Nothrotheriidae

Nothrotheriidae Temporal range: Early Miocene Early Holocene (Irvingtonian-Rancholabrean (NALMA) & Colhuehuapian-Lujanian) (SALMA) ~
Shasta ground sloth (Nothrotheriops shastense), Peabody Museum
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Pilosa
Clade:	†Megatheria
Family:	†Nothrotheriidae (Ameghino 1920) C. de Muizon et al. 2004
Genera
†Neohapalops †Thalassocnus? †Nothrotheriinae (Ameghino, 1920) C. de Muizon et al. 2004 †Amphibradys †Aymaratherium †Chasicobradys †Huilabradys †Lakukullus †Mcdonaldocnus †Mionothropus †Nothropus †Nothrotheriops †Nothrotherium †Pronothrotherium †Xyophorus

Nothrotheriidae is a family of extinct ground sloths that lived from approximately 19.8 mya—10,000 years ago, existing for approximately 19.79 million years. Previously placed within the tribe Nothrotheriini or subfamily Nothrotheriinae within Megatheriidae, they are now usually placed in their own family, Nothrotheriidae. Nothrotheriids appeared in the Burdigalian, some 19.8 million years ago, in South America. The group includes the comparatively slightly built Nothrotheriops, which reached a length of about 2.75 metres (9.0 ft). While nothrotheriids were small compared to some of their megatheriid relatives, their claws provided an effective defense against predators, like those of larger anteaters today.

Evolution

During the late Miocene and Pliocene, the sloth genus Thalassocnus of the west coast of South America became adapted to a shallow-water marine lifestyle. However, the family placement of Thalassocnus has been disputed; while long considered a nothrotheriid, one recent analysis moves it to Megatheriidae, while another retains it in a basal position within Nothrotheriidae.

The only known nothrotheriid in North America was Nothrotheriops, which appeared at the beginning of the Pleistocene, about 2.6 Ma ago. Nothrotherium reached Mexico (Nuevo Leon) by the late Pleistocene.

Subfossilized Nothrotheriops shastensis dung in Rampart Cave, Arizona (NPS, 1938)

The last ground sloths in North America belonging to Nothrotheriidae, the Shasta ground sloth (Nothrotheriops shastensis), died so recently that their dried subfossilized dung has remained undisturbed in some caves – such as the Rampart Cave, located on the Arizona side of the Lake Mead National Recreation Area – as if it were just recently deposited. A Shasta ground sloth skeleton, found in a lava tube at Aden Crater in New Mexico, still had skin and hair preserved, and is now at the Yale Peabody Museum. The largest samples of Nothrotheriops dung can be found in the collections of the National Museum of Natural History.

Phylogeny

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

Folivora

Megalocnidae (Caribbean sloths)             Nothrotheriidae   Nothrotheriops shastensis         Megatheriidae   Megatherium americanum       Megalonychidae Megalonyx jeffersoni   Bradypodidae   (three-toed sloths)     B. torquatus       B. pygmaeus       B. tridactylus     B. variegatus           Megatherioidea       Scelidotheriidae       Choloepodidae (two-toed sloths)     Mylodontidae     Mylodontoidea

Here is a more detailed phylogeny of the Nothrotheriidae based on Varela et al. 2018.

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