Megatherium

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Megatherium
Temporal range: Early
Ma
Possible later date of 0.008 Ma
M. americanum skeleton, Natural History Museum, London
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Pilosa
Clade:
Megatheria
Family: Megatheriidae
Subfamily: Megatheriinae
Genus: Megatherium
Cuvier, 1796
Type species
Megatherium americanum
Cuvier, 1796
Subgenera
Megatherium
  • M. altiplanicum Saint-Andre & De Iuliis, 2001
  • M. americanum Cuvier, 1796
Pseudomegatherium
  • M. celendinense Pujos, 2006
  • M. medinae Philippi, 1893
  • M. sundti Philippi, 1893
  • M. tarijense Gervais & Ameghino, 1880
  • M. urbiani Pujos & Salas, 2004
Map showing the distribution of all Megatherium species in red, inferred from fossil finds
Synonyms
  • Essonodontherium Ameghino 1884
  • Orocanthus Ameghino 1885
  • Neoracanthus Ameghino 1889

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 Pleistocene.[2] It is best known for the elephant-sized type species M. americanum, sometimes known as the giant ground sloth, or the megathere, native to the Pampas through southern Bolivia during the Pleistocene. Various other smaller species belonging to the subgenus Pseudomegatherium are known from the Andes.

Megatherium is part of the sloth family

kill sites where M. americanum was slaughtered and butchered is known, suggesting that hunting could have caused its extinction.[4]

Taxonomy

Megatherium is divided into 2 subgenera, Megatherium and Pseudomegatherium. Taxonomy according to Pujos (2006) and De Iuliis et al (2009):[5][6]

  • Subgenus Megatherium
    • M. altiplanicum Saint-André & de Iuliis 2001
    • M. americanum Cuvier 1796
  • Subgenus Pseudomegatherium Kraglievich 1931
    • M. celendinense Pujos 2006
    • M. medinae Philippi 1893
    • M. sundti Philippi 1893
    • M. tarijense Gervais & Ameghino, 1880
    • M. urbinai Pujos & Salas 2004
Specimen of M. americanum in Museo Nacional de Ciencias Naturales, Madrid, the first prehistoric animal skeleton mounted, in 1795.

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.[7]

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[8], 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.[3][8] 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.[3]

Fossils of Megatherium and other western megafauna proved popular with the Georgian-era public, preceding the discovery of giant dinosaurs some decades later.

Since the original discovery, numerous other fossil Megatherium skeletons have been discovered across South America, in

Celendin, Cajamarca Province in the Peruvian Andes.[5] These species are considerably smaller than M. americanum, and are considered to belong to a separate subgenus, Pseudomegatherium.[5]

The species Megatherium (Pseudomegatherium) tarijense, appears to be a junior synonym of M. americanum, and merely a small individual.[12]

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.[13]

Megatherium gallardoi Ameghino & Kraglievich 1921 from the Ensenadan of Argentina was suggested to be a valid species in 2008, most closely related to M. americanum and M. altiplanicum.[14]

M. parodii Hoffstetter 1949, and M. istilarti Kraglievich 1925 have not had their validity assessed in recent literature.

Evolution

Bru's 1796 skeletal drawing of M. americanum

subfossil bones.[citation needed
]

During the

Central American Isthmus 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.[17]

The

ka) ago.[19]

The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al., 2019).[15]

  
Folivora
  

Megalocnidae† (Caribbean sloths)

  Nothrotheriidae  

Nothrotheriops shastensis†    

  Megatheriidae  

Megatherium americanum

  Megalonychidae  

Megalonyx jeffersoni

Bradypodidae

  (three-fingered sloths)  

B. torquatus

B. pygmaeus

B. tridactylus

B. variegatus

Megatherioidea

Scelidotheriidae

Choloepodidae
(two-fingered sloths)

Mylodontidae

Mylodontoidea

Description

Reconstruction of Megatherium with hair (top) and without (bottom).

Megatherium americanum was one of the largest animals in its habitat, weighing up to 3.8–4.58 t (8,400–10,100 lb),

Pleistocene megafauna, large mammals that lived during the Pleistocene epoch.[citation needed
]

Megatherium had a robust

bipedal locomotion. Biomechanical analysis also suggests it had adaptations to bipedalism.[22]

One study has proposed that Megatherium was mostly hairless, like modern elephants, because its large size and small surface-area-to-volume ratio would have made it susceptible to overheating.[27]

Mouth

Megatherium had a narrow, cone-shaped mouth and

prehensile lips that were probably used to select particular plants and fruits.[28] 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.[28] 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.[29] 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 and thus more limited capacity for tongue protrusion.[30] Analysis of wear and the biomechanics of the chewing muscles suggests that they chewed vertically. Megatheres displayed deeper jaws than other sloths.[20]

Like other sloths, Megatherium lacked the

bilophodonty. 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, although the length of this tooth row and of the predentary spout can vary by species.[clarification needed][20]

Habitat

M. americanum restoration

Megatherium inhabited

endemic 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 in Patagonian Chile.[32] The closely related genus Eremotherium (that has been classified occasionally as part of Megatherium)[33] lived in more tropical environments further north, and invaded temperate North America as part of the Great American Interchange
.

Paleobiology

Restoration of M. americanum by Robert Bruce Horsfall, 1913

The giant ground sloth lived mostly in groups, but it may have lived singly in caves. 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.[citation needed]

The giant ground sloth was a herbivore, feeding on leaves such as

grasses.[citation needed] 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.[citation needed
] It is likely that it spent a lot of time resting to aid digestion.

M. americanum skull
Claw of Megatherium

A recent morpho-functional analysis

bilophodont, and the sagittal section of each loph
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

omnivorous and carnivorous mammals, suggesting that Megatherium was an obligate herbivore.[35]

Extinction

M. americanum sculpture in Crystal Palace Park

The youngest unambiguous dates for Megatherium are from the end of the Late Pleistocene. Supposed early Holocene dates obtained for Megatherium and other Pampas megafauna have been questioned, with suggestions that they are likely due to

Quaternary extinction event.[36] 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.[37]

Towards the end of the Late Pleistocene, humans first arrived in the Americas, with some of the earliest evidence of humans in South America being the

kill site dating to around 12,600 years Before Present (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. At the site several stone tools were present, including the fragment of a projectile point.[4] Another possible kill site is Arroyo Seco 2 near Tres Arroyos in the Pampas in Argentina, where M. americanum bones amongst those of other megafauna were found associated with humans artifacts dating to approximately 14,782–11,142 cal yr BP.[42] This hunting may have been a factor in its extinction.[39]

Cultural references

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.

Notes

References

  1. ^ a b c Saint-André, P. A.; De Iuliis, G. (2001). "The smallest and most ancient representative of the genus Megatherium Cuvier, 1796 (Xenarthra, Tardigrada, Megatheriidae), from the Pliocene of the Bolivian Altiplano" (PDF). Geodiversitas. 23 (4): 625–645. Archived from the original (PDF) on 2013-10-29. Retrieved 14 April 2016.
  2. ^ .
  3. ^ .
  4. ^ .
  5. ^ .
  6. .
  7. .
  8. ^ .
  9. ^ Bürgl, Hans (1956). "Restos de Megatherium y otros fósiles de Quipile, Cundinamarca". Ingeominas: 1–14. Retrieved 2017-05-03.
  10. ^ De Porta, Jaime (1961). "La posición estratigráfica de la fauna de Mamíferos del pleistoceno de la Sabana de Bogotá". Boletín de Geología, Universidad Industrial de Santander. 7: 37–54. Retrieved 2017-05-03.
  11. .
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  15. ^ (PDF) from the original on 2022-10-09.
  16. .
  17. . Retrieved 2014-09-11.
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  19. .
  20. ^ a b c d Bargo, M. S. (2001). "The ground sloth Megatherium americanum: Skull shape, bite forces, and diet" (PDF). Acta Palaeontologica Polonica. 46 (2): 173–192. Archived (PDF) from the original on 2022-10-09. Retrieved 2012-07-22.
  21. ^ Blanco, R.E; Czerwonogora, Ada (2003). "The gait of Megatherium Cuvier 1796 (Mammalia, Xenarthra, Megatheriidae)". Senckenbergiana Biologica. 83 (1): 61–68.
  22. ^ .
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  25. ^ BBC (2012). "Megatherium Wildfacts". BBC. Archived from the original on 2014-02-01. Retrieved 2012-07-22.
  26. .
  27. ^ Fariña, R. (June 2002). "Megatherium, the hairless: appearance of the great Quaternary sloths (Mammalia;Xenarthra)". Ameghiniana. 39 (2): 241–244 – via ResearchGate.
  28. ^
    S2CID 39664746
    .
  29. ^ .
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  32. ^ C. Michael Hogan (2008) Cueva del Milodon, Megalithic Portal
  33. . Retrieved 2014-05-27.
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    OCLC 1084743779.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
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External links