC - Walking With Beasts - Megatherium
• "According to locals, slothlike monster roams Amazon". Dallas News. 2007-07-28. http://www.dallasnews.com/sharedcontent/dws/news/world/stories/072907dnnewsamazon.51899eb.html. 

See also

• Megatherium Club
• Mapinguari

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