Megatheriidae

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Megatheriidae
Temporal range: Late Oligocene (Deseadan)-Early Holocene (Lujanian)
~29–0.008 Ma
Eremotherium skeleton, NMNH, Washington, DC.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Pilosa
Clade: Megatheria
Family: Megatheriidae
J. E. Gray 1821
Type genus
Megatherium americanum
Subgroups
Closeup of hand, showing claws
Closeup of skull

Megatheriidae is a family of extinct ground sloths that lived from approximately 23 mya—11,000 years ago.[3]

Megatheriids appeared during the Late Oligocene (Deseadan in the SALMA classification), some 29 million years ago, in South America. The group includes the heavily built Megatherium (given its name 'great beast' by Georges Cuvier[4]) and Eremotherium. An early genus that was originally considered a megatheriid, the more slightly built Hapalops, reached a length of about 1.2 metres (3.9 ft). The nothrotheres have recently been placed in their own family, Nothrotheriidae.[5]

The skeletal structure of these ground sloths indicates that the animals were massive. Their thick bones and even thicker joints (especially those on the hind legs) gave their appendages tremendous power that, combined with their size and fearsome claws, provided a formidable defense against predators.

The earliest megatheriid in North America was Sibotherium which arrived 5.3 million years ago, after crossing the recently formed Panamanian land bridge. At more than five tons in weight, 6 metres (20 ft) in length, and able to reach as high as 5.2 metres (17 ft), Eremotherium was taller than an African bush elephant bull. Unlike relatives, this species retained a plesiomorphic extra claw. While other species of Eremotherium had four fingers with only two or three claws, E. eomigrans had five fingers, four of them with claws up to nearly 30 centimetres (1 ft) long.[6]

Phylogeny[edit]

The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al., 2019).[7]

Folivora

Megalocnidae (Caribbean sloths)

Mylodontoidea

Scelidotheriidae

Mylodontidae

   Choloepodidae (two-toed sloths)

Megatherioidea

Megalonyx jeffersoni

Bradypodidae

Bradypus torquatus

Bradypus pygmaeus

Bradypus tridactylus

Bradypus variegatus

(three-toed sloths)

Nothrotheriops shastensis

Megatherium americanum


The following phylogeny is based on Varela et al. 2019.[8]

Folivora

Pseudoglyptodon

Bradypodidae 

Bradypus

Eufolivora 
Mylodontidae 

Nematherium

Scelidotheriinae 

Analcitherium

Neonematherium

Sibyllotherium

Proscelidodon

Catonyx

Scelidotherium

Valgipes

Pseudoprepotherium

Orophodontinae

Brievabradys

Octodontotherium

Paroctodontotherium

Octomylodon

Urumacotherium

Baraguatherium

Octodontobradys

Mylodontinae 

Mylodon

Thinobadistes

Lestodon

Lestobradys

Bolivartherium

Simomylodon

Pleurolestodon

Glossotherium

Paramylodon

Megatherioidea 

Schismotherium

Pelecyodon

Megalonychidae 

Hapalops

Hyperleptus

Eucholoeops

Pseudortotherium

Megalonychotherium

Megalonychinae 

Pliometanastes

Megalonyx

Australonyx

Megistonyx

Ahytherium

Pliomorphus

Megalocninae 

Megalocnus

Parocnus

Choloepodinae 

Acratocnus

Neocnus

Choloepus

Megatheria 

Analcimorphus

Nothrotheriidae 
Thalassocninae 

Thalassocnus

Nothrotheriinae 

Lakukullus

Mionothropus

Nothrotherium

Nothrotheriops

Pronothrotherium

Aymaratherium

Xyophorus

Megatheriidae 
Planopsinae 

Prepoplanops

Planops

Prepotherium

Megatheriinae 

Diabolotherium

Megathericulus

Anisodontherium

Pyramiodontherium

Proeremotherium

Eremotherium

Megatherium

References[edit]

  1. ^ Eli Amson; Christian de Muizon; Timothy J. Gaudin (2017). "A reappraisal of the phylogeny of the Megatheria (Mammalia: Tardigrada), with an emphasis on the relationships of the Thalassocninae, the marine sloths" (PDF). Zoological Journal of the Linnean Society. 179 (1): 217–236. doi:10.1111/zoj.12450.
  2. ^ Varela, L.; Tambusso, P.S.; McDonald, H.G.; Fariña, R.A.; Fieldman, M. (2019). "Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis". Systematic Biology. 68 (2): 204–218. doi:10.1093/sysbio/syy058. PMID 30239971.
  3. ^ Paleobiology Database: Megatheriidae
  4. ^ G. Cuvier (1796)
  5. ^ Muizon, C. de; McDonald, H. G.; Salas, R.; Urbina, M. (June 2004). "The Youngest Species of the Aquatic Sloth Thalassocnus and a Reassessment of the Relationships of the Nothrothere Sloths (Mammalia: Xenarthra)". Journal of Vertebrate Paleontology. 24 (2). Society of Vertebrate Paleontology: 387–397. Bibcode:2004JVPal..24..387D. doi:10.1671/2429a. S2CID 83732878. Retrieved 2009-01-29.
  6. ^ De Iuliis and Cartelle (1999)
  7. ^ Presslee, S.; Slater, G. J.; Pujos, F.; Forasiepi, A. M.; Fischer, R.; Molloy, K.; et al. (2019). "Palaeoproteomics resolves sloth relationships" (PDF). Nature Ecology & Evolution. 3 (7): 1121–1130. Bibcode:2019NatEE...3.1121P. doi:10.1038/s41559-019-0909-z. PMID 31171860. S2CID 174813630. Archived (PDF) from the original on 12 September 2020. Retrieved 18 September 2020.
  8. ^ Varela, L.; Tambusso, P. S.; McDonald, H. G.; Fariña, R. A. (2018). "Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis". Systematic Biology. 68 (2): 204–218. doi:10.1093/sysbio/syy058. PMID 30239971.

External links[edit]