Editing Ground sloth

{{Short description|Diverse group of extinct sloth species}}
{{Paraphyletic group
| auto = yes
| name = Ground sloths
| fossil_range = {{Fossil range|35|0.005}}<small>Late [[Eocene]] –  [[Holocene]]</small>
| image = Ground sloths.jpg
| image_caption = [[American Museum of Natural History]] mounts of (from left) ''[[Megalocnus]] rodens'', ''[[Scelidotherium]] cuvieri'', ''[[Megalonyx]] wheatleyi'', ''[[Glossotherium]] robustus''
| parent = Folivora
| includes_text = Families
| includes = 
* †[[Megalocnidae]] (in part)
* †[[Megalonychidae]]
* †[[Megatheriidae]]
* †[[Nothrotheriidae]]
* †[[Mylodontidae]]
* †[[Scelidotheriidae]]
}}

'''Ground sloths''' are a diverse group of [[extinct]] [[sloth]]s in the [[mammal]]ian [[superorder]] [[Xenarthra]]. They varied widely in size with the largest, belonging to genera ''[[Lestodon]]'', ''[[Eremotherium]]'' and ''[[Megatherium]]'', being around the size of [[elephants]]. Ground sloths represent a [[paraphyletic group]], as living tree sloths are thought to have evolved from ground sloth ancestors.

The early evolution of ground sloths took place during the late [[Paleogene]] and [[Neogene]] of South America, while the continent was isolated. At their earliest appearance in the fossil record, they were already distinct at the family level. Sloths dispersed into the [[Greater Antilles]] during the [[Oligocene]], and the presence of intervening islands between the American continents in the [[Miocene]] allowed a dispersal of some species into North America. They were hardy as evidenced by their high species diversity and their presence in a wide variety of environments, extending from the far south of [[Patagonia]] ([[Cueva del Milodón Natural Monument]]) to [[Alaska]].<ref>C.M. Hogan (2008)</ref><ref>{{Cite journal |last=Stock |first=Chester |date=1942-05-29 |title=A Ground Sloth in Alaska |url=http://dx.doi.org/10.1126/science.95.2474.552 |journal=Science |volume=95 |issue=2474 |pages=552–553 |bibcode=1942Sci....95..552S |doi=10.1126/science.95.2474.552 |issn=0036-8075 |pmid=17790868|url-access=subscription }}</ref><ref>{{Cite journal |last1=McDonald |first1=H.G. |last2=Harington |first2=C.R. |last3=De Iuliis |first3=G. |date=2000-01-01 |title=The Ground Sloth, Megalonyx, from Pleistocene Deposits of the Old Crow Basin, Yukon, Canada |journal=Arctic |volume=53 |issue=3 |doi=10.14430/arctic852 |issn=1923-1245 |doi-access=free}}</ref> Sloths, and xenarthrans as a whole, represent one of the more successful South American groups during the [[Great American Interchange]] after the connection of North and South America during the late [[Pliocene]] with a number of ground sloth genera migrating northwards. One genus, ''[[Thalassocnus]],'' even adapted for marine life along the Pacific coast of South America during the late Miocene and Pliocene epochs.

Ground sloths, which were represented by over 30 living species during the [[Late Pleistocene]], abruptly became extinct on the American mainland as part of the [[Late Pleistocene extinctions|end-Pleistocene extinction event]] around 12,000 years ago, simultaneously with the majority of other large animals in the Americas. Their extinction has been posited to be the result of hunting by recently arrived humans and/or climate change.<ref name="Fiedal">{{cite book |last=Fiedal |first=Stuart |series=Vertebrate Paleobiology and Paleoanthropology |title=American Megafaunal Extinctions at the End of the Pleistocene |publisher=[[Springer Science+Business Media|Springer]] |year=2009 |isbn=978-1-4020-8792-9 |editor-last=Haynes |editor-first=Gary |pages=21–37 |contribution=Sudden deaths: The chronology of terminal Pleistocene megafaunal extinction |doi=10.1007/978-1-4020-8793-6_2}}</ref><ref>{{Cite web |last=Mason |first=Betsy |date=August 1, 2005 |title=Humans Drove Giant Sloths to Extinction |url=https://www.science.org/content/article/humans-drove-giant-sloths-extinction |access-date=2022-10-02 |website=www.science.org |language=en}}</ref> A number of [[kill site]]s are known where humans butchered ground sloths dating just prior to their extinction.

The [[Megalocnidae|Caribbean ground sloths]], the most recent survivors, lived on [[Cuba]] and [[Hispaniola]], possibly until 1550&nbsp;BCE. However, [[radiocarbon dating]] suggests an age of between 2819 and 2660&nbsp;BCE for the last occurrence of ''[[Megalocnus]]'' in [[Cuba]].<ref name="MacPhee">{{cite journal |last1=MacPhee |first1=R.D.E. |author2=Iturralde-Vinent, M.A. |author3=Vázquez, O.J. |date=June 2007 |title=Prehistoric Sloth Extinctions in Cuba: Implications of a New 'Last' Appearance Date |url=https://bioone.org/journals/caribbean-journal-of-science/volume-43/issue-1/cjos.v43i1.a9/Prehistoric-Sloth-Extinctions-in-Cuba--Implications-of-a-New/10.18475/cjos.v43i1.a9.short |journal=[[Caribbean Journal of Science]] |publisher=College of Arts and Sciences, [[University of Puerto Rico at Mayagüez|University of Puerto Rico]] |volume=43 |issue=1 |pages=94–98 |doi=10.18475/cjos.v43i1.a9 |access-date=11 May 2009 |s2cid=56003217|url-access=subscription }}</ref> They survived 5,000–6,000&nbsp;years longer in the [[Caribbean]] than on the American mainland, which correlates with the later colonization of this area by humans.<ref name="Steadman_2005">{{cite journal |last1=Steadman |first1=D.W. |author2=Martin, P.S. |author3=MacPhee, R.D.E. |author4=Jull, A.J.T. |author5=McDonald, H.G. |author6=Woods, C.A. |author7=Iturralde-Vinent, M. |author8=Hodgins, G.W.L. |author1-link = David Steadman |author2-link=Paul Schultz Martin |title=Asynchronous extinction of late Quaternary sloths on continents and islands |journal=[[Proceedings of the National Academy of Sciences]] |volume=102 |issue=33 |pages=11763–11768 |publisher=[[United States National Academy of Sciences]] |date=2005-08-16 |doi=10.1073/pnas.0502777102 |pmid=16085711 |pmc=1187974 |bibcode=2005PNAS..10211763S |doi-access=free }}</ref>

== Description ==
[[File:Ground sloth size comparison.png|thumb|Size comparison of various ground sloths compared to a human, including ''[[Megatherium|Megatherium americanum]]'' (A, top left) ''[[Eremotherium laurillardi]]'' (B, top right), ''[[Lestodon armatus]]'' (C, middle left) ''[[Mylodon darwinii]]'' (D, middle right) ''[[Glossotherium robustum]]'' (E, bottom left) and ''[[Catonyx|Catonyx cf. C. cuvieri]]'' (F, bottom right)]]
Ground sloths varied widely in size from under {{Convert|100|kg|lb}} in the Caribbean ground sloths, to {{Convert|3700-4100|kg|lb}} in the largest ground sloth genera ''[[Megatherium]]'', ''[[Lestodon]]'' and ''[[Eremotherium]].''<ref name=":4" /><ref>{{Cite journal |last1=Bargo |first1=M. Susana |last2=Vizcaíno |first2=Sergio F. |last3=Archuby |first3=Fernando M. |last4=Blanco |first4=R. Ernesto |date=2000-09-25 |title=Limb bone proportions, strength and digging in some Lujanian (Late Pleistocene-Early Holocene) mylodontid ground sloths (Mammalia, Xenarthra) |url=http://www.tandfonline.com/doi/abs/10.1671/0272-4634%282000%29020%5B0601%3ALBPSAD%5D2.0.CO%3B2 |journal=Journal of Vertebrate Paleontology |language=en |volume=20 |issue=3 |pages=601–610 |doi=10.1671/0272-4634(2000)020[0601:LBPSAD]2.0.CO;2 |issn=0272-4634|url-access=subscription }}</ref> The bodies of ground sloths were generally barrel-shaped, with a broad pelvis.<ref name=":9">{{Cite journal |last=Naish |first=Darren |date=November 2005 |title=Fossils explained 51: Sloths |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2451.2005.00538.x |journal=Geology Today |language=en |volume=21 |issue=6 |pages=232–238 |doi=10.1111/j.1365-2451.2005.00538.x |issn=0266-6979|url-access=subscription }}</ref> The skull shapes of ground sloths are highly variable.<ref name=":10" /> Like other xenarthrans, the adult teeth of ground sloths lacked [[Tooth enamel|enamel]], with the tooth surface being composed of relatively soft [[Dentin|orthodentine]].<ref>Resar, N. A., Green, J. L., & McAfee, R. K. (2013). Reconstructing paleodiet in ground sloths (Mammalia, Xenarthra) using dental microwear analysis. ''Kirtlandia,'' ''58,'' 61–72.</ref> The number of teeth in the jaws is considerably reduced in comparison to other mammals, with most ground sloths only having 5 and 4 teeth in each half of the upper and lower jaws respectively, with some ground sloths exhibiting further tooth number reduction.<ref name=":7">{{Cite journal |last1=Hautier |first1=Lionel |last2=Gomes Rodrigues |first2=Helder |last3=Billet |first3=Guillaume |last4=Asher |first4=Robert J. |date=2016-06-14 |title=The hidden teeth of sloths: evolutionary vestiges and the development of a simplified dentition |journal=Scientific Reports |language=en |volume=6 |issue=1 |page=27763 |doi=10.1038/srep27763 |issn=2045-2322 |pmc=4906291 |pmid=27297516|bibcode=2016NatSR...627763H }}</ref> These teeth were rootless<ref name=":7" /> and were continuously growing (hypselodont), and typically have a relatively simple morphology.<ref name=":10" /> There are generally no teeth at the front of the jaws. In order to be able to grasp food, those whose skulls exhibit narrow muzzles are likely to have had prehensile, [[black rhinoceros]]-like upper lips, while those with wider muzzles are likely to have had a square, [[white rhinoceros]] like upper-lip, used in combination with mobile tongues.<ref name=":10">{{Cite journal |last1=Bargo |first1=M. Susana |last2=Toledo |first2=Néstor |last3=Vizcaíno |first3=Sergio F. |date=February 2006 |title=Muzzle of South American Pleistocene ground sloths (Xenarthra, Tardigrada) |url=https://onlinelibrary.wiley.com/doi/10.1002/jmor.10399 |journal=Journal of Morphology |language=en |volume=267 |issue=2 |pages=248–263 |doi=10.1002/jmor.10399 |pmid=16315216 |issn=0362-2525|url-access=subscription }}</ref> Some ground sloths have canine-like teeth at the front of the jaws separated from the other teeth by a gap (diastema).<ref name=":9" /> The hands of ground sloths have [[ungual]] phalanges that indicate that they had well developed claws.<ref>{{Cite journal |last1=Patiño |first1=Santiago J. |last2=Fariña |first2=Richard A. |date=2017-11-17 |title=Ungual phalanges analysis in Pleistocene ground sloths (Xenarthra, Folivora) |url=https://www.tandfonline.com/doi/full/10.1080/08912963.2017.1286653 |journal=Historical Biology |language=en |volume=29 |issue=8 |pages=1065–1075 |doi=10.1080/08912963.2017.1286653 |bibcode=2017HBio...29.1065P |issn=0891-2963|url-access=subscription }}</ref> In many ground sloth families (Megatheriidae, Mylodontidae, Scelidotheriidae and Nothrotheriidae), the hindfoot is inwardly rotated, meaning sole faces inwards and that the body weight was primarily borne on the fifth [[Metatarsal bones|metatarsus]] and the [[calcaneum]].<ref>H.G. McDonald [https://books.google.com/books?id=bGbmCQAAQBAJ&dq=ground+sloth+walking&pg=PA201 Biomechanical inferences of locomotion in ground sloths: integrating morphological and track data]. New Mexico Mus Nat. Hist. Sci. Bull., 42 (2007), pp. 201-208</ref>

== Ecology ==
Ground sloths are generally regarded as herbivores, with some being [[Browsing (herbivory)|browsers]],<ref>{{Cite journal |last1=Saarinen |first1=Juha |last2=Karme |first2=Aleksis |date=June 2017 |title=Tooth wear and diets of extant and fossil xenarthrans (Mammalia, Xenarthra) – Applying a new mesowear approach |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018216306630 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |language=en |volume=476 |pages=42–54 |bibcode=2017PPP...476...42S |doi=10.1016/j.palaeo.2017.03.027|url-access=subscription }}</ref> others [[Grazing (behaviour)|grazers]],<ref>{{Cite journal |last1=van Geel |first1=Bas |last2=van Leeuwen |first2=Jacqueline F.N. |last3=Nooren |first3=Kees |last4=Mol |first4=Dick |last5=den Ouden |first5=Natasja |last6=van der Knaap |first6=Pim W.O. |last7=Seersholm |first7=Frederik V. |last8=Rey-Iglesia |first8=Alba |last9=Lorenzen |first9=Eline D. |date=January 2022 |title=Diet and environment of Mylodon darwinii based on pollen of a Late-Glacial coprolite from the Mylodon Cave in southern Chile |journal=Review of Palaeobotany and Palynology |language=en |volume=296 |pages=104549 |bibcode=2022RPaPa.29604549V |doi=10.1016/j.revpalbo.2021.104549 |s2cid=239902623 |doi-access=free}}</ref> and some intermediate between the two as mixed feeders (both browsing and grazing),<ref>{{Cite journal |last1=Pujos |first1=François |last2=Gaudin |first2=Timothy J. |last3=De Iuliis |first3=Gerardo |last4=Cartelle |first4=Cástor |date=September 2012 |title=Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths |url=http://link.springer.com/10.1007/s10914-012-9189-y |journal=Journal of Mammalian Evolution |language=en |volume=19 |issue=3 |pages=159–169 |doi=10.1007/s10914-012-9189-y |issn=1064-7554 |s2cid=254701351 |hdl-access=free |hdl=11336/69736}}</ref> though a number of authors have argued that some ground sloths may have been omnivores.<ref name=":6">{{Cite journal |last1=Tejada |first1=Julia V. |last2=Flynn |first2=John J. |last3=MacPhee |first3=Ross |last4=O’Connell |first4=Tamsin C. |last5=Cerling |first5=Thure E. |last6=Bermudez |first6=Lizette |last7=Capuñay |first7=Carmen |last8=Wallsgrove |first8=Natalie |last9=Popp |first9=Brian N. |date=2021-10-07 |title=Isotope data from amino acids indicate Darwin's ground sloth was not an herbivore |journal=Scientific Reports |language=en |volume=11 |issue=1 |page=18944 |doi=10.1038/s41598-021-97996-9 |issn=2045-2322 |pmc=8494799 |pmid=34615902|bibcode=2021NatSR..1118944T }}</ref> Sloths that had longer snouts are presumed to have had greater olfactory acuity, but appear to have also had less binocular vision and poorer ability to localize sounds. A number of extinct sloth species are thought to have had hearing abilities optimized for low frequencies, perhaps related to use of [[infrasound]] for communication.<ref name="Blanco2012">{{cite journal |last1=Blanco |first1=R.E. |last2=Rinderknecht |first2=A. |year=2012 |title=Fossil evidence of frequency range of hearing independent of body size in South American Pleistocene ground sloths (Mammalia, Xenarthra) |journal=Comptes Rendus Palevol |volume=11 |issue=8 |pages=549–554 |bibcode=2012CRPal..11..549B |doi=10.1016/j.crpv.2012.07.003}}</ref><ref name="Blanco2014">{{cite journal |last1=Blanco |first1=R.E. |last2=Jones |first2=W.W. |year=2014 |title=Estimation of hearing capabilities of Early Miocene sloths (Mammalia, Xenarthra, Folivora) and palaeobiological implications |journal=Historical Biology |volume=28 |issue=3 |pages=390–397 |doi=10.1080/08912963.2014.946415 |s2cid=84691573}}</ref> Some ground sloths are suggested to have dug [[burrow]]s.<ref>Yizcaino,S.F.,Zdrate, M., Bargo, M.S., & Dondas, A. 2001. Pleistocene burrows in the Mar del Plata area (Argentina) and their probable builders. - Acta Palaeontologica Polonica 46, 2, 289-301</ref><ref>{{Cite journal |last1=Lopes |first1=Renato Pereira |last2=Frank |first2=Heinrich Theodor |last3=Buchmann |first3=Francisco Sekiguchi de Carvalho |last4=Caron |first4=Felipe |date=2017-04-03 |title=Megaichnus igen. nov.: Giant Paleoburrows Attributed to Extinct Cenozoic Mammals from South America |url=https://www.tandfonline.com/doi/full/10.1080/10420940.2016.1223654 |journal=Ichnos |language=en |volume=24 |issue=2 |pages=133–145 |bibcode=2017Ichno..24..133L |doi=10.1080/10420940.2016.1223654 |issn=1042-0940 |s2cid=133305289 |hdl-access=free |hdl=11449/162902}}</ref> Their skeletal anatomy suggests that they were incapable of running, and relied on other strategies to defend against predators,<ref name=":8">{{Cite journal |last=McDonald |first=H. Gregory |date=September 2012 |title=Evolution of the Pedolateral Foot in Ground Sloths: Patterns of Change in the Astragalus |url=http://link.springer.com/10.1007/s10914-011-9182-x |journal=Journal of Mammalian Evolution |language=en |volume=19 |issue=3 |pages=209–215 |doi=10.1007/s10914-011-9182-x |issn=1064-7554|url-access=subscription }}</ref> though they were likely significantly more active and agile than living tree sloths.<ref>{{Cite journal |last1=Billet |first1=G. |last2=Germain |first2=D. |last3=Ruf |first3=I. |last4=de Muizon |first4=C. |last5=Hautier |first5=L. |date=December 2013 |title=The inner ear of Megatherium and the evolution of the vestibular system in sloths |journal=Journal of Anatomy |language=en |volume=223 |issue=6 |pages=557–567 |doi=10.1111/joa.12114 |issn=0021-8782 |pmc=3842198 |pmid=24111879}}</ref> Ground sloths were likely able to adopt a bipedal stance while stationary, allowing the forelimbs to be used to grasp vegetation as well as to use their claws for defence, though whether they were capable of moving in this posture is uncertain.<ref>{{Cite journal |last1=Toledo |first1=Nestor |last2=Arregui |first2=Mariano |date=2023-02-01 |title=Concurrent evidence from ichnology and anatomy: the scelidotheriine ground sloths (Xenarthra, Folivora) from the Pleistocene of Argentina |url=https://www.tandfonline.com/doi/full/10.1080/08912963.2022.2035379 |journal=Historical Biology |language=en |volume=35 |issue=2 |pages=284–292 |bibcode=2023HBio...35..284T |doi=10.1080/08912963.2022.2035379 |issn=0891-2963 |s2cid=246698665|url-access=subscription }}</ref><ref name=":8" /> Some ground sloths have been suggested to be able to climb.<ref>{{Cite journal |last1=Stinnesbeck |first1=Sarah R. |last2=Frey |first2=Eberhard |last3=Avilés Olguín |first3=Jerónimo |last4=González |first4=Arturo González |last5=Velázquez Morlet |first5=Adriana |last6=Stinnesbeck |first6=Wolfgang |date=2021-11-02 |title=Life and death of the ground sloth Xibalbaonyx oviceps from the Yucatán Peninsula, Mexico |url=https://www.tandfonline.com/doi/full/10.1080/08912963.2020.1819998 |journal=Historical Biology |language=en |volume=33 |issue=11 |pages=2610–2626 |doi=10.1080/08912963.2020.1819998 |bibcode=2021HBio...33.2610S |issn=0891-2963|url-access=subscription }}</ref> Some authors have suggested ground sloths were largely solitary animals, like living sloths,<ref>{{Cite journal |last1=Borrero |first1=Luis Alberto |last2=Martin |first2=Fabiana María |date=March 2012 |title=Ground sloths and humans in southern Fuego-Patagonia: taphonomy and archaeology |url=http://www.tandfonline.com/doi/abs/10.1080/00438243.2012.646145 |journal=World Archaeology |language=en |volume=44 |issue=1 |pages=102–117 |doi=10.1080/00438243.2012.646145 |issn=0043-8243 |s2cid=86180858|url-access=subscription }}</ref> though other authors have argued that at least some ground sloths are likely to have engaged in gregarious behaviour.<ref>{{Cite journal |last1=Tomassini |first1=Rodrigo L. |last2=Montalvo |first2=Claudia I. |last3=Garrone |first3=Mariana C. |last4=Domingo |first4=Laura |last5=Ferigolo |first5=Jorge |last6=Cruz |first6=Laura E. |last7=Sanz-Pérez |first7=Dánae |last8=Fernández-Jalvo |first8=Yolanda |last9=Cerda |first9=Ignacio A. |date=2020-07-02 |title=Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas |journal=Scientific Reports |language=en |volume=10 |issue=1 |pages=10955 |bibcode=2020NatSR..1010955T |doi=10.1038/s41598-020-67863-0 |issn=2045-2322 |pmc=7331707 |pmid=32616813 |doi-access=free}}</ref> Whether or not ground sloths had a slow [[metabolism]] like living xenarthrans (including living sloths) is debated.<ref name=":6" />

Like living sloths, ground sloths likely only gave birth to a single offspring at a time,<ref>{{Cite journal |last1=Pujos |first1=François |last2=De Iuliis |first2=Gerardo |last3=Vilaboim Santos |first3=Luciano |last4=Cartelle |first4=Cástor |date=2023-07-11 |title=Description of a fetal skeleton of the extinct sloth Nothrotherium maquinense (Xenarthra, Folivora): Ontogenetic and palaeoecological interpretations |url=https://link.springer.com/10.1007/s10914-023-09665-5 |journal=Journal of Mammalian Evolution |language=en |volume=30 |issue=3 |pages=577–595 |doi=10.1007/s10914-023-09665-5 |issn=1064-7554 |s2cid=259892230|url-access=subscription }}</ref><ref name=":3">{{Cite journal |last1=Semken |first1=Holmes A. |last2=Gregory McDonald |first2=H. |last3=Graham |first3=Russell W. |last4=Adrain |first4=Tiffany |last5=Artz |first5=Joe Alan |last6=Baker |first6=Richard G. |last7=Bryk |first7=Alexander B. |last8=Brenzel |first8=David J. |last9=Arthur Bettis |first9=E. |last10=Clack |first10=Andrew A. |last11=Grimm |first11=Brittany L. |last12=Haj |first12=Adel |last13=Horgen |first13=Sarah E. |last14=Mahoney |first14=Meghann C. |last15=Ray |first15=Harold A. |date=2022-06-30 |title=Paleobiology of Jefferson's Ground Sloth ( Megalonyx jeffersonii ) derived from three contemporaneous, ontogenetically distinct individuals recovered from Southwestern Iowa, U.S.A. |journal=Journal of Vertebrate Paleontology |language=en |volume=42 |issue=1 |bibcode=2022JVPal..42E4115S |doi=10.1080/02724634.2022.2124115 |issn=0272-4634 |s2cid=253258474 |doi-access=free}}</ref> with likely several years between the birth of offspring. At least some ground sloths engaged in long-term [[parental care]], with one adult (presumably female) ''Megalonyx'' found with two juveniles of different ages, with the oldest juvenile suggested to be 3–4 years old.<ref name=":3" /> Juvenile ground sloths may have clung to the body of their mother for some time following birth, as occurs in living tree sloths.<ref>{{Cite journal |last=Grass |first=Andy D. |date=2019-01-02 |title=Inferring differential behavior between giant ground sloth adults and juveniles through scapula morphology |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2019.1569018 |journal=Journal of Vertebrate Paleontology |language=en |volume=39 |issue=1 |pages=e1569018 |doi=10.1080/02724634.2019.1569018 |bibcode=2019JVPal..39E9018G |issn=0272-4634|url-access=subscription }}</ref>

== Evolution ==
The earliest unambiguous fossil evidence of ground sloths comes from the early [[Oligocene]].<ref>{{Cite journal |last1=Pujos |first1=François |last2=De Iuliis |first2=Gerardo |last3=Cartelle |first3=Cástor |date=March 2017 |title=A Paleogeographic Overview of Tropical Fossil Sloths: Towards an Understanding of the Origin of Extant Suspensory Sloths? |url=http://link.springer.com/10.1007/s10914-016-9330-4 |journal=Journal of Mammalian Evolution |language=en |volume=24 |issue=1 |pages=19–38 |doi=10.1007/s10914-016-9330-4 |issn=1064-7554|hdl=11336/63466 |hdl-access=free }}</ref> Ground sloths had dispersed into the Caribbean already by 31 million years ago, as evidenced by a femur found in Puerto Rico.<ref name=":5">{{Cite journal |last1=Tejada |first1=Julia V |last2=Antoine |first2=Pierre-Olivier |last3=Münch |first3=Philippe |last4=Billet |first4=Guillaume |last5=Hautier |first5=Lionel |last6=Delsuc |first6=Frédéric |last7=Condamine |first7=Fabien L |date=2023-12-02 |editor-last=Wright |editor-first=April |title=Bayesian Total-Evidence Dating Revisits Sloth Phylogeny and Biogeography: A Cautionary Tale on Morphological Clock Analyses |journal=Systematic Biology |volume=73 |issue=1 |pages=125–139 |language=en |doi=10.1093/sysbio/syad069 |pmid=38041854 |issn=1063-5157|doi-access=free |pmc=11129595 }}</ref> During the [[Miocene]], sloths diversified, with the major families of sloths appearing during this period,<ref name=":5" /> with diversity waxing and waning over the course of the Miocene. Megalonychid and mylodontid sloths had migrated into North America by the Late Miocene, around 10 million years ago. At the end of the Miocene, ground sloth diversity declined, though their diversity would remain largely stable throughout the [[Pliocene]] and [[Pleistocene]] periods, up until their extinction. During the Pliocene and Pleistocene, as part of the [[Great American Interchange]], additional lineages of sloths migrated into Central and North America.<ref>{{Cite journal |last1=Varela |first1=Luciano |last2=Tambusso |first2=P Sebastián |last3=McDonald |first3=H Gregory |last4=Fariña |first4=Richard A |date=2019-03-01 |editor-last=Fieldman |editor-first=Matt |title=Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis |url=https://academic.oup.com/sysbio/article/68/2/204/5098296 |journal=Systematic Biology |language=en |volume=68 |issue=2 |pages=204–218 |doi=10.1093/sysbio/syy058 |pmid=30239971 |issn=1063-5157|url-access=subscription }}</ref> Prior to their extinction, there were over 30 living species of ground sloths across the Americas during the [[Late Pleistocene]].<ref name=":4" />

== Families ==
[[Paleontologist]]s assign more than 80&nbsp;[[genera]] of ground sloths to multiple [[family (biology)|families]].<ref>Modified from McKenna & Bell (1997)</ref>

=== Megalonychidae ===
{{Main|Megalonychidae}}
The [[Megalonychidae|megalonychid]] ground sloths first appeared in the [[Eocene|Late Eocene]], about 35&nbsp;million years ago, in Patagonia. Megalonychids first reached North America by island-hopping, prior to the formation of the [[Isthmus of Panama]]. Some lineages of megalonychids increased in size as time progressed. The first species of these were small and may have been partly tree-dwelling, whereas the [[Pliocene]] (about 5 to 2&nbsp;million years ago) species were already approximately half the size of the huge [[Late Pleistocene]] ''[[Megalonyx jeffersonii]]'' from the [[Quaternary glaciation|last ice age]]. Some West Indian island species were as small as a large cat; their dwarf condition typified both tropical adaptation and their restricted island environment.  This small size also enabled them a degree of arboreality.<ref name="J.L. White 1993">J.L. White (1993)</ref>

''[[Megalonyx]]'', which means "giant claw", was a widespread North American genus that lived past the close of the [[Last glacial period|last (Wisconsin) glaciation]], when so many large mammals died out.  Remains have been found as far north as Alaska<ref>{{cite journal |last=Stock |first=C. |title=A ground sloth in Alaska |journal=[[Science (journal)|Science]] | volume = 95 |issue = 2474 |pages = 552–553 |publisher=[[American Association for the Advancement of Science|AAAS]] |date=29 May 1942 |doi=10.1126/science.95.2474.552 |pmid=17790868 |bibcode=1942Sci....95..552S }}<!--| access-date = 10 October 2009--></ref> and the [[Yukon]].<ref name=Harrington/><ref>{{cite journal | last = McDonald | first = H.G. | author2 = Harington, C.R. | author3 = de&nbsp;Iuliis, G. | title = The Ground Sloth Megalonyx from Pleistocene Deposits of the Old Crow Basin, Yukon, Canada | journal = Arctic | volume = 53 | issue = 3 | pages = 213–220 | publisher = The Arctic Institute of North America | location = Calgary, Alberta | date = September 2000 | url = http://pubs.aina.ucalgary.ca/arctic/Arctic53-3-213.pdf | access-date = 16 August 2008 | doi = 10.14430/arctic852 | archive-date = 3 July 2020 | archive-url = https://web.archive.org/web/20200703013709/http://pubs.aina.ucalgary.ca/arctic/Arctic53-3-213.pdf | url-status = dead }}</ref> Ongoing excavations at Tarkio Valley in southwestern [[Iowa]] may reveal something of the familial life of ''Megalonyx''. An adult was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations.<ref>Semken and Brenzel, http://slothcentral.com/?page_id=2 {{Webarchive|url=https://web.archive.org/web/20090101073804/http://slothcentral.com/?page_id=2 |date=2009-01-01 }}</ref><ref>{{cite journal | last1 = Semken | last2 = Brenzel | year = 2007 | title = One Sloth Becomes Three | journal=Newsletter of the Iowa Archeological Society | volume = 57 | page = 1 }}</ref>

The earliest known North American megalonychid, ''[[Pliometanastes|Pliometanastes protistus]]'', lived in the southern U.S. about 9&nbsp;million years ago and is believed to have been the predecessor of ''Megalonyx''. Several species of ''Megalonyx'' have been named; in fact it has been stated that "nearly every good specimen has been described as a different species".<ref name=Harrington>Harrington (1993)</ref> A broader perspective on the group, accounting for age, sex, individual and geographic differences, indicates that only three species are valid (''M. leptostomus'', ''M. wheatleyi'', and ''M. jeffersonii'') in the late Pliocene and Pleistocene of North America,<ref>Kurtén & Anderson, 1980, p. 136.</ref> although work by McDonald lists five species.
Jefferson's ground sloth has a special place in modern [[paleontology]], for [[Thomas Jefferson]]'s letter on ''Megalonyx'', read before the [[American Philosophical Society]] of [[Philadelphia]] in August&nbsp;1796, marked the beginning of [[vertebrate]] paleontology in North America.<ref name=Harrington/> When [[Lewis and Clark]] set out, Jefferson instructed Meriwether Lewis to keep an eye out for ground sloths. He was hoping they would find some living in the Western range. ''Megalonyx jeffersonii'' was appropriately named after Thomas Jefferson.<ref name=Harrington/>

=== Megatheriidae ===
{{Main|Megatheriidae}}
[[Image:Eremotherium.jpg|thumb|right|Fossil ''[[Eremotherium]]'' skeleton, [[National Museum of Natural History]], Washington, DC.]]
The [[Megatheriidae|megatheriid]] ground sloths are relatives of the megalonychids; these two families, along with the family Nothrotheriidae, form the [[infraorder]] [[Megatheria]]. Megatheriids appeared later in the Oligocene, some 30&nbsp;million years ago, also in South America. The group includes the heavily built ''[[Megatherium]]'' (given its name 'great beast' by [[Georges Cuvier]]<ref>G. Cuvier (1796)</ref>) and ''[[Eremotherium]],'' which are the largest known ground sloths, thought to have had body masses of 3.5-4 tons.<ref name=":4">{{Cite journal |last=McDonald |first=H. Gregory |date=2023-06-06 |title=A Tale of Two Continents (and a Few Islands): Ecology and Distribution of Late Pleistocene Sloths |journal=Land |language=en |volume=12 |issue=6 |pages=1192 |doi=10.3390/land12061192 |issn=2073-445X|doi-access=free }}</ref> 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 ''Eremotherium eomigrans'' which arrived 2.2&nbsp;million years ago, after crossing the recently formed [[Panama]]nian land bridge. With more than five tons in weight, 6&nbsp;meters in length, and able to reach as high as {{convert|17|ft|m}}, it was larger 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 a foot long.<ref>De Iuliis and Cartelle (1999)</ref>

===Nothrotheriidae===
{{Main|Nothrotheriidae}}
Recently recognized, ground sloths of [[Nothrotheriidae]] are often associated with those of the [[Megatheriidae]], and together the two form the superfamily Megatherioidea. The most prominent members of the group are the South American genus ''[[Thalassocnus]]'', known for being aquatic, and ''[[Nothrotheriops]]'' from North America.

The last ground sloths in North America belonging to ''Nothrotheriops'' died so recently that their [[subfossil]] dung has remained undisturbed in some caves. One of the skeletons, found in a [[lava tube]] (cave) at [[Aden Crater]], adjacent to [[Kilbourne Hole]], [[New Mexico]], still had skin and hair preserved, and is now at the Yale [[Peabody Museum of Natural History|Peabody Museum]]. The largest samples of ''Nothrotheriops'' dung can be found in the collections of the Smithsonian Museum. Another ''Nothrotheriops'' was excavated at [[Shelter Cave]], also in [[Doña Ana County]], [[New Mexico]].{{citation needed|date=May 2014}}

=== Mylodontidae ===
{{Main|Mylodontidae}}
[[File:Paramylodon fossil at Texas Memorial Museum.jpg|thumb|right|''[[Paramylodon harlani]]'', [[Texas Memorial Museum]], [[University of Texas at Austin]]]]
The [[Mylodontidae|mylodontid]] ground sloths together with their relatives the scelidotheriids form the [[Mylodontoidea]], the second radiation of ground sloths. The discovery of their fossils in caverns associated with human occupation led some early researchers to theorize that the early humans built [[corral]]s when they could procure a young ground sloth, to raise the animal to butchering size.<ref>A. S. Woodward (1900)</ref> However, radiocarbon dates do not support simultaneous occupation of the site by humans and sloths.<ref name = "explained">{{cite journal | last = Naish | first = Darren | title = Fossils explained 51: Sloths | journal=Geology Today | volume = 21 | issue = 6 | pages = 232–238 | publisher=[[Geologists' Association]], [[Geological Society of London]] and [[Blackwell Publishing]] | date = 28 Nov 2005 | url = http://www3.interscience.wiley.com/journal/118652140/abstract | archive-url = https://archive.today/20121008120854/http://www3.interscience.wiley.com/journal/118652140/abstract | url-status = dead | archive-date = 8 October 2012 | doi = 10.1111/j.1365-2451.2005.00538.x  | s2cid = 85808869 | access-date = 29 January 2009| url-access = subscription }}</ref> [[Subfossil]] remains like coproliths, fur and skin have been discovered in some quantities. The [[American Museum of Natural History]] has exhibited a sample of ''[[Mylodon]]'' dung from Argentina with a note that reads "deposited by [[Theodore Roosevelt]]".<ref name="Bell2002">{{cite journal |last=Bell |first=C.M. |title=Did elephants hang from trees? - the giant sloths of South America |journal=Geology Today |volume=18 |issue=2 |year=2002 |pages=63–66 (see p.&nbsp;66) |doi=10.1046/j.1365-2451.2002.00334.x|bibcode=2002GeolT..18...63B |s2cid=130426084 }}</ref><ref name = "TRCenter">{{cite web |url= https://www.theodorerooseveltcenter.org/Research/Digital-Library/Record?libID=o211307|title= Letter from Theodore Roosevelt to George Herbert Sherwood|last= Roosevelt|first= T.R.|date= 1915-01-04|website= theodorerooseveltcenter.org|publisher= [[Dickinson State University]]|access-date= 2019-10-12}}</ref><ref name = "AMNH">{{cite web |url= https://www.amnh.org/exhibitions/permanent/south-american-peoples/roosevelt-collection |title= Roosevelt Collections |website= amnh.org/exhibitions |publisher=[[American Museum of Natural History]] |access-date=2019-10-12}}</ref><ref name= "Warren2015">{{cite web |url=https://www.davidwarrenonline.com/2015/05/28/the-ground-sloth/ |title=The ground sloth |last=Warren |first=D. |date=2016-05-28 |website=Essays in Idleness |access-date= 2019-10-12}}</ref> Mylodontids are the only ground sloths confirmed to have had [[osteoderms]] embedded within their skin, though osteoderms were only present in a handful of genera and absent in many others.<ref>{{Cite journal |last=McDonald |first=H. Gregory |date=December 2018 |title=An Overview of the Presence of Osteoderms in Sloths: Implications for Osteoderms as a Plesiomorphic Character of the Xenarthra |url=http://link.springer.com/10.1007/s10914-017-9415-8 |journal=Journal of Mammalian Evolution |language=en |volume=25 |issue=4 |pages=485–493 |doi=10.1007/s10914-017-9415-8 |s2cid=254697023 |issn=1064-7554|url-access=subscription }}</ref>

The largest mylodontid is ''[[Lestodon]]'', with an estimated mass of {{Convert|3400-4100|kg|lb}}.<ref>{{Cite journal |last1=Tomassini |first1=Rodrigo L. |last2=Montalvo |first2=Claudia I. |last3=Garrone |first3=Mariana C. |last4=Domingo |first4=Laura |last5=Ferigolo |first5=Jorge |last6=Cruz |first6=Laura E. |last7=Sanz-Pérez |first7=Dánae |last8=Fernández-Jalvo |first8=Yolanda |last9=Cerda |first9=Ignacio A. |date=2020-07-02 |title=Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas |journal=Scientific Reports |language=en |volume=10 |issue=1 |page=10955 |doi=10.1038/s41598-020-67863-0 |pmid=32616813 |pmc=7331707 |bibcode=2020NatSR..1010955T |issn=2045-2322|hdl=10261/233402 |hdl-access=free }}</ref>

=== Scelidotheriidae ===
{{Main|Scelidotheriidae}}
The ground sloth family [[Scelidotheriidae]] was demoted in 1995 to the subfamily Scelidotheriinae within Mylodontidae.<ref>{{cite web |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=83047 |website=PaleoBiology Database |title=Scelidotheriinae, basic info}}</ref><ref name="Gaudin_1995">{{cite journal |last=Gaudin |first=T.J. |date=1995-09-14 |title=The Ear Region of Edentates and the Phylogeny of the Tardigrada (Mammalia, Xenarthra) |journal=Journal of Vertebrate Paleontology |volume=15 |issue=3 |pages=672–705 |doi=10.1080/02724634.1995.10011255 |jstor=4523658|bibcode=1995JVPal..15..672G }}<!--| access-date = 2013-06-19 --></ref> Based on collagen sequence data showing that its members are more distant from other mylodontids than [[Choloepodidae]], it was elevated back to full family status in 2019.<ref name="Presslee2019" /> Together with Mylodontidae, the enigmatic ''[[Pseudoprepotherium]]'' and [[two-toed sloth]]s, the scelidotheriids form the superfamily Mylodontoidea. ''[[Chubutherium]]'' is an ancestral and very plesiomorphic member of this subfamily and does not belong to the main group of closely related genera, which include ''[[Scelidotherium]]'' and ''[[Catonyx]]''.

===Phylogeny===
The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig.&nbsp;4 of Presslee ''et al.''., 2019).<ref name="Presslee2019">{{cite journal |last1= Presslee |first1=S. |last2= Slater |first2=G.J. |last3= Pujos |first3=F. |last4=Forasiepi |first4=A.M. |last5=Fischer |first5=R. |last6=Molloy |first6=K. |last7=Mackie |first7=M. |last8=Olsen |first8=J.V. |last9= Kramarz |first9=A. |last10=Taglioretti |first10=M. |last11=Scaglia |first11=F. |last12=Lezcano |first12=M. |last13=Lanata |first13=J.L. |last14= Southon |first14= J. |last15= Feranec |first15= R. |last16= Bloch |first16= J. |last17= Hajduk |first17= A. |last18= Martin |first18=F.M. |last19= Gismondi |first19=R.S. |last20= Reguero |first20=M. |last21=de&nbsp;Muizon |first21= C. |last22= Greenwood |first22= A. |last23= Chait |first23=B.T. |last24= Penkman |first24= K. |author24-link= Kirsty Penkman |last25= Collins |first25= M. |last26= MacPhee |first26= R.D.E. |display-authors=6 |title= Palaeoproteomics resolves sloth relationships |journal=Nature Ecology & Evolution |volume= 3 |issue= 7 |pages= 1121–1130 |year= 2019 |doi= 10.1038/s41559-019-0909-z |pmid= 31171860 |bibcode=2019NatEE...3.1121P |s2cid= 174813630 |url= http://eprints.whiterose.ac.uk/147061/1/5426_3_merged_1554730549.pdf}}</ref>

{{clade | style = font-size: 100%;line-height:100%
| label1 =[[Folivora]]
|1={{clade
  |label1={{extinct}} [[Megalocnidae]]
  |sublabel1={{small|(Caribbean sloths)}}
  |1={{clade
    |1={{extinct}} ''[[Neocnus|Neocnus dousman]]''
    |2={{clade
      |1={{clade
        |1={{extinct}} ''[[Parocnus|Parocnus serus]]''
        |2={{extinct}} ''[[Neocnus|Neocnus comes]]''
      }}
      |2={{extinct}} ''[[Acratocnus|Acratocnus ye]]''
    }}
  }}
  |2={{clade
    |1={{clade
      |label1=Megatherioidea
 <!-- |grouplabelstyle1=vertical-align:left;
      |grouplabel1={{clade label|'''Megatherioidea'''|color=red|width=8em}}
      |bar1=red   -->
      |1={{clade
        |1={{clade
          |label1 ={{extinct}} [[Nothrotheriidae]]
          |1={{extinct}} ''[[Nothrotheriops shastensis]]''
          |label2 ={{extinct}} [[Megatheriidae]]
          |2={{extinct}} ''[[Megatherium americanum]]''
        }}
        |2={{clade
          |label1 ={{extinct}} [[Megalonychidae]]
          |1={{extinct}} ''[[Megalonyx jeffersoni]]''
          |label2 =[[Bradypodidae]]
          |sublabel2 = {{small| (three-fingered sloths) }}
          |2=[[Bradypodidae|5&nbsp;living spp.]]
        }}
      }}
      |label2=Mylodontoidea
 <!-- |grouplabel2={{clade label|'''Mylodontoidea'''|color=green|width=7.5em}}
      |bar2=green  --> 
      |2={{clade
        |1={{clade
          |label1 ={{extinct}} [[Scelidotheriidae]]
          |1={{clade
            |1={{extinct}} ''[[Scelidotherium]]'' sp.
            |2={{extinct}} ''[[Scelidodon]]'' sp.
          }}
        }}
        |2={{clade
          |label1 =[[Choloepodidae]]
          |sublabel1={{small| (two-fingered sloths) }}
          |1=[[Choloepodidae|2&nbsp;living spp.]]
          |label2 ={{extinct}} [[Mylodontidae]]
          |2={{clade
            |1={{extinct}} ''[[Lestodon armatus]]''
            |2={{clade
              |1={{extinct}} ''[[Paramylodon harlani]]''
               |2={{clade
                |1={{extinct}} ''[[Mylodon darwinii]]''
                |2={{extinct}} ''[[Glossotherium|Glossotherium robustus]]''
              }}
            }}
          }}
        }}
      }}
    }}
  }}
}}
}}

== Extinction ==
[[Image:TamanduaStanding.jpg|thumb|right|A ''[[Tamandua]]'' anteater in an upright defensive stance similar to those presumed to have been adopted by ground sloths, per trackways preserved in New Mexico]]
[[File:Rampart Cave interior sloth dung.jpg|thumb|left|[[Subfossil]]ized ''[[Nothrotheriops]] shastensis'' dung in Rampart Cave, [[Arizona]] ([[National Park Service|NPS]], 1938)]]


Radiocarbon dating places the disappearance of ground sloths in what is now the United States at around 11,000&nbsp;years ago. The Shasta ground sloth (''[[Nothrotheriops]] shastensis'') visited Rampart Cave (located on the [[Arizona]] side of the [[Lake Mead National Recreation Area]]) seasonally, leaving behind a massive stratified [[subfossil]]ized dung deposit, and seemed to be flourishing from 13,000 until 11,000&nbsp;BP, when the deposition suddenly stopped.<ref name="Martin">{{cite book |last=Martin |first=P.S. |author-link=Paul Schultz Martin |title=Twilight of the Mammoths: Ice Age extinctions and the rewilding of America
 | publisher = [[University of California Press]] | year = 2005 
 | chapter = Chapter 4. Ground Sloths at Home | pages = 85–87
 | url = https://books.google.com/books?id=gfpla1OY268C
 | chapter-url = https://books.google.com/books?id=gfpla1OY268C&pg=PA85
 | isbn = 0-520-23141-4 |oclc= 58055404 | access-date= 2018-04-29}}</ref> Steadman ''et al.'' argue that it is no coincidence that studies have shown that ground sloths disappeared from an area a few years after the arrival of humans.<ref name="Steadman_2005" /> [[Fossil track|Trackways]] preserved in New Mexico (probably dating from 10 to 15.6&nbsp;thousand years ago) that appear to show a group of humans chasing or harassing three ''[[Nothrotheriops shastensis|Nothrotheriops]]'' or ''[[Paramylodon harlani|Paramylodon]]'' ground sloths may record the scene of a hunt. The tracks are interpreted as showing seven instances of a sloth turning and rearing up on its hind legs to confront its pursuers, while the humans approach from multiple directions, possibly in an attempt to distract it.<ref name="Garisto2018">{{cite web |url =https://www.sciencenews.org/article/footprints-prove-humans-hunted-giant-sloths-during-ice-age |title =Footprints prove humans hunted giant sloths during the Ice Age |last =Garisto |first =D.|date =2018-04-25 |website=[[Science News]] |publisher=Society for Science & the Public |access-date=2018-04-26}}</ref><ref name="Stock2018">{{cite web |url= https://www.reuters.com/article/us-science-giant-sloth/giant-sloth-vs-ancient-man-fossil-footprints-track-prehistoric-hunt-idUSKBN1HW2L0 |title=Giant sloth vs. ancient man: fossil footprints track prehistoric hunt |last= Stock |first= M. |date=2018-04-25 |website=Reuters.com |access-date=2018-04-27}}</ref><ref name="Bustos2018">{{cite journal |last1=Bustos |first1=D. |last2=Jakeway |first2=J. |last3=Urban |first3=T.M. |last4=Holliday |first4=V.T.|last5=Fenerty |first5=B.|last6= Raichlen|first6=D.A. |last7=Budka |first7=M. |last8=Reynolds |first8=S.C. |last9= Allen |first9=B.D. |last10=Love |first10=D.W. |last11=Santucci |first11=V.L. |last12=Odess |first12=D. |last13=Willey |first13=P. |last14=McDonald |first14=H.G. |last15=Bennett |first15=M.R. |title=Footprints preserve terminal Pleistocene hunt? Human-sloth interactions in North America |journal=Science Advances |volume=4 |issue=4 |date=2018-04-25 |pages=eaar7621 |doi=10.1126/sciadv.aar7621 |pmid=29707640 |pmc=5916513 |bibcode=2018SciA....4.7621B}}</ref>

Those who argue in favor of humans being the direct cause of the ground sloths' extinction point out that the few sloths that remain are small sloths that spend most of their time in trees, making it difficult for them to be spotted. Although these sloths were well hidden, they still would have been affected by the climate changes that others claim wiped out the ground sloths. Additionally, after the continental ground sloths disappeared, [[Pilosans of the Caribbean|insular sloths of the Caribbean]] survived for approximately 6,000 years longer, which correlates with the fact that these islands were not colonized by humans until about 5500 yr BP.<ref name = "Steadman_2005"/>

It is difficult to find evidence that supports either claim on whether humans hunted the ground sloths to extinction.<ref>{{cite journal |url=https://pdfs.semanticscholar.org/93ff/3f5e8838d037cbd02f9e27a7707ae47848ad.pdf |archive-url=https://web.archive.org/web/20170202042353/https://pdfs.semanticscholar.org/93ff/3f5e8838d037cbd02f9e27a7707ae47848ad.pdf |url-status=dead |archive-date=2017-02-02 |title=Combination of humans, climate, and vegetation change triggered Late Quaternary megafauna extinction in the Última Esperanza region, southern Patagonia, Chile |last1=Villavicencio |first1=N.A. |display-authors=etal |journal=Ecography |volume=39 |issue=2 |pages=125–140 |year=2016 |doi=10.1111/ecog.01606|bibcode=2016Ecogr..39..125V |s2cid=16109915 }}</ref> Removing large amounts of meat from large mammals such as the ground sloth requires no contact with the bones; tool-inflicted damage to bones is a key sign of human interaction with the animal.<ref name="Borrero2012">{{cite journal |last1=Borrero |first1=L.A. |last2=Martin |first2=F.M. |title=Ground sloths and humans in southern Fuego-Patagonia: Taphonomy and archaeology |journal=World Archaeology |volume=44 |issue=1 |year=2012 |pages=102–117 |doi=10.1080/00438243.2012.646145 |s2cid=86180858}}</ref>

=== Hunting of ground sloths ===

==== Kill sites ====
A number of kill sites are known for ground sloths in the Americas, these include Campo Laborde in the Pampas of Argentina, where an individual of ''[[Megatherium americanum]]'' was butchered at the edge of a swamp, dating to approximately 12,600 years [[Before Present]] (BP),<ref name=":0">{{Cite journal |last1=Politis |first1=Gustavo G. |last2=Messineo |first2=Pablo G. |last3=Stafford |first3=Thomas W. |last4=Lindsey |first4=Emily L. |date=March 2019 |title=Campo Laborde: A Late Pleistocene giant ground sloth kill and butchering site in the Pampas |journal=Science Advances |language=en |volume=5 |issue=3 |pages=eaau4546 |bibcode=2019SciA....5.4546P |doi=10.1126/sciadv.aau4546 |issn=2375-2548 |pmc=6402857 |pmid=30854426}}</ref> with another potential ''Megatherium'' kill site being Arroyo Seco 2 in the same region, dating to approximately 14,782–11,142 cal yr BP.<ref name=":2" /> In northern Ohio, a ''[[Megalonyx jeffersoni]]'' skeleton dubbed the "Firelands Ground Sloth" has cut marks indicative of butchery, dating to 13,738 to 13,435 years BP.<ref name=":1">{{Cite journal |last1=Redmond |first1=Brian G. |last2=McDonald |first2=H Gregory |last3=Greenfield |first3=Haskel J. |last4=Burr |first4=Matthew L. |date=March 2012 |title=New evidence for Late Pleistocene human exploitation of Jefferson's Ground Sloth ( Megalonyx jeffersonii ) from northern Ohio, USA |url=http://www.tandfonline.com/doi/abs/10.1080/00438243.2012.647576 |journal=World Archaeology |language=en |volume=44 |issue=1 |pages=75–101 |doi=10.1080/00438243.2012.647576 |s2cid=161436888 |issn=0043-8243|url-access=subscription }}</ref> At the Santa Elina rockshelter in Mato Grosso Brazil, a specimen of ''[[Glossotherium]]'' is associated with hearths and stone tools, dating to 11,833–11,804 years BP. At [[Cueva Fell|Fell's Cave]] in southern Chilean Patagonia, a specimen of ''[[Mylodon]]'' with fractured and burned bones associated with human activity has been dated to approximately 12,766–12,354 years BP.<ref name=":2">{{Cite journal |last1=Bampi |first1=Hugo |last2=Barberi |first2=Maira |last3=Lima-Ribeiro |first3=Matheus S. |date=December 2022 |title=Megafauna kill sites in South America: A critical review |url=https://linkinghub.elsevier.com/retrieve/pii/S0277379122004826 |journal=Quaternary Science Reviews |language=en |volume=298 |pages=107851 |doi=10.1016/j.quascirev.2022.107851|bibcode=2022QSRv..29807851B |s2cid=253876769 |url-access=subscription }}</ref>

==== Hunting weapons ====
Humans are believed to have entered the New World via [[Beringia]], a [[land bridge]] which connected Asia and North America during the [[last glacial maximum]]. Mosimann and Martin (1975) suggested the first of these nomads descended from hunting families who had acquired the skills to track down and kill large mammals.<ref name=Mosimann1975>{{cite journal |last1=Mosimann |first1=J.E. |last2= Martin |first2=P.S. |title= Simulating overkill by paleoindians: Did man hunt the giant mammals of the New World to extinction? Mathematical models show that the hypothesis is feasible |journal= American Scientist |volume= 63 |issue= 3 |pages= 304–313 |date= May–June 1975 |jstor= 27845466}}</ref> By this time, humans had developed proficient hunting weapons, including the [[Clovis point]]s, which were narrow, carved stone projectiles used specifically for big game. A couple of hundred years later, the [[atlatl]] became widely used, which allowed them to throw spears with greater velocity.<ref name="Raymond1986">{{cite journal |last1= Raymond |first1= A. |title= Experiments in the function and performance of the weighted atlatl |journal= World Archaeology |volume= 18 |issue= 2 |year= 1986 |pages= 153–177 |doi= 10.1080/00438243.1986.9979996 |s2cid= 56904522 }}</ref> These inventions would have allowed hunters to put distance between them and their prey, potentially making it less dangerous to approach ground sloths.

==== Advantages ====
Certain characteristics and behavioral traits of the ground sloths made them easy targets for human hunting and provided hunter-gatherers with strong incentives to hunt these large mammals.

Ground sloths often fed in open fields.<ref name=Bargo2001>{{cite journal |last1= Bargo |first1= M.S. |title= The ground sloth ''Megatherium americanum'': Skull shape, bite forces, and diet |journal= Acta Palaeontologica Polonica |volume= 46 |issue= 2 |pages= 173–192 |date= 2001 |url= http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.agro-article-0182ea1c-9b11-41d8-97d3-d8fa70cf98e4/c/app46-173.pdf |access-date= 2019-03-21}}</ref> Recent studies have attempted to discover the diet of ground sloths through fossils of their dung. Analysis of these [[coprolite|coproliths]] have found that ground sloths often ate the foliage of trees, hard grasses, shrubs, and yucca; these plants were located in areas that would have exposed them,<ref name="Poinar1998">{{cite journal |last1=Poinar |first1=H.N. |last2=Hofreiter |first2=M. |last3=Spaulding |first3=W.G. |last4=Martin |first4=P.S. |last5=Stankiewicz |first5=B.A. |last6= Bland |first6=H. |last7=Evershed |first7=R.P. |last8=Possnert |first8=G. |last9=Pääbo |first9=S. |title=Molecular coproscopy: Dung and diet of the extinct ground sloth ''Nothrotheriops shastensis'' |journal= Science |volume= 281 |issue= 5375 |year= 1998 |pages= 402–406 |doi=10.1126/science.281.5375.402 |bibcode=1998Sci...281..402P |pmid=9665881 |s2cid=7577657}}</ref> making them susceptible to human predation. Ground sloths were not only easy to spot, but had never interacted with humans before, so would not have known how to react to them. Additionally, these large mammals waddled on their hind legs and front knuckles, keeping their claws turned in. Their movement and massive build (some weighed up to {{convert|3000|kg}}) imply they were relatively slow mammals.<ref name=Steadman_2005/>

These reasonable after-the-fact inferences from the evidence might explain why ground sloths would have been easy prey for hunters, but are not certain.<ref name="Martin2005">{{cite book |last=Martin |first=P.S. |author-link=Paul Schultz Martin |title=Twilight of the Mammoths: Ice Age extinctions and the rewilding of America |year=2005 |publisher=[[University of California Press]] |isbn=0-520-23141-4 |url=https://archive.org/details/twilightofmammot00paul |url-access=registration |oclc=58055404 |access-date=11 September 2014 |pages=[https://archive.org/details/twilightofmammot00paul/page/33 33], 87, 139}}</ref>

==== Difficulties ====
While ground sloths would have been relatively easy to spot and approach, big game hunters' weapons would have been useless from farther than {{convert|30|ft|order=flip}} away. It would have been difficult to take down a ground sloth with a spear-thrower and would have required extensive knowledge of the species. Additionally, the ground sloths' already thick hide was fortified by [[osteoderm]]s, making it difficult to penetrate.<ref name=Borrero2012/><ref>{{cite web |last=Naish |first=Darren |date=30 August 2012 |title=The anatomy of sloths |website=Scientific American |url=https://blogs.scientificamerican.com/tetrapod-zoology/the-anatomy-of-sloths/ |access-date=25 October 2020}}</ref>

Since ground sloths thrived in an environment filled with large predators, they evidently would have been able to also defend themselves against human predation, so there is no reason to expect that they would have been "easy pickings". When feeding, they had enough strength to use their long, sharp claws to tear apart tree branches; presumably their strength and formidable claws would be dangerous for hunters that attempted to attack them at close quarters.<ref>{{cite book |last=Lull |first=Richard S. |author-link=Richard Swann Lull |year=1931 |title=Fossils: What they tell us of plants and animals of the past |publisher=University Society |location=New York, NY |url=https://archive.org/details/fossilswhattheyt031633mbp/page/n19/mode/2up?q=ground+sloth}}</ref> But fossilized evidence of humans hunting on ground sloth in [[White Sands National Park]] suggests that the slow-moving giant sloths were likely easy prey for early humans possibly hurling spears.<ref name="Garisto2018"></ref><ref name="Stock2018"></ref>

==References==
{{Reflist|25em}}

==Sources==
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 | journal = Magasin encyopédique, ou Journal des Sciences, des Lettres et des Arts
 | volume = 1 | pages = 303–310
}}; (2): 227–228.

* {{cite journal
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 | title = A new giant megatheriine ground sloth (Mammalia: Xenarthra: Megatheriidae) from the late Blancan to early Irvingtonian of Florida
 | journal = [[Zoological Journal of the Linnean Society]]
 | volume = 127 | issue = 4| pages = 495–515
 | doi = 10.1111/j.1096-3642.1999.tb01383.x | doi-access = free
}}

* Harrington, C.R. (1993): [https://web.archive.org/web/20031206051103/http://www.beringia.com/02/02maina1.html Yukon Beringia Interpretive Center – Jefferson's Ground Sloth]. Retrieved 2008-JAN-24.
* Hogan, C.M. (2008): [http://www.megalithic.co.uk/article.php?sid=18820 ''Cueva del Milodon'', Megalithic Portal]. Retrieved 2008-APR-13
* Kurtén, Björn and Anderson, Elaine (1980): ''Pleistocene Mammals of North America.'' Columbia University Press, New York. {{ISBN|0-231-03733-3}}
* McKenna, Malcolm C. & Bell, Susan K. (1997): ''Classification of Mammals Above the Species Level.'' Columbia University Press, New York. {{ISBN|0-231-11013-8}}
* Nowak, R.M. (1999): ''Walker's Mammals of the World'' (Vol. 2). Johns Hopkins University Press, London.
* {{cite journal
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| bibcode = 1993JVPal..13..230W
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* {{Cite book
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*{{cite journal
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Borrero and Martin 2012 [broken citation]
Mosimann and Martin 1975 [broken citation]
Raymond 1986[broken citation]
Hawkes et al. 1991 [broken citation]
Bargo 2001 [broken citation]
Poinar et al. 1998 [broken citation]
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== External links ==
{{Commons category}}
*[https://web.archive.org/web/20160915192853/http://libs.uga.edu/science/southpawsloth.html Picture and information about a ground sloth skeleton on display at the University of Georgia's Science Library.]
*[https://web.archive.org/web/20060823122149/http://www.acnatsci.org/museum/leidy/paleo/megalonyx.html Academy of Natural Sciences ground sloth page.]
*[http://www.museum.state.il.us/exhibits/larson/sloth.html Illinois State Museum ground sloth page.]
*[https://web.archive.org/web/20040206222938/http://www.tarpits.org/education/guide/flora/sloth.html Ground sloths at La Brea.]
*[https://web.archive.org/web/20121215052600/http://news.ufl.edu/2000/06/20/sloth/ ''Eremotherium'' in Florida.]
*[http://unmuseum.mus.pa.us/sloth.htm Have some ground sloths survived in Argentina?]
*[https://web.archive.org/web/20031206051103/http://www.beringia.com/02/02maina1.html Ground sloths in general.]
*[http://www.westerncentermuseum.org Western Center for Archaeology and Paleontology] Hemet, CA

{{Taxonbar|from=Q933583}}

[[Category:Clawed herbivores]]
[[Category:Eocene first appearances]]
[[Category:Mammal common names]]
[[Category:Miocene xenarthrans]]
[[Category:Oligocene xenarthrans]]
[[Category:Pleistocene xenarthrans]]
[[Category:Pliocene xenarthrans]]
[[Category:Prehistoric mammals of South America]]
[[Category:Prehistoric mammals of North America]]
[[Category:Prehistoric sloths]]