Megatheriidae

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

Megatheriidae Temporal range: Late Oligocene (Deseadan)-Early Holocene (Lujanian) ~29–0.008 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Eremotherium skeleton, NMNH, Washington, DC.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Pilosa
Superfamily:	Megatherioidea
Clade:	†Megatheria
Family:	†Megatheriidae J. E. Gray 1821
Type genus
†Megatherium americanum
Subgroups
†Thalassocnus?[1][2] †Planopsinae †Planops †Prepoplanops †Prepotherium †Proprepotherium †Megatheriinae

Closeup of hand, showing claws

Closeup of skull

Megatheriids appeared during the Late Oligocene (Deseadan in the SALMA classification), some 29 million years ago, in South America. The group includes the largest known ground sloths, the elephant sized 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 when fully erect 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

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 † Megalonychidae † Megalonyx jeffersoni Bradypodidae Bradypus torquatus Bradypus pygmaeus Bradypus tridactylus Bradypus variegatus (three-toed sloths) † Nothrotheriidae † Nothrotheriops shastensis † Megatheriidae   † 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