Megatherium (/mɛɡəˈθɪəriəm/ meg-ə-THEER-ee-əm; from Greek méga (μέγα) 'great' + theríon (θηρίον) 'beast') is an extinct genus of ground sloths endemic to South America that lived from the Early Pliocene[1] through the end of the Late Pleistocene.

Various other species belonging to the subgenus Pseudomegatherium ranging in size comparable to considerably smaller than M. americanum are known from the Andean region.

The specimen was then shipped to Spain the following year wherein it caught the attention of the French paleontologist Georges Cuvier, who named the animal in 1796 and was the first to determine, by means of comparative anatomy, that Megatherium was a giant sloth.

Megatherium americanum is thought to have been a browser that fed on the foliage and twigs of trees and shrubs using a black rhinoceros–like prehensile upper lip.

Despite its large body size, Megatherium americanum is widely thought to have been able to adopt a bipedal posture at least while standing, which allowed it to feed on high-growing leaves, as well as possibly to use its claws for defense.

On the orders of the then viceroy of la Plata, Nicolás Cristóbal del Campo, Marqués de Loreto, the specimen was moved to the capital Buenos Aires.

[4] At the direction of the cabinets main taxidermist Juan Bautista Bru, the specimen was then mounted for public exhibition (which remains unaltered in the modern museum display).

Cuvier later wrote a fuller description in 1804, which was republished in his famous 1812 book Recherches sur les ossemens fossiles de quadrupèdes.

Cuvier identified Megatherium as a sloth primarily on the basis of its skull morphology, the dental formula and the shoulder, while regarding the anatomy of its limbs as more similar to armadillos and anteaters.

In 1888 Argentine explorer Francisco Moreno erected the species Megatherium filholi for remains found in the Late Pleistocene of Argentina.

[13][14][15] In 1880 Paul Gervais and Florentino Ameghino described the species M. tarijense from remains of Pleistocene age found in Bolivia.

In 1893 Rodolfo Amando Philippi erected the species M. sundti and M. medinae from remains found in the Pleistocene of Bolivia and Chile, respectively.

[16][17] In 1921, Florentino's brother Carlos Ameghino and Lucas Kraglievich described the species Megatherium gallardoi based on remains found in the Pampas of Northern Argentina, of Early-Middle Pleistocene age.

Taxonomy according to Pujos (2006) and De Iuliis et al (2009):[22][23] Megatherium gallardoi Ameghino & Kraglievich, 1921 from the Pampas dating to the Early to Middle Pleistocene[15] has sometimes been regarded as a synonym of M.

[19] The species Megatherium filholi Moreno, 1888 also from the Pleistocene of the Pampas region, historically regarded to be a junior synonym of M. americanum representing juvenile individuals has been suggested to be valid by some recent authors.

[24] The subfamily to which Megatherium belongs, Megatheriinae, first appeared in the Middle Miocene in Patagonia, at least 12 million years ago, represented by the genus Megathericulus.

[25] The earliest known remains of the genus Megatherium are known from the Pliocene, found in Bolivia (M. altiplanicum) and the Pampas (indeterminate species), dating to at least 3.6 million years ago.

[33] In many species of Megatherium, the lower jaw is relatively deep, which served to accommodate the very long hypselodont (evergrowing) teeth,[20] which are considerably proportionally longer than those of other ground sloths.

[34] The skull of M. americanum has a relatively narrow snout/muzzle with a ossified nasal septum, and is suggested to have had a thick prehensile upper lip, similar to that of the living black rhinoceros, which compensated for the lack of teeth at the front of the jaws.

[49] Due to its very large body size, some authors have alternatively argued that Megatherium americanum was probably hairless like modern elephants for thermodynamic reasons.

[50] However this has been disputed, with other authors suggesting based on thermodynamic modelling assuming a living xenarthran-like metabolism that Megatherium species probably had a dense coat of fur around 3 centimetres (1.2 in) thick to be able to tolerate the relatively cool environments they inhabited.

[49] Based on fossil trackways and the anatomy of its inner ear, which is considerably different from living sloths and more similar to those of armadillos, species of Megatherium, while probably not capable of moving at considerable speed due to limitations of their skeletal anatomy (with one study estimating a max speed of approximately 2.2 metres per second (7.2 ft/s) or 7.92 kilometres per hour (4.92 mph), a fraction of the 5–6 metres per second (16–20 ft/s) or 18–21.6 kilometres per hour (11.2–13.4 mph) top speed observed for living elephants[49]) were likely significantly more agile and mobile than living sloths, which are only capable of moving 0.5–0.6 kilometres per hour (0.31–0.37 mph).

[52] The anatomy of its forelimb bones suggests that M. americanum had the ability to rapidly and powerfully extend its arms, which likely made its claws effective stabbing weapons.

[3] Megatherium disappeared simultaneously along with the vast majority (>80%) of other large (megafaunal) South American mammals, as part of the end-Pleistocene extinction event.

[59] At the Paso Otero 5 site in the Pampas of northeast Argentina, Fishtail points are associated with burned bones of Megatherium americanum and other extinct megafauna.

[59] The Megatherium Club, named for the extinct animal and founded by William Stimpson, was a group of Washington, D.C.–based scientists who were attracted to that city by the Smithsonian Institution's rapidly growing collection, from 1857 to 1866.