genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

ground sloth Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. The term is used to refer to all extinct sloths because of the large size of the earliest forms discovered, compared to existing tree sloths. The Caribb ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 through the end of the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

. It is best known for the

elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantida ...

-sized

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specim ...

''M. americanum'', sometimes called the giant ground sloth, or the megathere, native to the

Pampas The Pampas (from the qu, pampa, meaning "plain") are fertile South American low grasslands that cover more than and include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, Entre Ríos, and Córdoba; all of Uruguay; and Brazi ...

through southern

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

during the Pleistocene. Various other smaller species belonging to the subgenus ''Pseudomegatherium'' are known from the Andes. ''Megatherium'' is part of the sloth family

Megatheriidae Megatheriidae is a family of extinct ground sloths that lived from approximately 23 mya—11,000 years ago. Megatheriids appeared during the Late Oligocene (Deseadan in the SALMA classification), some 29 million years ago, in South America ...

, which also includes the similarly giant ''

Eremotherium ''Eremotherium'' (from Greek for "steppe" or "desert beast": ἔρημος "steppe or desert" and θηρίον "beast") is an extinct genus of giant ground sloth, in the family Megatheriidae, the largest and most heavily built family of sloths. ' ...

'', comparable in size to ''M. americanum,'' which was native to tropical South America, Central America and North America as far north as the southern United States. Only a few other land

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s equaled or exceeded ''M. americanum'' in size, such as large proboscideans (e.g., elephants) and the giant rhinoceros ''

Paraceratherium ''Paraceratherium'' is an extinct genus of hornless rhinoceros. It is one of the largest terrestrial mammals that has existed and lived from the early to late Oligocene epoch (34–23 million years ago). The first fossils were discovered ...

''. ''Megatherium'' was first discovered in 1788 on the bank of the Luján River in Argentina. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

specimen was then shipped to

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...

the following year wherein it caught the attention of the paleontologist Georges Cuvier, who was the first to determine, by means of comparative anatomy, that ''Megatherium'' was a sloth. ''Megatherium'' became extinct around 12,000 years ago during the

Quaternary extinction The Quaternary period (from 2.588 ± 0.005 million years ago to the present) has seen the extinctions of numerous predominantly megafaunal species, which have resulted in a collapse in faunal density and diversity and the extinction of key ecol ...

event, which also claimed most other large mammals in the New World. The extinction coincides with the

settlement of the Americas The settlement of the Americas began when Paleolithic hunter-gatherers entered North America from the North Asian Mammoth steppe via the Beringia land bridge, which had formed between northeastern Siberia and western Alaska due to the lowering o ...

, and a kill site where a ''M. americanum'' was slaughtered and butchered is known, suggesting that hunting could have caused its extinction.

Description

''Megatherium americanum'' was one of the largest animals in its habitat, weighing up to , with a shoulder height of and length of from head to tail. It was one of the largest

ground sloths Ground sloths are a diverse group of extinct sloths in the mammalian superorder Xenarthra. The term is used to refer to all extinct sloths because of the large size of the earliest forms discovered, compared to existing tree sloths. The Carib ...

, about as big as modern

asian elephant The Asian elephant (''Elephas maximus''), also known as the Asiatic elephant, is the only living species of the genus ''Elephas'' and is distributed throughout the Indian subcontinent and Southeast Asia, from India in the west, Nepal in the no ...

s. ''Megatherium'' species were members of the abundant

Pleistocene megafauna Pleistocene megafauna is the set of large animals that lived on Earth during the Pleistocene epoch. Pleistocene megafauna became extinct during the Quaternary extinction event resulting in substantial changes to ecosystems globally. The role of ...

, 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 A tripod is a portable three-legged frame or stand, used as a platform for supporting the weight and maintaining the stability of some other object. The three-legged (triangular stance) design provides good stability against gravitational loads ...

, ''Megatherium'' could support its massive body weight while using the curved claws on its long

forelegs A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial (anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. ...

to pull down branches with the choicest leaves. This sloth, like a modern anteater, walked on the sides of its feet because its

claw A claw is a curved, pointed appendage found at the end of a toe or finger in most amniotes (mammals, reptiles, birds). Some invertebrates such as beetles and spiders have somewhat similar fine, hooked structures at the end of the leg or tarsus ...

s prevented it from putting them flat on the ground. Although it was primarily a

quadruped Quadrupedalism is a form of locomotion where four limbs are used to bear weight and move around. An animal or machine that usually maintains a four-legged posture and moves using all four limbs is said to be a quadruped (from Latin ''quattuor' ...

, its trackways show that it was capable of

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

locomotion. Biomechanical analysis also suggests it had adaptations to bipedalism. One study has proposed that ''Megatherium'' was mostly hairless, like modern elephants, because its large size and small

surface-area-to-volume ratio The surface-area-to-volume ratio, also called the surface-to-volume ratio and variously denoted sa/vol or SA:V, is the amount of surface area per unit volume of an object or collection of objects. SA:V is an important concept in science and engin ...

would have made it susceptible to overheating.

Mouth

''Megatherium'' had a narrow, cone-shaped mouth and

prehensile Prehensility is the quality of an appendage or organ that has adapted for grasping or holding. The word is derived from the Latin term ''prehendere'', meaning "to grasp". The ability to grasp is likely derived from a number of different orig ...

lips that were probably used to select particular plants and fruits. ''Megatherium'' also possessed the narrowest muzzle of all ground sloths from the Pleistocene, possibly meaning it was a very selective eater, able to carefully pick and choose which leaves and twigs to consume. While some evidence suggests the animal could use its tongue to differentiate and select its foliage, the lips probably had a more important role in this. In ''Megatherium'', the stylohyal and epihyal bones (parts of the hyoid bone which supports the tongue and is located in the throat) were fused together, and the apparatus lies farther upwards the throat, which, together with the elongated, steeply inclined mandibular symphysis, indicates a relatively shorter

geniohyoid muscle The geniohyoid muscle is a narrow muscle situated superior to the medial border of the mylohyoid muscle. It is named for its passage from the chin ("genio-" is a standard prefix for "chin") to the hyoid bone. Structure It arises from the inferi ...

and thus more limited capacity for tongue protrusion. Analysis of wear and the biomechanics of the chewing muscles suggests that they chewed vertically. Megatheres displayed deeper jaws than other sloths. Like other sloths, ''Megatherium'' lacked the enamel,

deciduous dentition Deciduous teeth or primary teeth, also informally known as baby teeth, milk teeth, or temporary teeth,Illustrated Dental Embryology, Histology, and Anatomy, Bath-Balogh and Fehrenbach, Elsevier, 2011, page 255 are the first set of teeth in the ...

and dental cusp patterns of other mammals. Instead of enamel, the tooth displays a layer of

cementum Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament.Illustrated Dental Embryology, Histology, ...

, ortho dentine and modified orthodentine, creating a soft, easily abraded surface. The teeth of ''M. americanum'' exhibit extreme

hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...

y, indicative of its gritty, fibrous diet. Their teeth in side view show interlocking V-shaped biting surfaces, although they are nearly square in cross-section and exhibit

bilophodont The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, ...

y. The teeth are spaced equidistantly in a series, located in the back of the mouth, which leaves space at the predentary, but with no

diastema A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...

, although the length of this tooth row and of the predentary spout can vary by species.

Taxonomy

''Megatherium'' is divided into 2 subgenera, ''Megatherium'' and ''Pseudomegatherium''. Taxonomy according to Pujos (2006): * Subgenus ''Megatherium'' **†''M. altiplanicum'' **†''M. americanum'' * Subgenus ''Pseudomegatherium'' ** †''M. celendinense'' ** †''M. medinae'' ** †''M. sundti'' ** †''M. urbinai'' Madrid MNCN-Megatherium americanum2

The first fossil specimen of ''Megatherium'' was discovered in 1788 by Manuel Torres, on the bank of the

Luján River The Luján River (Spanish, Río Luján) runs from its source near Espora about east of Buenos Aires, Argentina, to its outflow into the Río de la Plata north of the city. The first Megatherium fossil was found here in 1789. See also * List of ...

in

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. The fossil was shipped to

Museo Nacional de Ciencias Naturales The National Museum of Natural Sciences ( es, Museo Nacional de Ciencias Naturales) is the national museum of natural history of Spain. It is situated in the center of Madrid, by the Paseo de la Castellana. It is managed by the Spanish National Re ...

in

Madrid Madrid ( , ) is the capital and most populous city of Spain. The city has almost 3.4 million inhabitants and a Madrid metropolitan area, metropolitan area population of approximately 6.7 million. It is the Largest cities of the Europ ...

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, preceding the discovery of giant

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s some decades later. Since the original discovery, numerous other fossil ''Megatherium'' skeletons have been discovered across South America, in

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

,

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

,

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

,

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

, Colombia ( Quipile, Cundinamarca), Guyana,

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

,

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...

and

Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...

. 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. These species are considerably smaller than ''M. americanum'', and are considered to belong to a separate subgenus, ''Pseudomegatherium.'' The species ''Megatherium (Pseudomegatherium) tarijense,'' appears to be a junior synonym of ''M. americanum'', and merely a small individual. The species ''Megatherium filholi'' Moreno, 1888 of the Pampas, previously thought to be a junior synonym of ''M. americanum'' representing juvenile individuals, was suggested to be a distinct valid species in 2019. ''Megatherium gallardoi'' from the

Ensenadan The Ensenadan age is a period of geologic time (1.2–0.8 Ma) within the Early Pleistocene epoch of the Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the ...

of Argentina was suggested to be a valid species in 2008, most closely related to ''M. americanum'' and ''M. altiplanicum.'' ''M. parodii'' '','' and ''M. istilarti'' have not had their validity assessed in recent literature.

Evolution

Ground sloths are a diverse group belonging to superorder

Xenarthra Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. ...

, which also includes extinct pampatheres and glyptodonts, as well as living tree

sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their l ...

s, anteaters and armadillos. One of the four major

eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...

n radiations, this superorder evolved in isolation in South America while it was an island continent during the Paleogene and Neogene. The family to which ''Megatherium'' belongs,

Megatheriidae Megatheriidae is a family of extinct ground sloths that lived from approximately 23 mya—11,000 years ago. Megatheriids appeared during the Late Oligocene (Deseadan in the SALMA classification), some 29 million years ago, in South America ...

, is related within superfamily

Megatherioidea Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their li ...

to the extinct families

Nothrotheriidae Nothrotheriidae is a family of extinct ground sloths that lived from approximately 17.5 mya—10,000 years ago, existing for approximately . Previously placed within the tribe Nothrotheriini or subfamily Nothrotheriinae within Megatheriidae, th ...

and

Megalonychidae Megalonychidae is an extinct family of sloths including the extinct ''Megalonyx''. Megalonychids first appeared in the early Oligocene, about 35 million years (Ma) ago, in southern Argentina (Patagonia). There is actually one possible find datin ...

, and to living

three-toed sloth The three-toed or three-fingered sloths are arboreal neotropical mammals . They are the only members of the genus ''Bradypus'' and the family Bradypodidae. The four living species of three-toed sloths are the brown-throated sloth, the maned slot ...

s of family Bradypodidae, as deduced recently from collagen and mitochondrial DNA sequences obtained from subfossil bones. During the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Central American Isthmus Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. Ce ...

formed, causing the Great American Interchange, and a mass extinction of much of the indigenous South American megafauna. Xenarthrans were largely unaffected and continued to thrive in spite of competition from the northern immigrants. Ground sloths were prominent among the various South American animal groups to migrate northwards into North America, where they remained and flourished until the late

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

. The

rhinoceros A rhinoceros (; ; ), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species ...

-sized '' Promegatherium'' of the

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

is suggested to be the ancestor of ''Megatherium''. The oldest (and smallest) species of ''Megatherium'' is ''M. altiplanicum'' of Pliocene

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

. It was very similar to ''Promegatherium'', and was also about the size of a rhinoceros. ''M. tarijense'' has been regarded as a medium-sized ''Megatherium'' species, larger than ''M. altiplanicum'', but smaller than ''M. americanum''. It roamed from the Tarija Basin in

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

to Yantac in

Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = National seal , national_motto = "Firm and Happy f ...

. The oldest-known remains of ''Megatherium'' from the Pampas dates to the late Pliocene, around 3.58 million years ago. Species of ''Megatherium'' became larger over time, with the largest species, ''M. americanum'' of the Late Pleistocene, reaching the size of an African elephant. The oldest records of ''M. americanum'' are from the latter half of the

Middle Pleistocene The Chibanian, widely known by its previous designation of Middle Pleistocene, is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period. Th ...

, around 0.4 Ma (400 ka) ago.

Habitat

''Megatherium'' inhabited

woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (se ...

and

grassland A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...

environments of the lightly wooded areas of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

, with a Late Pleistocene range centred around the Pampas where it was an

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

species, as recently as 10,000 years ago. ''Megatherium'' was adapted to temperate, arid or semiarid open habitats. An example of these most recent finds is at

Cueva del Milodón Cuevas or Cueva (Spanish for "''cave(s)''") may refer to: Places * Cueva de Ágreda, a municipality located in the province of Soria, Castile and León, Spain * Cuevas Bajas, a town and municipality in the province of Málaga, part of the autono ...

in

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and g ...

n

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. The closely related genus ''

Eremotherium ''Eremotherium'' (from Greek for "steppe" or "desert beast": ἔρημος "steppe or desert" and θηρίον "beast") is an extinct genus of giant ground sloth, in the family Megatheriidae, the largest and most heavily built family of sloths. ' ...

'' (that has been classified occasionally as part of ''Megatherium'') lived in more tropical environments further north, and invaded temperate North America as part of the Great American Interchange.

Paleobiology

The giant ground sloth lived mostly in groups, but it may have lived singly in

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

s. It probably had mainly a browsing diet in open habitats, but also it probably fed on other moderate to soft tough food. For millions of years, the sloth did not have many enemies to bother it, so it was probably a diurnal animal. The giant ground sloth was a herbivore, feeding on leaves such as

yucca ''Yucca'' is a genus of perennial plant, perennial shrubs and trees in the family (biology), family Asparagaceae, subfamily Agavoideae. Its 40–50 species are notable for their Rosette (botany), rosettes of evergreen, tough, sword-shaped Leaf, ...

s,

agave ''Agave'' (; ; ) is a genus of monocots native to the hot and arid regions of the Americas and the Caribbean, although some ''Agave'' species are also native to tropical areas of North America, such as Mexico. The genus is primarily known for ...

s and

grasses Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns ...

. While it fed chiefly on terrestrial plants, it could also stand on its hind legs, using its tail as a balancing tripod, and reach for upper growth vegetation. It would pull itself upright to sit on its haunches or to stand and 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. It is likely that it spent a lot of time resting to aid digestion. Megatherium cuvieri - skull

A recent morpho-functional analysis indicates that ''M. americanum'' was adapted for strong vertical biting. The teeth are

hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...

and

bilophodont The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, ...

, and the sagittal section of each

loph The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, ...

is triangular with a sharp edge. This suggests that the teeth were used for cutting, rather than grinding, and that hard fibrous food was not the primary dietary component. While it has been suggested that the giant sloth may have been partly carnivorous, this is a controversial claim. Richard Fariña and Ernesto Blanco of the

Universidad de la República The University of the Republic ( es, Universidad de la República, sometimes ''UdelaR'') is Uruguay's oldest public university. It is by far the country's largest university, as well as the second largest public university in South America and t ...

in Montevideo have analysed a

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

skeleton of ''M. americanum'' and discovered that its

olecranon The olecranon (, ), is a large, thick, curved bony eminence of the ulna, a long bone in the forearm that projects behind the elbow. It forms the most pointed portion of the elbow and is opposite to the cubital fossa or elbow pit. The olecranon ...

—the part of the elbow to which the

triceps The triceps, or triceps brachii (Latin for "three-headed muscle of the arm"), is a large muscle on the back of the upper limb of many vertebrates. It consists of 3 parts: the medial, lateral, and long head. It is the muscle principally responsibl ...

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. They suggest that to add nutrients to its diet, ''Megatherium'' may have taken over the kills of ''

Smilodon ''Smilodon'' is a genus of the extinct machairodont subfamily of the felids. It is one of the most famous prehistoric mammals and the best known saber-toothed cat. Although commonly known as the saber-toothed tiger, it was not closely rela ...

''. Based on the estimated strength and

mechanical advantage Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The device trades off input forces against movement to obtain a desired amplification in the output force. The model for ...

of its biceps, it has been proposed that ''Megatherium'' could have overturned adult

glyptodon ''Glyptodon'' (from Greek for 'grooved or carved tooth': γλυπτός 'sculptured' and ὀδοντ-, ὀδούς 'tooth') is a genus of glyptodont (an extinct group of large, herbivorous armadillos) that lived from the Pleistocene, around 2.5 m ...

ts (large, armored xenarthrans, related to armadillos) as a means of scavenging or hunting these animals. However, noting that sloths lack the

carnassial Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified f ...

s typical of predators and that traces of bone are absent from the many preserved deposits of sloth dung,

Paul Martin Paul Edgar Philippe Martin (born August 28, 1938), also known as Paul Martin Jr., is a Canadian lawyer and politician who served as the 21st prime minister of Canada and the leader of the Liberal Party of Canada from 2003 to 2006. The son o ...

has described this proposal as "fanciful".

Carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numb ...

analysis has found that ''Megatherium'' has isotope values similar to other megafaunal herbivores such as

mammoths A mammoth is any species of the extinct elephantid genus ''Mammuthus'', one of the many genera that make up the order of trunked mammals called proboscideans. The various species of mammoth were commonly equipped with long, curved tusks and, i ...

,

glyptodon ''Glyptodon'' (from Greek for 'grooved or carved tooth': γλυπτός 'sculptured' and ὀδοντ-, ὀδούς 'tooth') is a genus of glyptodont (an extinct group of large, herbivorous armadillos) that lived from the Pleistocene, around 2.5 m ...

ts and ''

Macrauchenia ''Macrauchenia'' ("long llama", based on the now-invalid llama genus, ''Auchenia'', from Greek "big neck") was a large, long-necked and long-limbed, three-toed native South American mammal in the order Litopterna. The genus gives its name to its ...

'', and significantly unlike

omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...

and carnivorous mammals, suggesting that ''Megatherium'' was an obligate herbivore.

Extinction

In the south, the giant ground sloth flourished until about 10,500 radiocarbon years BP (8,500 BCE). Most cite the appearance of an expanding population of human hunters as the cause of its extinction. There are a few late dates of around 8,000 BP and one of 7,000 BP for ''Megatherium'' remains, but the most recent date viewed as credible is about 10,000 BP. The use of bioclimatic envelope modeling indicates that the area of suitable habitat for ''Megatherium'' had shrunk and become fragmented by the mid-Holocene. While this alone would not likely have caused its extinction, it has been cited as a possible contributing factor. Two ''M. americanum'' bones, an

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

and an

atlas vertebra In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. It is named for Atlas of Greek mythology because, just as Atlas supported the globe, it supports the entire head. The atlas i ...

, from separate collections, bear cut marks suggestive of butchery, with the latter suggested to represent an attempt to exploit the contents of the head. A kill site dating to around 12,600 BP is known from Campo Laborde in the Pampas in Argentina, where a single individual of ''M. americanum'' was slaughtered and butchered, which is the only confirmed giant ground-sloth kill site in the Americas. The study also questioned the Holocene dates previously obtained for Pampas megafauna, suggesting that they were due to humic acid contamination.

Cultural references

The ''

Megatherium Club The Megatherium Club was founded by William Stimpson. It 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. Many of the members had no f ...

'', named for the extinct animal and founded by

William Stimpson William Stimpson (February 14, 1832 – May 26, 1872) was a noted American scientist. He was interested particularly in marine biology. Stimpson became an important early contributor to the work of the Smithsonian Institution and later, dire ...

, was a group of

Washington, D.C. ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...

-based scientists who were attracted to that city by the

Smithsonian Institution The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...

's rapidly growing collection, from 1857 to 1866.

Notes

References

External links

BBC – ''Walking With Beasts'' – Megatherium

''London Review of Books'' – ''Bare Bones'' – Steven Shapin
* {{Taxonbar, from=Q310387 Prehistoric sloths Prehistoric placental genera Pliocene xenarthrans Pleistocene xenarthrans Piacenzian first appearances Holocene extinctions Pliocene mammals of South America Pleistocene mammals of South America Fossils of Argentina Fossils of Bolivia Fossils of Brazil Fossils of Chile Fossils of Colombia Fossils of Paraguay Fossils of Peru Fossils of Uruguay Fossil taxa described in 1796 Taxa named by Georges Cuvier