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{{Short description|Group of tree dwelling mammals noted for slowness}}
{{About|the Central and South American mammal|the cardinal sin|Sloth (deadly sin)|other uses|Sloth (disambiguation)}}
{{Pp-protected|reason=vandalism/disruptive editing|expiry=indefinite|small=yes}}
{{Pp-move-indef|small=yes}}
{{Use dmy dates|date=October 2020}}
{{Automatic taxobox
| name = Sloths<ref name=msw3>{{MSW3 Gardner|pages=100–101|id=11800002}}</ref>
| fossil_range = [[Early Oligocene]] to [[Holocene]]
| image = Bicho-preguiça 3.jpg
| image_caption = ''[[Bradypus variegatus]]'', a [[three-toed sloth]]
| image2 = Choloepus hoffmanni (Puerto Viejo, CR) crop.jpg
| image2_caption = ''[[Choloepus hoffmanni]]'', a [[two-toed sloth]]
| display_parents = 2
| taxon = Folivora
| authority = Delsuc, Catzeflis, Stanhope, and Douzery, 2001<ref name="Delsuc2001"/>
| subdivision_ranks = Families
| subdivision = * †[[Megalocnidae]]
*'''Megatherioidea'''
** †''[[Hiskatherium]]''
** †''[[Similhapalops]]''
** [[Three-toed sloth|Bradypodidae]]
** †[[Megalonychidae]]
** †'''Megatheria'''
*** †[[Megatheriidae]]
*** †[[Nothrotheriidae]]
*'''Mylodontoidea'''
** [[Choloepodidae]]
** †[[Mylodontidae]]
** †[[Scelidotheriidae]]
| range_map = Sloth range.jpg
| range_map_caption = Red: two-toed sloth, blue: three-toed sloth, purple: both two-toed sloth and three-toed sloth
| synonyms = * Tardigrada <small>Latham & Davies, 1795</small>
* [[Phyllophaga (mammal)|Phyllophaga]] <small>Owen, 1842</small>
}}
[[File:Three-toed sloth crossing road in Costa Rica.jpg|alt=Sloth |thumb|Three-toed sloth crossing a road in Costa Rica]]
'''Sloths''' are a [[Neotropical realm|Neotropical]] group of [[xenarthra]]n [[mammal]]s constituting the suborder '''Folivora''', including the extant [[Arboreal locomotion|arboreal]] tree sloths and extinct terrestrial [[ground sloth]]s. Noted for their slowness of movement, tree sloths spend most of their lives hanging upside down in the trees of the [[tropical rainforest]]s of [[South America]] and [[Central America]]. Sloths are considered to be most closely related to [[anteater]]s, together making up the xenarthran order [[Pilosa]].

There are six extant sloth [[species]] in two [[genera]] – ''[[Bradypus]]'' (three-toed sloths) and ''[[Choloepus]]'' (two-toed sloths). Despite this traditional naming, all sloths have three toes on each rear limb – although two-toed sloths have only two digits on each forelimb.<ref name="scf">{{cite web |title=Overview |url=http://slothconservation.com/about-the-sloth/overview/ |publisher=The Sloth Conservation Foundation |access-date=29 November 2017 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201031042/http://slothconservation.com/about-the-sloth/overview/ |url-status=live }}</ref> The two groups of sloths are from different, distantly related families, and are thought to have evolved their morphology via [[parallel evolution]] from terrestrial ancestors. Besides the extant species, many species of ground sloths ranging up to the size of elephants (like ''[[Megatherium]]'') inhabited both North and South America during the [[Pleistocene]] Epoch. However, they became extinct during the [[Quaternary extinction event]] around 12,000 years ago, along with most large animals across the Americas. The extinction correlates in time with the arrival of humans, but [[Climate variability and change|climate change]] has also been suggested to have contributed. Members of an endemic [[Evolutionary radiation|radiation]] of [[Megalocnidae|Caribbean sloths]] also formerly lived in the [[Greater Antilles]] but became extinct after humans settled the archipelago in the mid-Holocene, around 6,000 years ago.

Sloths are so named because of their very low metabolism and deliberate movements. ''Sloth'', related to ''slow'', literally means "laziness", and their common names in several other languages (e.g. {{langx|de|Faultier}}, {{langx|fr|paresseux}}, {{langx|es|perezoso}}, {{langx|pt|preguiça}}, [[Romanian language|Romanian]]: ''leneș'', [[Finnish language|Finnish]]: ''laiskiainen'') also mean "lazy" or similar. Their slowness permits their low-energy diet of leaves and avoids detection by predatory hawks and cats that hunt by sight.<ref name="scf"/> Sloths are almost helpless on the ground but are able to swim.<ref name="time-life"/> The shaggy coat has grooved hair that is host to symbiotic [[green algae]] which camouflage the animal in the trees and provide it nutrients. The algae also nourish [[sloth moth]]s, some species of which exist solely on sloths.<ref name="gizmodo">{{cite web |last1=Bennington-Castro |first1=Joseph |title=The Strange Symbiosis Between Sloths and Moths |url=https://io9.gizmodo.com/the-strange-symbiosis-between-sloths-and-moths-1506856445 |website=Gizmodo |date=23 January 2014 |access-date=1 December 2017 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201234154/https://io9.gizmodo.com/the-strange-symbiosis-between-sloths-and-moths-1506856445 |url-status=live }}</ref>

==Taxonomy and evolution==
{{see also|List of pilosans}}
Sloths belong to the superorder [[Xenarthra]], a group of [[Placentalia|placental]] [[mammal]]s believed to have evolved in the continent of South America around 60 million years ago.<ref>{{Cite journal|last1=O'Leary|first1=Maureen A.|last2=Bloch|first2=Jonathan I.|last3=Flynn|first3=John J.|last4=Gaudin|first4=Timothy J.|last5=Giallombardo|first5=Andres|last6=Giannini|first6=Norberto P.|last7=Goldberg|first7=Suzann L.|last8=Kraatz|first8=Brian P.|last9=Luo|first9=Zhe-Xi|date=2013-02-08|title=The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals|journal=Science|language=en|volume=339|issue=6120|pages=662–667|doi=10.1126/science.1229237|issn=0036-8075|pmid=23393258|bibcode=2013Sci...339..662O|s2cid=206544776|hdl=11336/7302|hdl-access=free}}</ref> One study found that xenarthrans broke off from other placental mammals around 100 million years ago.<ref>{{Cite journal|last1=Svartman|first1=Marta|last2=Stone|first2=Gary|last3=Stanyon|first3=Roscoe|date=2006-07-21|title=The Ancestral Eutherian Karyotype Is Present in Xenarthra|journal=PLOS Genetics|volume=2|issue=7|pages=e109|doi=10.1371/journal.pgen.0020109|issn=1553-7404|pmc=1513266|pmid=16848642 |doi-access=free }}</ref> [[Anteater]]s and [[armadillo]]s are also included among Xenarthra. The earliest xenarthrans were arboreal [[herbivore]]s with sturdy [[vertebral column]]s, fused [[pelvis]]es, stubby teeth, and small brains. Sloths are in the taxonomic suborder [[Folivora]]<ref name="Delsuc2001">{{Cite journal|last1=Delsuc|first1=Frédéric|last2=Catzeflis|first2=François M.|last3=Stanhope|first3=Michael J.|last4=Douzery|first4=Emmanuel J. P.|date=2001-08-07|title=The evolution of armadillos, anteaters and sloths depicted by nuclear and mitochondrial phylogenies: implications for the status of the enigmatic fossil ''Eurotamandua''|journal=Proceedings of the Royal Society of London B: Biological Sciences|language=en|volume=268|issue=1476|pages=1605–1615|doi=10.1098/rspb.2001.1702|issn=0962-8452|pmid=11487408|pmc=1088784}}</ref> of the order [[Pilosa]]. These names are from the Latin 'leaf eater' and 'hairy', respectively. Pilosa is one of the smallest of the orders of the [[mammal]] class; its only other suborder contains the anteaters.

The Folivora are divided into at least eight families, only two of which have living species; the remainder are entirely extinct ([[Extinction|†]]):<ref name="Presslee2019" />

*†[[Megalocnidae]]: the [[Pilosans of the Caribbean|Greater Antilles sloths]], a [[Basal (phylogenetics)|basal]] group that arose about 32 million years ago and became extinct about 5,000 years ago.<ref name="Presslee2019" />
*Superfamily '''Megatherioidea'''
** Bradypodidae, the [[three-toed sloth]]s, contains four extant species:
*** The [[Brown-throated sloth|brown-throated three-toed sloth (''Bradypus variegatus'')]] is the most common of the extant species of sloth, which inhabits the [[Neotropical realm]]<ref name=msw3/><ref name="gardner">{{Cite book
  | first = Alfred L.
  | last = Gardner
  | editor-last = Gardner
  | editor-first = Alfred L.
  | contribution = Suborder Folivora
  | contribution-url = http://google.com/books?id=dbU3d7EUCm8C&pg=PA161
  | title = Mammals of South America, Volume 1: Marsupials, Xenarthrans, Shrews, and Bats
  | year = 2007
  | pages = 157–168 (p. 161)
  | place = Chicago
  | publisher = [[University of Chicago Press]]
  | url = http://www.press.uchicago.edu/presssite/metadata.epl?isbn=9780226282404
  | isbn = 978-0-226-28240-4
  | access-date = 29 November 2017
  | archive-date = 27 November 2018
  | archive-url = https://web.archive.org/web/20181127233650/http://vertebrates.si.edu/mammals/mammals_staff_pages/gardner_alfred.cfm
  | url-status = dead
  }}</ref> in the forests of South and Central America.
*** The [[Pale-throated sloth|pale-throated three-toed sloth (''Bradypus tridactylus'')]], which inhabits tropical rainforests in northern South America. It is similar in appearance to, and often confused with, the brown-throated three-toed sloth, which has a much wider distribution. Genetic evidence indicates the two species diverged around six million years ago.<ref name="Moraes-Barros2011">{{cite journal | author = Moraes-Barros, M.C.| year = 2011 | title = Morphology, molecular phylogeny, and taxonomic inconsistencies in the study of Bradypus sloths (Pilosa: Bradypodidae) | journal = Journal of Mammalogy | volume = 92 | issue = 1 | pages = 86–100 | doi = 10.1644/10-MAMM-A-086.1|display-authors=etal| doi-access = free }}</ref>
*** The [[Maned sloth|maned three-toed sloth (''Bradypus torquatus'')]], now found only in the [[Atlantic Forest]] of southeastern Brazil.
*** The critically endangered [[pygmy three-toed sloth]] (''Bradypus pygmaeus'') which is [[endemic]] to the small island of [[Isla Escudo de Veraguas]] off the coast of [[Panama]].
**†[[Megalonychidae]]: ground sloths that existed for about 35 million years and went extinct about 11,000 years ago. This group was formerly thought to include both the two-toed sloths and the extinct Greater Antilles sloths.
**†[[Megatheriidae]]: ground sloths that existed for about 23 million years and went extinct about 11,000 years ago; this family included the largest sloths.
**†[[Nothrotheriidae]]: ground sloths that lived from approximately 11.6 million to 11,000 years ago. As well as ground sloths, this family included ''[[Thalassocnus]]'', a genus of either semiaquatic or fully aquatic sloths.
*Superfamily '''Mylodontoidea'''
** Choloepodidae, the [[two-toed sloth]]s, contains two extant species:
*** [[Linnaeus's two-toed sloth]] (''Choloepus didactylus'') found in [[Venezuela]], [[the Guianas]], [[Colombia]], [[Ecuador]], [[Peru]], and [[Brazil]] north of the [[Amazon River]].
*** [[Hoffmann's two-toed sloth]] (''Choloepus hoffmanni'') which inhabits tropical forests. It has two separate ranges, split by the [[Andes]]. One population is found from eastern [[Honduras]]<ref name="iucn">{{cite iucn | author = Plese, T. | author2 = Chiarello, A. | title = ''Choloepus hoffmanni'' | volume = 2014 | page = e.T4778A47439751 | year = 2014 | doi = 10.2305/IUCN.UK.2014-1.RLTS.T4778A47439751.en }}</ref> in the north to western Ecuador in the south, and the other in eastern Peru, western Brazil, and northern [[Bolivia]].<ref name="Hayssen2011">{{cite journal | author = Hayssen, V. | year = 2011 | title = ''Choloepus hoffmanni'' (Pilosa: Megalonychidae) | journal = Mammalian Species | volume = 43 | issue = 1 | pages = 37–55 | doi = 10.1644/873.1| doi-access = free }}</ref>
**†[[Mylodontidae]]: ground sloths that existed for about 23 million years and went extinct about 11,000 years ago.
**†[[Scelidotheriidae]]: collagen sequence data indicates this group is more distant from ''[[Mylodon]]'' than ''[[Choloepus]]'' is, so it has been elevated back to full family status.<ref name="Presslee2019" />

[[File:Megatherium americanum Skeleton NHM.JPG|thumb|''[[Megatherium|Megatherium americanum]]'' ([[Megatheriidae]], [[Natural History Museum, London|London]])]]

===Evolution===
[[File:Nothrotheriops shastensis La Brea.jpg|thumb|''[[Nothrotheriops|Nothrotheriops shastensis]]'' ([[Nothrotheriidae]], [[La Brea Tar Pits Museum|La Brea]])]]
The common ancestor of the two existing sloth genera dates to about 28 million years ago,<ref name="Presslee2019" /> with similarities between the two- and three- toed sloths an example of [[convergent evolution]] to an [[arboreal]] lifestyle, "one of the most striking examples of convergent evolution known among mammals".<ref name="gaudin2004">{{Cite journal|last=Gaudin|first= T.J.|date=2004-02-01|title=Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence|journal=Zoological Journal of the Linnean Society|volume= 140|issue= 2|pages= 255–305|doi= 10.1111/j.1096-3642.2003.00100.x|issn =0024-4082|doi-access=free}}</ref> The ancient Xenarthra included a significantly greater variety of species, with a wider distribution, than those of today. Ancient sloths were mostly terrestrial, and some reached sizes that rival those of elephants, as was the case for ''[[Megatherium]]''.<ref name="time-life">{{cite book|title=The Land and Wildlife of South America|url=https://archive.org/details/landwildlifeof00bate|url-access=registration|date=1964|publisher=Time Inc.|pages=[https://archive.org/details/landwildlifeof00bate/page/15 15], 54}}</ref>
[[File:Megalonyx wheatleyi skeleton & restoration.jpg|thumb|''[[Megalonyx|Megalonyx wheatleyi]]'' ([[Megalonychidae]]) [[fossil]] ([[American Museum of Natural History|AMNH]]) and restoration]]
[[File:San Diego Paramylodon.jpg|thumb|''[[Paramylodon|Paramylodon harlani]]'' ([[Mylodontidae]], [[San Diego Natural History Museum|San Diego]])]]
Sloths arose in South America during a long period of isolation and eventually spread to a number of the Caribbean islands as well as North America. It is thought that swimming led to [[oceanic dispersal]] of [[Pilosans of the Caribbean|pilosans]] to the [[Greater Antilles]] by the [[Oligocene]], and that the megalonychid ''[[Pliometanastes]]'' and the [[Mylodontidae|mylodontid]] ''[[Thinobadistes]]'' were able to colonise North America about 9 million years ago, well before the formation of the [[Isthmus of Panama]]. The latter development, about 3 million years ago, allowed megatheriids and nothrotheriids to also invade North America as part of the [[Great American Interchange]]. Additionally, the [[Nothrotheriidae|nothrotheriid]] ''[[Thalassocnus]]'' of the west coast of South America became adapted to a [[semiaquatic]] and, eventually, perhaps fully aquatic [[Marine mammal|marine]] lifestyle.<ref name="Muizen2004">{{cite journal|last=Muizon|first=C. de|author2=McDonald, H. G.|author3=Salas, R.|author4=Urbina, M.|date=June 2004|title=The evolution of feeding adaptations of the aquatic sloth ''Thalassocnus''|journal=Journal of Vertebrate Paleontology|volume=24|issue=2|pages=398–410|doi=10.1671/2429b|jstor=4524727|bibcode=2004JVPal..24..398D |s2cid=83859607}}</ref> In [[Peru]] and [[Chile]], ''Thalassocnus'' entered the coastal habitat beginning in the late [[Miocene]]. They presumably waded and paddled in the water for short period, but over a span of 4 million years, they eventually evolved into swimming creatures, becoming specialist bottom feeders of [[seagrass]]es, similar to the extant [[sirenia]]ns.<ref name="Amsonetal2014">{{cite journal|last1=Amson|first1=E.|last2=Muizon|first2=C. de|last3=Laurin|first3=M.|last4=Argot|first4=C.|last5=Buffrénil|first5=V. de|date=2014|title=Gradual adaptation of bone structure to aquatic lifestyle in extinct sloths from Peru|journal=Proceedings of the Royal Society B: Biological Sciences|volume= 281|issue= 1782|page= 20140192|doi= 10.1098/rspb.2014.0192|pmc= 3973278|pmid= 24621950}}</ref>

Both types of extant tree sloth tend to occupy the same forests; in most areas, a particular species of the somewhat smaller and generally slower-moving [[three-toed sloth]] (''Bradypus'') and a single species of the two-toed type will jointly predominate. Based on morphological comparisons, it was thought the two-toed sloths nested phylogenetically within one of the divisions of the extinct [[Megalocnidae|Greater Antilles sloths]].<ref name="White">{{Cite book
 |last1         = White
 |first1        = J.L.
 |last2         = MacPhee
 |first2        = R.D.E.
 |title         = Biogeography of the West Indies: Patterns and Perspectives
 |editor-last   = Woods
 |editor-first  = C.A.
 |editor2-last  = Sergile
 |editor2-first = F.E.
 |publisher     = [[CRC Press]]
 |year          = 2001
 |chapter       = The sloths of the West Indies: a systematic and phylogenetic review
 |chapter-url   = https://books.google.com/books?id=f33LBQAAQBAJ&pg=PA201
 |pages         = 201–235
 |url           = https://books.google.com/books?id=f33LBQAAQBAJ
 |location      = Boca Raton, London, New York, and Washington, D.C.
 |doi           = 10.1201/9781420039481-14
 |isbn          = 978-0-8493-2001-9
 |access-date   = 9 June 2020
 |archive-date  = 24 May 2021
 |archive-url   = https://web.archive.org/web/20210524175141/https://books.google.com/books?id=f33LBQAAQBAJ
 |url-status    = live
}}</ref> Though data has been collected on over 33 different species of sloths by analyzing bone structures, many of the relationships between clades on a phylogenetic tree were unclear.<ref name="gaudin2004"/> Much of the morphological evidence collected to support the hypothesis of diphyly has been based on the structure of the inner ear.<ref name="Pant2014">{{cite journal|doi=10.1186/s12862-014-0184-1|pmid=25319928|pmc=4243956|title=Complex body size trends in the evolution of sloths (Xenarthra: Pilosa)|journal=BMC Evolutionary Biology|volume=14|page=184|year=2014|last1=Raj Pant|first1=Sara|last2=Goswami|first2=Anjali|last3=Finarelli|first3=John A |issue=1 |bibcode=2014BMCEE..14..184R |doi-access=free }}</ref>

Recently obtained molecular data from [[collagen]]<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 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.|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|access-date= 18 September 2020|archive-date= 12 September 2020|archive-url= https://web.archive.org/web/20200912204649/http://eprints.whiterose.ac.uk/147061/1/5426_3_merged_1554730549.pdf|url-status= live}}</ref> and [[mitochondrial DNA]] sequences<ref name="Delsuc2019">{{cite journal|last1= Delsuc|first1= F.|last2= Kuch|first2= M.|last3= Gibb|first3= G. C.|last4= Karpinski|first4= E.|last5= Hackenberger|first5= D.|last6= Szpak|first6= P.|last7= Martínez|first7= J. G.|last8= Mead|first8= J. I.|last9= McDonald|first9= H. G.|last10= MacPhee|first10= R.D.E.|last11= Billet|first11= G.|last12= Hautier|first12= L.|last13= Poinar|first13= H. N.|title= Ancient Mitogenomes Reveal the Evolutionary History and Biogeography of Sloths|journal= Current Biology|volume= 29|issue= 12|pages= 2031–2042.e6|year= 2019|url= https://www.researchgate.net/publication/333647272|doi= 10.1016/j.cub.2019.05.043|pmid= 31178321|doi-access= free|bibcode= 2019CBio...29E2031D|access-date= 11 June 2020|archive-date= 23 March 2022|archive-url= https://web.archive.org/web/20220323230645/https://www.researchgate.net/publication/333647272_Ancient_Mitogenomes_Reveal_the_Evolutionary_History_and_Biogeography_of_Sloths|url-status= live|hdl= 11336/136908|hdl-access= free}}</ref> fall in line with the diphyly (convergent evolution) hypothesis but have overturned some of the other conclusions obtained from morphology. These investigations consistently place two-toed sloths close to [[mylodontid]]s and three-toed sloths within Megatherioidea, close to ''[[Megalonyx]]'', [[megatheriid]]s and [[nothrotheriid]]s. They make the previously recognized family [[Megalonychidae]] [[polyphyletic]], with both two-toed sloths and Greater Antilles sloths being moved away from ''Megalonyx''. Greater Antilles sloths are now placed in a separate, [[Basal (phylogenetics)|basal]] branch of the sloth evolutionary tree.<ref name="Presslee2019" /><ref name="Delsuc2019" />

===Phylogeny===
The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data.<ref name="Presslee2019" />

{{clade | style = font-size: 100%;line-height:100%
| label1 ='''Folivora'''
|1={{clade
  |1=[[Megalocnidae]] (Greater Antilles sloths)
  |2={{clade
    |1={{clade
      |1={{clade
        |1=[[Scelidotheriidae]]
        |2={{clade
          |1=[[Mylodontidae]]
          |2=[[Choloepodidae]] (two-toed sloths)
        }}
      }}
      |2={{clade
        |1={{clade
          |1=[[Megalonychidae]]
          |2=[[Bradypodidae]] (three-toed sloths)
        }}
        |2={{clade
          |1=[[Nothrotheriidae]]
          |2=[[Megatheriidae]]
        }}
      }}
      |grouplabelstyle1=vertical-align:left;
      |grouplabel1={{clade label|'''Mylodontoidea'''|color=blue|width=7.5em}}
      |bar1=blue
      |grouplabel2={{clade label|'''Megatherioidea'''|color=red|width=8em}}
      |bar2=red
    }}
  }}
}}
}}

===Extinctions===
The marine sloths of South America's Pacific coast became extinct at the end of the Pliocene following the closing of the [[Central American Seaway]]; the closing caused a cooling trend in the coastal waters which killed off much of the area's [[seagrass]] (and which would have also made thermoregulation difficult for the sloths, with their slow metabolism).<ref name="Amson2015">{{Cite journal|last1= Amson|first1= E.|last2= Argot|first2= C.|last3= McDonald|first3=H. G.|last4=de Muizon|first4= C.|year= 2015|title= Osteology and functional morphology of the axial postcranium of the marine sloth ''Thalassocnus'' (Mammalia, Tardigrada) with paleobiological implications|journal= Journal of Mammalian Evolution|volume= 22|issue= 4|pages= 473–518|doi= 10.1007/s10914-014-9280-7|s2cid= 16700349}}</ref>

Ground sloths disappeared from both North and South America shortly after the appearance of humans about 11,000 years ago. Evidence suggests human hunting contributed to the extinction of the American [[megafauna]]. Ground sloth remains found in both North and South America indicate that they were killed, cooked, and eaten by humans.<ref name="time-life"/> [[Climate variability and change|Climate change]] that came with the end of the last [[ice age]] may have also played a role, although previous similar glacial retreats were not associated with similar extinction rates.

''[[Megalocnus]]'' and some other Caribbean sloths survived until about 5,000 years ago, long after ground sloths had died out on the mainland, but then went extinct when humans finally colonized the Greater Antilles.<ref name="Steadman">{{cite journal|last=Steadman|first=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.|date=2005-08-16|title=Asynchronous extinction of late Quaternary sloths on continents and islands|journal=[[Proceedings of the National Academy of Sciences|Proc. Natl. Acad. Sci. USA]]|volume=102|issue=33|pages=11763–11768|doi=10.1073/pnas.0502777102|pmc=1187974|pmid=16085711|bibcode=2005PNAS..10211763S|author1-link=David Steadman|author2-link=Paul Schultz Martin|doi-access=free}}</ref>

==Biology==
[[File:MC Drei-Finger-Faultier.jpg|thumb|left|Feeding [[Brown-throated sloth|brown-throated three-toed sloth]] (''Bradypus variegatus''), [[Cahuita National Park]], [[Costa Rica]]]]

=== Morphology and anatomy ===
[[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)]]
Sloths can be {{cvt|60|to|80|cm}} long and, depending on the species, weigh from {{cvt|3.6|to|7.7|kg}}. Two-toed sloths are slightly larger than three-toed sloths.<ref>{{cite web|title=Sloth|url=https://kids.nationalgeographic.com/animals/mammals/facts/sloth|website=National Geographic|date=March 2014|access-date=1 December 2017|archive-date=11 April 2019|archive-url=https://web.archive.org/web/20190411125624/https://kids.nationalgeographic.com/animals/sloth/#sloth-beach-upside-down.jpg|url-status=live}}</ref> Sloths have long limbs and rounded heads with tiny ears. Three-toed sloths also have stubby tails about {{convert|5|to|6|cm|abbr=on}} long.

Sloths are unusual among [[mammal]]s in not having seven [[cervical vertebrae]]. Two-toed sloths have five to seven, while three-toed sloths have eight or nine. The other mammals not having seven are the [[manatee]]s, with six.<ref>{{cite web |title=Sticking their necks out for evolution: Why sloths and manatees have unusually long (or short) necks |url=https://www.sciencedaily.com/releases/2011/05/110505212314.htm |website=ScienceDaily |access-date=26 April 2019 |archive-date=26 April 2019 |archive-url=https://web.archive.org/web/20190426223708/https://www.sciencedaily.com/releases/2011/05/110505212314.htm |url-status=live }}</ref>

=== Physiology ===
Sloths have colour vision but have poor visual acuity. They also have poor hearing. Thus, they rely on their sense of smell and touch to find food.<ref name="bri">{{cite web|title=Sloth|url=https://www.britannica.com/animal/sloth|website=Encyclopedia Britannica|access-date=1 December 2017|archive-date=19 May 2017|archive-url=https://web.archive.org/web/20170519141514/https://www.britannica.com/animal/sloth|url-status=live}}</ref>

Sloths have very low [[Metabolism|metabolic]] rates (less than half of that expected for a mammal of their size), and low body temperatures: {{cvt|30|to|34|C}} when active, and still lower when resting. Sloths are [[heterothermic]], meaning their body temperature may vary according to the environment, normally ranging from {{cvt|25|to|35|C}}, but able to drop to as low as {{cvt|20|C}}, inducing [[torpor]].<ref name="bri" />

[[Brown-throated sloth|Brown-throathed]] and [[Hoffmann's two-toed sloth|Hoffman's two-toed]] sloths use their forelimbs as their principal means of propulsion and their skeletal muscle have very high proportions of oxidative [[Skeletal muscle|slow twitch]] (Type I) muscle fibers, with high activity of the [[Anaerobic respiration|anaerobic]] enzyme [[Creatine kinase|CK]] compared to their other metabolic enzymes despite this. CK activity is low compared with other animals. Their muscle fibers proportion would be an adaptation to consume energy more slowly and their principally anaerobic muscle metabolism would be to use energy production sources faster and cheaper, such as ATP production by CK pathway. This would be a product of their lower [[field metabolic rate]] than other nonhibernating mammals as well suspensory lifestyle and this also would to explain their slow speed of movement.<ref>{{Cite journal |last1=Spainhower |first1=K. B. |last2=Cliffe |first2=R. N. |last3=Metz |first3=A. K. |last4=Barkett |first4=E. M. |last5=Kiraly |first5=P. M. |last6=Thomas |first6=D. R. |last7=Kennedy |first7=S. J. |last8=Avey-Arroyo |first8=J. A. |last9=Butcher |first9=M. T. |date=2018 |title=Cheap labor: myosin fiber type expression and enzyme activity in the forelimb musculature of sloths (Pilosa: Xenarthra) |url=https://journals.physiology.org/doi/full/10.1152/japplphysiol.01118.2017 |journal=Journal of Applied Physiology |volume=125 |issue=3 |pages=799–811 |doi=10.1152/japplphysiol.01118.2017 |pmid=29722617 |issn=8750-7587}}</ref> Forelimb muscle mass makes up only 5.1 % of total body weight in the brown-throated sloth.<ref>{{Cite journal |last1=Olson |first1=R. A. |last2=Glenn |first2=Z. D. |last3=Cliffe |first3=R. N. |last4=Butcher |first4=M. T. |date=2018 |title=Architectural Properties of Sloth Forelimb Muscles (Pilosa: Bradypodidae) |url=https://www.academia.edu/57579185 |journal=Journal of Mammalian Evolution |language=en |volume=25 |issue=4 |pages=573–588 |doi=10.1007/s10914-017-9411-z |issn=1573-7055}}</ref>

The outer hairs of sloth fur grow in a direction opposite from that of other mammals. In most mammals, hairs grow toward the [[Appendicular skeleton|extremities]], but because sloths spend so much time with their limbs above their bodies, their hairs grow away from the extremities to provide protection from the elements while they hang upside down. In most conditions, the fur hosts symbiotic algae, which provide [[camouflage]]<ref>{{Cite journal|last1=Suutari|first1=Milla|last2=Majaneva|first2=Markus|last3=Fewer|first3=David P.|last4=Voirin|first4=Bryson|last5=Aiello|first5=Annette|author-link5=Annette Aiello|last6=Friedl|first6=Thomas|last7=Chiarello|first7=Adriano G.|last8=Blomster|first8=Jaanika|date=2010-01-01|title=Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with Trichophilus welckeri(Chlorophyta, Ulvophyceae)|journal=BMC Evolutionary Biology|volume=10|issue=1 |page=86|doi=10.1186/1471-2148-10-86|issn=1471-2148|pmc=2858742|pmid=20353556 |bibcode=2010BMCEE..10...86S |doi-access=free }}</ref> from predatory [[jaguar]]s, [[ocelot]]s,<ref>{{Cite journal|last1=Moreno|first1=Ricardo S.|last2=Kays|first2=Roland W.|last3=Samudio|first3=Rafael|date=2006-08-24|title=Competitive Release in Diets of Ocelot (Leopardus pardalis) and Puma (Puma concolor) after Jaguar (Panthera onca) Decline|journal=Journal of Mammalogy|volume=87|issue=4|pages=808–816|doi=10.1644/05-MAMM-A-360R2.1|s2cid=37859321 |issn=0022-2372|doi-access=}}</ref> and [[harpy eagle]]s.<ref>{{Cite journal|last1=Aguiar-Silva|first1=F. Helena|last2=Sanaiotti|first2=Tânia M.|last3=Luz|first3=Benjamim B.|date=2014-03-01|title=Food Habits of the Harpy Eagle, a Top Predator from the Amazonian Rainforest Canopy|journal=Journal of Raptor Research|volume=48|issue=1|pages=24–35|doi=10.3356/JRR-13-00017.1|s2cid=86270583|issn=0892-1016|doi-access=free}}</ref> Because of the algae, sloth fur is a small ecosystem of its own, hosting many species of [[Commensalism|commensal]] and [[Parasitism|parasitic]] [[arthropod]]s.<ref name="Sloth arthropod biology"/> There are a large number of [[arthropods associated with sloths]]. These include biting and blood-sucking flies such as [[mosquito]]es and [[Sandfly|sandflies]], [[Triatominae|triatomine bugs]], [[Louse|lice]], [[tick]]s and [[mite]]s. Sloths have a highly specific community of commensal [[beetle]]s, mites and [[moth]]s.<ref name="Sloth arthropod biology">{{cite journal|last1=Gilmore|first1=D. P.|last2=Da Costa|first2=C. P.|last3=Duarte|first3=D. P. F.|year=2001|title=Sloth biology: an update on their physiological ecology, behavior and role as vectors of arthropods and arboviruses|url=http://www.scielo.br/pdf/bjmbr/v34n1/3877m.pdf|journal=Brazilian Journal of Medical and Biological Research|volume=34|issue=1|pages=9–25|doi=10.1590/S0100-879X2001000100002|issn=1678-4510|pmid=11151024|doi-access=free|access-date=1 December 2017|archive-date=6 November 2020|archive-url=https://web.archive.org/web/20201106160418/http://www.scielo.br/pdf/bjmbr/v34n1/3877m.pdf|url-status=live}}</ref> The species of sloths recorded to host arthropods include<ref name="Sloth arthropod biology" /> the pale-throated three-toed sloth, the brown-throated three-toed sloth, and Linnaeus's two-toed sloth. Sloths benefit from their relationship with moths because the moths are responsible for fertilizing algae on the sloth, which provides them with nutrients.<ref>{{cite web|url=http://phenomena.nationalgeographic.com/2014/01/21/can-moths-explain-why-sloths-poo-on-the-ground/|title=Can Moths Explain Why Sloths Poo on the Ground?|author=Ed Yong|author-link=Ed Yong|work=Phenomena|date=2014-01-21|access-date=23 January 2014|archive-date=29 May 2018|archive-url=https://web.archive.org/web/20180529070736/http://phenomena.nationalgeographic.com/2014/01/21/can-moths-explain-why-sloths-poo-on-the-ground/|url-status=dead}}</ref>

=== Activity ===
Sloth limbs are adapted for hanging and grasping, not for supporting their weight. Muscle mass makes up only 25 to 30 percent of their total body weight. Most other mammals have a muscle mass that makes up 40 to 45 percent of their total body weight.<ref>{{cite web|url=http://natureinstitute.org/nature/sloth.htm|title=What Does It Mean to Be a Sloth?|website=natureinstitute.org|access-date=2017-06-29|archive-date=15 June 2019|archive-url=https://web.archive.org/web/20190615043130/http://natureinstitute.org/nature/sloth.htm|url-status=live}}</ref> Their specialised hands and feet have long, curved claws to allow them to hang upside down from branches without effort,<ref>{{Cite journal|last=Mendel|first=Frank C.|date=1985-01-01|title=Use of Hands and Feet of Three-Toed Sloths (Bradypus variegatus) during Climbing and Terrestrial Locomotion|journal=Journal of Mammalogy|volume=66|issue=2|pages=359–366|doi=10.2307/1381249|jstor=1381249}}</ref> and are used to drag themselves along the ground, since they cannot walk. On three-toed sloths, the arms are 50 percent longer than the legs.<ref name="bri" />

Sloths move only when necessary and even then, very slowly. They usually move at an average speed of {{cvt|4|m}} per minute but can move at a marginally higher speed of {{cvt|4.5|m}} per minute if they are in immediate danger from a predator. While they sometimes sit on top of branches, they usually eat, sleep, and even give birth hanging from branches. They sometimes remain hanging from branches even after death. On the ground, the maximum speed of sloths is {{cvt|3|m}} per minute. Two-toed sloths are generally better able than three-toed sloths to disperse between clumps of trees on the ground.<ref name="Peery2018">{{Cite journal|last1=Garcés-Restrepo|first1= M.F.|last2= Pauli|first2= J.N.|last3= Peery|first3= M.Z.|date= 2018|title= Natal dispersal of tree sloths in a human-dominated landscape: Implications for tropical biodiversity conservation|journal= Journal of Applied Ecology|volume= 55|issue= 5|pages= 2253–2262|doi= 10.1111/1365-2664.13138|bibcode= 2018JApEc..55.2253G|doi-access= free}}</ref>

Sloths are surprisingly strong swimmers and can reach speeds of {{cvt|13.5|m}} per minute.<ref>{{Cite journal|last= Goffart|first= M.|date= 1971|title= Function and Form in the sloth|journal=International Series of Monographs in Pure and Applied Biology|volume=34|pages=94–95}}</ref> They use their long arms to paddle through the water and can cross rivers and swim between islands.<ref>{{Citation|last=BBC|title=Swimming sloth - Planet Earth II: Islands Preview - BBC One|date= 2016-11-04|url= https://www.youtube.com/watch?v=ctutKTrf_NY| archive-url=https://ghostarchive.org/varchive/youtube/20211030/ctutKTrf_NY| archive-date=2021-10-30|access-date=2017-04-17}}{{cbignore}}</ref> Sloths can reduce their already slow metabolism even further and slow their heart rate to less than a third of normal, allowing them to hold their breath underwater for up to 40 minutes.<ref>{{Cite journal|last=Britton|first=S. W.|date=1941-01-01|title=Form and Function in the Sloth|journal=The Quarterly Review of Biology|volume=16|issue=1|pages=13–34|doi=10.1086/394620|jstor=2808832|s2cid=85162387}}</ref>

Wild brown-throated three-toed sloths sleep on average 9.6 hours a day.<ref>{{cite news|url=http://news.bbc.co.uk/2/hi/science/nature/7396356.stm|title=Article "Sloth's Lazy Image 'A Myth'"|last=Briggs|first=Helen|date=2008-05-13|access-date=2010-05-21|publisher=BBC News|archive-date=1 January 2021|archive-url=https://web.archive.org/web/20210101110716/http://news.bbc.co.uk/2/hi/science/nature/7396356.stm|url-status=live}}</ref> Two-toed sloths are [[nocturnal]].<ref name="Eisenberg2000">{{Cite book |url=https://books.google.com/books?id=p2MDAzCeQQoC&pg=PA94 |title=Mammals of the Neotropics, Volume 3: The Central Neotropics: Ecuador, Peru, Bolivia, Brazil |last=Eisenberg |first=John F. |author2=Redford, Kent H. |date=15 May 2000 |publisher=[[University of Chicago Press]] |isbn=978-0-226-19542-1 |pages=624 |oclc=493329394 |access-date=25 September 2016 |archive-date=19 September 2020 |archive-url=https://web.archive.org/web/20200919145623/https://books.google.com/books?id=p2MDAzCeQQoC&pg=PA94 |url-status=live}}</ref>{{rp|94–95, 97}} Three-toed sloths are mostly nocturnal but can be active in the day. They spend 90 per cent of their time motionless.<ref name="bri" />

===Behavior===
Sloths are solitary animals that rarely interact with one another except during breeding season,<ref name=livesci>{{cite web |title=Sloths: The World's Slowest Mammals |author=Alina Bradford |website=Live Science |date=26 Nov 2018 |url=https://www.livescience.com/27612-sloths.html |access-date=22 November 2020 |archive-date=4 December 2020 |archive-url=https://web.archive.org/web/20201204193927/https://www.livescience.com/27612-sloths.html |url-status=live }}</ref> though female sloths do sometimes congregate, more so than do males.<ref>{{cite web |title=Sloth |website=Animal Corner |url=https://animalcorner.org/animals/sloth/ |access-date=22 November 2020 |archive-date=8 November 2020 |archive-url=https://web.archive.org/web/20201108113808/https://animalcorner.org/animals/sloth/ |url-status=live }}</ref>

Sloths descend about once every eight days to defecate on the ground. The reason and mechanism behind this behavior have long been debated among scientists. There are at least five hypotheses:
# To fertilize trees when feces are deposited at the base of the tree<ref>{{cite journal |last1=Montgomery |first1=G. G. |last2=Sunquist |first2=M. E. |year=1975 |title=Impact of Sloths on Neotropical Forest Energy Flow and Nutrient Cycling |journal=Ecological Studies |pages=69–98 |doi=10.1007/978-3-642-88533-4_7}}</ref>
# To cover feces and avoid predation<ref>{{cite journal |last1=Bailey |first1=T. N. |year=1974 |title=Social organization in a bobcat population |journal=The Journal of Wildlife Management |volume=38 |issue=3 |pages=435-446 |doi=10.2307/3800874 |jstor=3800874}}</ref><ref>{{cite journal |last1=Liberg |first1=O. |year=1980 |title=Spacing patterns in a population of rural free roaming domestic cats |journal=Oikos |volume=32 |issue=3 |pages=336-349 |doi=10.2307/3544649 |jstor=3544649}}</ref><ref name=":0">{{cite journal |last1=Pauli |first1=J. N. |last2=Mendoza |first2=J. E. |last3=Steffan |first3=S. A. |last4=Carey |first4=C. C. |last5=Weimer |first5=P. J. |last6=Peery |first6=M. Z. |year=2014 |title=A syndrome of mutualism reinforces the lifestyle of a sloth |journal=Proceedings of the Royal Society B: Biological Sciences |volume=281 |issue=1778 |page=20133006 |doi=10.1098/rspb.2013.3006}}</ref>
# To serve as chemical communication between individuals<ref>{{cite book |last1=Chiarello |first1=A. G. |year=2008 |chapter=Sloth ecology: an overview of field studies |title=The biology of the Xenarthra |pages=269-280 |publisher=University Press of Florida |editor1-last=Vizcaíno |editor1-first=S. F. |editor2-last=Loughry |editor2-first=W. J. |chapter-url=https://www.researchgate.net/publication/313343711}}</ref>
# To pick up trace nutrients in their claws, that are then ingested,<ref name=":1">{{cite book |last1=Voirin |first1=B. |last2=Kays |first2=R. |last3=Wikelski |first3=M. |last4=Lowman |first4=M. |year=2013 |chapter=Why Do Sloths Poop on the Ground |editor1-first=M. |editor1-last=Lowman |editor2-first=S. |editor2-last=Devy |editor3-first=T. |editor3-last=Ganesh |title=Treetops at Risk |pages=195-199 |publisher=Springer |location=New York, NY |doi=10.1007/978-1-4614-7161-5_19}}</ref> and
# To favor a mutualistic relationship with populations of fur moths.<ref name=":0" /><ref name=":1" />

More recently, a new hypothesis has emerged, which presents evidence against the previous ones and proposes that all current sloths are descendants from species that defecated on the ground, and there simply has not been enough selective pressure to abandon this behavior, since cases of predation during defecation are actually very rare.<ref>{{cite journal |last1=Monge Nájera |first1=J. |year=2021 |title=Why sloths defecate on the ground: rejection of the mutualistic model |journal=UNED Research Journal |volume=13 |issue=1 |page=e3438 |doi=10.22458/urj.v13i1.3438|doi-access=free }}</ref>

===Diet===
[[File:Two-toed sloth Costa Rica - cropped.jpg|thumb|right|[[Hoffman's two-toed sloth]] (''Choloepus hoffmanni'') feeding in [[Manuel Antonio National Park]] in [[Costa Rica]]]]Baby sloths learn what to eat by licking the lips of their mother.<ref>{{Cite news|url=https://www.bbc.com/news/magazine-26734289|title=The woman who got 'slothified'|last=Venema|first=Vibeke|date=2014-04-04|work=BBC News|access-date=2017-12-01|language=en-GB|archive-date=6 March 2021|archive-url=https://web.archive.org/web/20210306065530/https://www.bbc.com/news/magazine-26734289|url-status=live}}</ref> All sloths eat the leaves of ''[[Cecropia]]''.

Two-toed sloths are [[omnivorous]], with a diverse diet of [[insects]], [[carrion]], [[fruits]], [[leaves]] and small [[lizards]], ranging over up to {{Convert|140|ha||abbr=}}. Three-toed sloths, on the other hand, are almost entirely [[herbivorous]] (plant eaters), with a limited diet of leaves from only a few trees,<ref name=livesci/> and no other mammal digests its food as slowly.

They have made adaptations to [[arboreal]] browsing. Leaves, their main food source, provide very little energy or nutrients, and do not digest easily, so sloths have large, slow-acting, multi-chambered [[stomachs]] in which [[symbiotic bacteria]] break down the tough leaves.<ref name=livesci /> As much as two-thirds of a well-fed sloth's body weight consists of the contents of its stomach, and the [[digestion|digestive process]] can take a month or more to complete.

Three-toed sloths go to the ground to urinate and defecate about once a week, digging a hole and covering it afterwards. They go to the same spot each time and are vulnerable to predation while doing so. Considering the large energy expenditure and dangers involved in the journey to the ground, this behaviour has been described as a mystery.<ref>{{cite web |url=https://www.youtube.com/watch/ndMKTnSRsKM |title=The 'Busy' Life of the Sloth &#124; BBC Earth |publisher=YouTube |date=2009-05-18 |accessdate=2022-02-11 |archive-date=16 February 2021 |archive-url=https://web.archive.org/web/20210216084014/https://www.youtube.com/watch/ndMKTnSRsKM |url-status=live }}</ref><ref>{{cite web|url = https://grist.org/living/the-greatest-mystery-of-sloth-pooping-has-been-solved/|title = The greatest mystery of sloth pooping has been solved|date = 23 January 2014|access-date = 9 February 2021|archive-date = 27 January 2021|archive-url = https://web.archive.org/web/20210127220611/https://grist.org/living/the-greatest-mystery-of-sloth-pooping-has-been-solved/|url-status = live}}</ref><ref>{{Cite journal |last1=Pauli |first1=Jonathan N. |last2=Mendoza |first2=Jorge E. |last3=Steffan |first3=Shawn A. |last4=Carey |first4=Cayelan C. |last5=Weimer |first5=Paul J. |last6=Peery |first6=M. Zachariah |date=7 March 2014 |title=A syndrome of mutualism reinforces the lifestyle of a sloth |journal=Proceedings of the Royal Society |publisher=[[Royal Society|The Royal Society Publishing]] |volume=281 |issue=1778|doi=10.1098/rspb.2013.3006 |pmid=24452028 |doi-access=free |pmc=3906947 }}</ref> Recent research shows that moths, which live in the sloth's fur, lay eggs in the sloth's feces. When they hatch, the larvae feed on the feces, and when mature fly up onto the sloth above. These moths may have a [[symbiosis|symbiotic]] relationship with sloths, as they live in the fur and promote growth of algae, which the sloths eat.<ref name="gizmodo" /> Individual sloths tend to spend the bulk of their time feeding on a single "modal" tree; by burying their excreta near the trunk of that tree, they may also help nourish it.<ref name="Community">{{cite encyclopedia|last = Montgomery|first = Sy|title = Community Ecology of the Sloth|encyclopedia = Cecropia: Supplemental Information|publisher = [[Encyclopædia Britannica]]|url = http://www.britannica.com/EBchecked/topic/101053/cecropia/101053suppinfo/Supplemental-Information|access-date = 2009-09-06|archive-date = 24 May 2009|archive-url = https://web.archive.org/web/20090524011902/http://www.britannica.com/EBchecked/topic/101053/cecropia/101053suppinfo/Supplemental-Information|url-status = live}}</ref>

=== Reproduction ===
The pale- and brown-throated three-toed sloths mate seasonally, while the maned three-toed sloth breeds at any time of the year. The reproduction of pygmy three-toed sloths is currently unknown. Litters are of one newborn only, after six months' [[gestation]] for three-toed, and 12 months for two-toed. Newborns stay with their mother for about five months. In some cases, young sloths die from a fall indirectly because the mothers prove unwilling to leave the safety of the trees to retrieve the young.<ref>{{Cite journal|last1=Soares|first1=C. A.|last2=Carneiro|first2=R. S.|date=2002-05-01|title=Social behavior between mothers × young of sloths Bradypus variegatus SCHINZ, 1825 (Xenarthra: Bradypodidae)|journal=Brazilian Journal of Biology|volume=62|issue=2|pages=249–252|doi=10.1590/S1519-69842002000200008|pmid=12489397|issn=1519-6984|doi-access=free}}</ref> Females normally bear one baby every year, but sometimes sloths' low level of movement actually keeps females from finding males for longer than one year.<ref>{{Cite journal|last1=Pauli|first1=Jonathan N.|last2=Peery|first2=M. Zachariah|date=2012-12-19|title=Unexpected Strong Polygyny in the Brown-Throated Three-Toed Sloth|journal=PLOS ONE|volume=7|issue=12|pages=e51389|doi=10.1371/journal.pone.0051389|issn=1932-6203|pmc=3526605|pmid=23284687|bibcode=2012PLoSO...751389P|doi-access=free}}</ref> Sloths are not particularly [[Sexual dimorphism|sexually dimorphic]] and several zoos have received sloths of the wrong sex.<ref>{{cite news|title=Manly secret of non-mating sloth at London Zoo|url=https://www.bbc.co.uk/news/uk-england-london-11031719|website=BBC News|publisher=BBC|access-date=30 April 2015|date=19 August 2010|archive-date=19 September 2020|archive-url=https://web.archive.org/web/20200919145639/https://www.bbc.co.uk/news/uk-england-london-11031719|url-status=live}}</ref><ref>{{cite news|title=Same-sex sloths dash Drusillas breeding plan|url=https://www.bbc.co.uk/news/uk-england-sussex-25233287|website=BBC News|publisher=BBC|access-date=30 April 2015|date=5 December 2013|archive-date=5 December 2020|archive-url=https://web.archive.org/web/20201205134604/https://www.bbc.co.uk/news/uk-england-sussex-25233287|url-status=live}}</ref>

The average lifespan of two-toed sloths in the wild is currently unknown due to a lack of full-lifespan studies in a natural environment.<ref>{{cite web |title=About the Sloth |url=https://slothconservation.com/about-the-sloth/overview/ |website=Sloth Conservation Foundation |access-date=31 October 2019 |archive-date=16 January 2021 |archive-url=https://web.archive.org/web/20210116142251/https://slothconservation.com/about-the-sloth/overview/ |url-status=live }}</ref> Median life expectancy in human care is about 16 years and one individual at the [[Smithsonian Institution|Smithsonian Institution's]] [[National Zoological Park (United States)|National Zoo]] reached an age of 49 years before her death.<ref>{{cite web|url=https://nationalzoo.si.edu/animals/southern-two-toed-sloth|title=Southern two-toed sloth|website=Smithsonian's National Zoo|language=en|access-date=2019-10-30|date=2016-04-25|archive-date=17 July 2019|archive-url=https://web.archive.org/web/20190717065722/https://nationalzoo.si.edu/animals/southern-two-toed-sloth|url-status=live}}</ref>

==Distribution==
[[File:Bradypus pygmaeus.jpg|thumb|right|Depiction of a [[pygmy three-toed sloth]] (''Bradypus pygmaeus'') ([[Thomas Landseer]], 1825)]]
Although habitat is limited to the tropical rainforests of Central and South America, in that environment sloths are successful. On [[Barro Colorado Island]] in [[Panama]], sloths have been estimated to constitute 70% of the [[biomass]] of arboreal mammals.<ref name="Eisenberg2000"/>{{rp|96}} Four of the six living [[species]] are currently rated "least concern"; the [[Maned sloth|maned three-toed sloth]] (''Bradypus torquatus''), which inhabits Brazil's dwindling [[Atlantic Forest]], is classified as "vulnerable",<ref name="iucn B torquatus">{{Cite iucn | author = Chiarello, A. | author2 = Moraes-Barros, N. | name-list-style = amp | title = ''Bradypus torquatus'' | volume = 2014 | page = e.T3036A47436575 | date = 2014 | doi = 10.2305/IUCN.UK.2014-1.RLTS.T3036A47436575.en }}</ref> while the island-dwelling [[pygmy three-toed sloth]] (''B. pygmaeus'') is [[critically endangered]]. Sloths' lower metabolism confines them to the tropics, and they adopt thermoregulation behaviors of cold-blooded animals such as sunning themselves.<ref>{{cite news |last1=Dowling |first1=Stephen |title=Why do sloths move so slowly? |url=http://www.bbc.com/future/story/20190828-why-do-sloths-move-so-slowly |access-date=2 September 2019 |work=BBC Future |publisher=BBC News |date=29 August 2019 |archive-date=12 September 2019 |archive-url=https://web.archive.org/web/20190912112900/http://www.bbc.com/future/story/20190828-why-do-sloths-move-so-slowly |url-status=live }}</ref>

== Human relations ==
[[File:SlothDWA.jpg|thumb|left|[[Three-toed sloth]] in the [[Dallas World Aquarium]]]]The majority of recorded sloth deaths in [[Costa Rica]] are due to contact with [[Electric power transmission|electrical lines]] and [[poaching|poachers]]. Their claws also provide another, unexpected deterrent to human hunters; when hanging upside-down in a tree, they are held in place by the claws themselves and often do not fall down even if shot from below.

Sloths are victims of animal trafficking where they are sold as pets. However, they generally make very poor pets, as they have such a specialized ecology.<ref>{{cite web|url=https://abcnews.go.com/International/hottest-selling-animal-colombias-illegal-exotic-pet-trade/story?id=19172620|title=Sloths: Hottest-Selling Animal in Colombia's Illegal Pet Trade|date=2013-05-29|website=ABC News|access-date=2017-12-02|archive-date=6 July 2020|archive-url=https://web.archive.org/web/20200706131424/https://abcnews.go.com/International/hottest-selling-animal-colombias-illegal-exotic-pet-trade/story?id=19172620|url-status=live}}</ref>
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==References==
{{reflist}}

== Further reading==
*  Rauch, Alan. ''Sloth'' (Reaktion Books,  2023) [http://www.h-net.org/reviews/showrev.php?id=60399 Online review of this book.]

==External links==
{{Americana Poster}}
* {{Wiktionary-inline}}

{{Pilosa}}
{{Pilosan genera|P.|state=autocollapse}}
{{Taxonbar|from=Q2274076}}
{{Authority control}}

[[Category:Sloths| ]]
[[Category:Clawed herbivores]]
[[Category:Folivores]]
[[Category:Pilosa]]
[[Category:Extant Rupelian first appearances]]