Nothrotheriidae is a family of
extinctground sloths that lived from approximately 17.5
mya—10,000 years ago, existing for approximately 17.49 million years.[7] Previously placed within the tribe Nothrotheriini or subfamily Nothrotheriinae within
Megatheriidae, they are now usually placed in their own family, Nothrotheriidae.[8] 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.[8][9][10] However, the family placement of Thalassocnus has been disputed; while long considered a nothrotheriid, one recent analysis moves it to
Megatheriidae,[1] while another retains it in a
basal position within Nothrotheriidae.[2]
The only known nothrotheriid in North America was Nothrotheriops, which appeared at the beginning of the
Pleistocene, about 2.6 Ma ago.[11]Nothrotherium reached Mexico (
Nuevo Leon) by the late Pleistocene.[12]
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).[13]
^François Pujos, Gerardo De Iuliis, Bernardino Mamani Quispe & Ruben Andrade Flores (2014) Lakukullus anatisrostratus, gen. et sp. nov., a new massive nothrotheriid sloth (Xenarthra, Pilosa) from the middle Miocene of Bolivia,Journal of Vertebrate Paleontology, 34:5,1243-1248, DOI: 10.1080/02724634.2014.849716
^
abMuizon, 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.
S2CID83732878.
^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.
PMID30239971.