Megatherium

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Megatherium
Fossil range: Late Pliocene to Early Holocene

Illustration of Megatherium.

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 that lived from 2 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.

1 Characteristics
2 Distribution
3 Habits
4 Diet and feeding habits
5 Evolution
6 Megatherium In Popular Culture
7 Gallery
8 See also
9 References
10 External links

[edit] Characteristics

Skeleton of Megatherium americanum.

Unlike its living relative, the tree sloth, Megatherium was one of the largest mammals to walk the Earth, weighing 5 tons, about as much as an African bull elephant. Although mainly a quadruped (walked on four legs), 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, had to walk on the sides of its feet because huge claws prevented it from putting them flat on the ground. The Megatherium species was a member of the abundant Pleistocene megafauna - a wide variety of very 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 and specially adapted body made it possible to feed at heights otherwise unreachable by other contemporary herbivores. Rising on its powerful hind legs and using its tail to form a tripod, Megatherium was able to support its massive body weight while using the curved claws on its long forelegs to pull down branches with the choicest leaves. Its large deep jaw is believed to have housed a long tongue, as in the modern tree sloth, which it would then use to pull leaves into its mouth.

Some recent morpho-functional analysis (Bargo, 2001) indicate that M. americanum was well adapted for strong and mainly vertical biting. The teeth are extremely hypsodont and bilophodont, and the sagittal section of each loph is triangular with a sharp edge. This suggests that the teeth were used mainly for cutting, rather than grinding, and that hard and fibrous food was not the main dietary component.

There is a common misbelief that the sabre-toothed cat Smilodon hunted Megatherium, but healthy adult sloths were far too big for even 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 aggressively, like daggers (Fariña and Blanco, 1996). The conclusion is that due to its nutrient-poor habitats, Megatherium may have actually taken over the kills of Smilodon. A number of adult Glyptodon fossils have also been found where the shell was turned upside down. 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.

[edit] Distribution

Megatherium was endemic to South America (McKenna and Bell, 1997).

[edit] Habits

Illustration of Megatherium from around 1920.

Little is known about the giant ground sloth. It may have used its tremendous 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 mainly on plants that grew on the ground.

It is believed that the giant sloth lived in groups, but it may have lived singly in caves. According to the theory of the social giant sloth, the groups consisted of two males and seven females. At any given time, up to four female sloths would be pregnant or nursing, while the remaining three tended to the hunting and gathering for the menfolk. It is also believed that it lived in a woodland and grassy environments.

[edit] 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 is 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.

[edit] 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. Some cite the appearance of human hunters as the cause of its extinction, others climatic changes; however, the actual cause is unknown.

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.

When the ancestors of the giant ground sloth became established in South America, the land bridge joining North and South America was submerged. The sloth and other edentates (simple toothed creatures) developed undisturbed and were unique to this part of the world. The edentate families looked very different but had certain things in common: Simple teeth and different numbers of vertebrae to provide varying degrees of spinal movement. Nearly six million years passed before the land dividing the continents appeared again. Some sloths and other edentates then moved further north and became widespread before they disappeared completely. 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 changes, however the actual cause is unknown.

[edit] Megatherium In Popular Culture

In Jules Verne's Journey to the Center of the Earth, the characters encounter a giant ground sloth.

In the 2003 Animal Planet series, Giant Monsters, Jeff Corwin sees a Megatherium fighting a Smilodon.

In the BBC documentary Walking with Beasts, Megatherium appears in Episode 5. It kills a Smilodon and is shown scavenging in the documentary.

In the Simpsons Treehouse of Horror V episode, Time and Punishment, Homer Simpson goes back in time to what appears to be the Late Cretaceous and encounters a giant sloth.