Megatherium

Megatherium (/mɛɡəˈθɪəriəm/ meg-ə-THEER-ee-əm from the Greek mega , meaning 'great', and therion , 'beast') was a genus of elephant-sized ground sloths endemic to South America, sometimes called the giant ground sloth, that lived from the Early Pliocene through the end of the Pleistocene. Only a few other land mammals equaled or exceeded Megatherium in size, such as large proboscideans (e.g., elephants) and the giant rhinoceros Paraceratherium. Megatherium was first discovered in 1788 on the bank of the Luján River in Argentina, the holotype specimen was then shipped to Spain the following year wherein it caught the attention of the esteemed paleontologist Georges Cuvier, Cuvier was the first to determine, by means of comparative anatomy, that Megatherium was a sloth. The first fossil specimen of Megatherium was discovered in 1788 by Manuel Torres, on the bank of the Luján River in Argentina. The fossil was shipped to Museo Nacional de Ciencias Naturales in Madrid the following year, where it remains. It was reassembled by museum employee Juan Bautista Bru, who also drew the skeleton and some individual bones. Based on Bru's illustrations, comparative anatomist Georges Cuvier determined the relationships and appearance of Megatherium. He published his first paper on the subject in 1796, a transcript of a previous lecture at the French Academy of Sciences. He published on the subject again in 1804; this paper was republished in his book Recherches sur les ossemens fossiles de quadrupèdes. In his 1796 paper, Cuvier assigned the fossil the scientific name Megatherium americanum. Cuvier determined that Megatherium was a sloth, and at first believed that it used its large claws for climbing trees, like modern sloths, although he later changed his hypothesis to support a subterranean lifestyle, with the claws used to dig tunnels. Fossils of Megatherium and other western megafauna proved popular with the Georgian era public until the discovery of the dinosaurs some decades later. Since the original discovery, numerous other fossil Megatherium skeletons have been discovered across South America, in Argentina, Bolivia, Brazil, Chile, Colombia (Quipile, Cundinamarca), Guyana, Paraguay, Peru and Uruguay. New species in the genus Megatherium, M. urbinai and M. celendinense, have been described in 2004 and 2006 respectively. M. celedinense is named after Celendin, Cajamarca Province in the Peruvian Andes. Ground sloths belong to superorder Xenarthra, a group of South American origin which also includes extinct pampatheres and glyptodonts, as well as living tree sloths, armadillos and anteaters. The subgenus and species Megatherium (Pseudomegatherium) tarijense appears to be a junior synonym of M. americanum, and merely a small individual. The ground sloths, as with all other xenarthrans, evolved in isolation in South America, while it was an island continent 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. 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.