Sloth

{{see also|List of pilosans}}

Sloths belong to the superorder Xenarthra, a group of placental mammals believed to have evolved in the continent of South America around 60 million years ago.{{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}} One study found that xenarthrans broke off from other placental mammals around 100 million years ago.{{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 }} Anteaters and armadillos are also included among Xenarthra. The earliest xenarthrans were arboreal herbivores with sturdy vertebral columns, fused pelvises, stubby teeth, and small brains. Sloths are in the taxonomic suborder Folivora{{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}} 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 (†):

• †Megalocnidae: the Greater Antilles sloths, a basal group that arose about 32 million years ago and became extinct about 5,000 years ago.
• Superfamily Megatherioidea
• Bradypodidae, the three-toed sloths, contains four extant species:
• The brown-throated three-toed sloth (Bradypus variegatus) is the most common of the extant species of sloth, which inhabits the Neotropical realm{{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

}} in the forests of South and Central America.

• The 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.{{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 }}
• The 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 sloths, 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{{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 }} in the north to western Ecuador in the south, and the other in eastern Peru, western Brazil, and northern Bolivia.{{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 }}
• †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.

File:Megatherium americanum Skeleton NHM.JPG (Megatheriidae, London)]]

File:Nothrotheriops shastensis La Brea.jpg (Nothrotheriidae, La Brea)]]

The common ancestor of the two existing sloth genera dates to about 28 million years ago, 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".{{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}} 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.{{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}}

File:Megalonyx wheatleyi skeleton & restoration.jpg (Megalonychidae) fossil (AMNH) and restoration]]

File:San Diego Paramylodon.jpg (Mylodontidae, 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 to the Greater Antilles by the Oligocene, and that the megalonychid Pliometanastes and the 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 nothrotheriid Thalassocnus of the west coast of South America became adapted to a semiaquatic and, eventually, perhaps fully aquatic marine lifestyle.{{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}} 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 seagrasses, similar to the extant sirenians.{{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}}

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 Greater Antilles sloths.{{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

}} 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.{{cite journal|last1=Gaudin|first1=Timothy|title=Phylogenetic Relationships among Sloths (Mammalia, Xenarthra, Tardigrada): The Craniodental Evidence.|journal=Zoological Journal of the Linnean Society|date= 2004|volume= 140|issue= 2|pages= 255–305|doi= 10.1111/j.1096-3642.2003.00100.x|doi-access= free}} Much of the morphological evidence collected to support the hypothesis of diphyly has been based on the structure of the inner ear.{{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 }}

Recently obtained molecular data from collagen{{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}} and mitochondrial DNA sequences{{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}} 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 mylodontids and three-toed sloths within Megatherioidea, close to Megalonyx, megatheriids and nothrotheriids. 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 branch of the sloth evolutionary tree.

The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data.

{{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

}}

}}

}}

}}

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).{{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}}

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. 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.{{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=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}}

File:MC Drei-Finger-Faultier.jpg (Bradypus variegatus), Cahuita National Park, Costa Rica]]

File:Ground_sloth_size_comparison.png compared to a human, including 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 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.{{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}} 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 mammals 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 manatees, with six.{{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 }}

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.{{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}}

Sloths have very low 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.

Brown-throathed and Hoffman's two-toed sloths use their forelimbs as their principal means of propulsion and their skeletal muscle have very high proportions of oxidative slow twitch (Type I) muscle fibers, with high activity of the anaerobic enzyme 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.{{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}} Forelimb muscle mass makes up only 5.1 % of total body weight in the brown-throated sloth.{{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}}

The outer hairs of sloth fur grow in a direction opposite from that of other mammals. In most mammals, hairs grow toward the 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{{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 }} from predatory jaguars, ocelots,{{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=}} and harpy eagles.{{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}} Because of the algae, sloth fur is a small ecosystem of its own, hosting many species of commensal and parasitic arthropods.{{Cite journal|last1=Gilmore|first1=D. P.|last2=Da Costa|first2=C. P.|last3=Duarte|first3=D. P. F.|date=2001-01-01|title=Sloth biology: an update on their physiological ecology, behavior and role as vectors of arthropods and arboviruses|journal=Brazilian Journal of Medical and Biological Research|volume=34|issue=1|pages=9–25|doi=10.1590/S0100-879X2001000100002|issn=0100-879X|pmid=11151024|doi-access=free}} There are a large number of arthropods associated with sloths. These include biting and blood-sucking flies such as mosquitoes and sandflies, triatomine bugs, lice, ticks and mites. Sloths have a highly specific community of commensal beetles, mites and moths.{{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}} The species of sloths recorded to host arthropods include 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.{{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}}

Their 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.{{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}} Their specialised hands and feet have long, curved claws to allow them to hang upside down from branches without effort,{{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}} 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.

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.{{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}}

Sloths are surprisingly strong swimmers and can reach speeds of {{cvt|13.5|m}} per minute.{{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}} They use their long arms to paddle through the water and can cross rivers and swim between islands.{{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}} 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.{{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}}

Wild brown-throated three-toed sloths sleep on average 9.6 hours a day.{{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}} Two-toed sloths are nocturnal.{{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 (see pp. 94–95, 97)|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}} Three-toed sloths are mostly nocturnal but can be active in the day. They spend 90 per cent of their time motionless.

Sloths are solitary animals that rarely interact with one another except during breeding season,{{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 }} though female sloths do sometimes congregate, more so than do males.{{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 }}

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: 1) fertilize trees when feces are deposited at the base of the tree;Montgomery, G. G., & Sunquist, M. E. (1975). Impact of Sloths on Neotropical Forest Energy Flow and Nutrient Cycling. Ecological Studies, 69–98. DOI:10.1007/978-3-642-88533-4_7 2) cover feces and avoid predation;Bailey, T. N. (1974). Social organization in a bobcat population. The Journal of Wildlife Management, 38(3),435-446.Liberg, O. (1980). Spacing patterns in a population of rural free roaming domestic cats. Oikos, 32(3),336-349.Pauli, J. N., Mendoza, J. E., Steffan, S. A., Carey, C. C., Weimer, P. J., & Peery, M. Z. (2014). A syndrome of mutualism reinforces the lifestyle of a sloth. Proceedings of the Royal Society B: Biological Sciences, 281(1778), 20133006. DOI: 10.1098/rspb.2013.3006 3) chemical communication between individuals;Chiarello, A. G. (2008). Sloth ecology: an overview of field studies. The biology of the Xenarthra, 269-280. 4) pick up trace nutrients in their claws, that are then ingested;Voirin, B., Kays, R., Wikelski, M., & Lowman, M. (2013). Why Do Sloths Poop on the Ground? In M. Lowman, S. Devy, & T. Ganesh (eds). Treetops at Risk(pp. 195-199). Springer, New York, NY. and 5) favor a mutualistic relationship with populations of fur moths. 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.Monge Nájera, J. (2021). Why sloths defecate on the ground: rejection of the mutualistic model. UNED Research Journal, 13(1), 4-4.

File:Two-toed sloth Costa Rica - cropped.jpg (Choloepus hoffmanni) feeding in Manuel Antonio National Park in Costa Rica]]Baby sloths learn what to eat by licking the lips of their mother.{{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}} 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, 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. As much as two-thirds of a well-fed sloth's body weight consists of the contents of its stomach, and the 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.{{cite web |url=https://www.youtube.com/watch/ndMKTnSRsKM |title=The 'Busy' Life of the Sloth | 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 }}{{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}}{{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=The Royal Society Publishing |volume=281 |issue=1778|doi=10.1098/rspb.2013.3006 |pmid=24452028 |doi-access=free |pmc=3906947 }} 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 symbiotic relationship with sloths, as they live in the fur and promote growth of algae, which the sloths eat. 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.{{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}}

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.{{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}} 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.{{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}} Sloths are not particularly sexually dimorphic and several zoos have received sloths of the wrong sex.{{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}}{{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}}

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.{{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 }} Median life expectancy in human care is about 16 years and one individual at the Smithsonian Institution's National Zoo reached an age of 49 years before her death.{{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}}

File:Bradypus pygmaeus.jpg (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.{{Cite book|url=https://books.google.com/books?id=p2MDAzCeQQoC&pg=PA96|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 (see p. 96)|oclc=493329394|access-date=25 September 2016|archive-date=19 September 2020|archive-url=https://web.archive.org/web/20200919145723/https://books.google.com/books?id=p2MDAzCeQQoC&pg=PA96|url-status=live}} Four of the six living species are currently rated "least concern"; the maned three-toed sloth (Bradypus torquatus), which inhabits Brazil's dwindling Atlantic Forest, is classified as "vulnerable",{{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 }} 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.{{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 }}

File:SlothDWA.jpg in the Dallas World Aquarium]]The majority of recorded sloth deaths in Costa Rica are due to contact with electrical lines and 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.{{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}}

The Sloth Institute Costa Rica is known for caring, rehabilitating and releasing sloths back into the wild.{{cite web|url=http://www.theslothinstitutecostarica.org|title=The Sloth Institute website|access-date=23 March 2022|archive-date=31 March 2021|archive-url=https://web.archive.org/web/20210331090928/http://www.theslothinstitutecostarica.org/|url-status=live}} Also in Costa Rica, the Aviarios Sloth Sanctuary cares for sloths. It has rehabilitated and returned about 130 individuals to the wild.{{Cite news

| author = Sevcenko, Melanie

| title = Sloth sanctuary nurtures animals back to health

| work = Deutsche Welle

| access-date = 2013-04-18

| date = 2013-04-17

| url = http://www.dw.de/sloth-sanctuary-nurtures-animals-back-to-health/a-16750190

| archive-date = 13 May 2015

| archive-url = https://web.archive.org/web/20150513014722/http://www.dw.de/sloth-sanctuary-nurtures-animals-back-to-health/a-16750190

| url-status = live

}} However, a report in May 2016 featured two former veterinarians from the facility who were critical of the sanctuary's efforts, accusing it of mistreating the animals.{{cite news | author = Schelling, Ameena | title = Famous Sloth Sanctuary Is A Nightmare For Animals, Ex-Workers Say | work = The Dodo | access-date = 2016-05-20 | date = 2016-05-19 | url = https://www.thedodo.com/sloths-sanctuary-nightmare-1807794384.html | archive-date = 18 January 2021 | archive-url = https://web.archive.org/web/20210118081459/https://www.thedodo.com/sloths-sanctuary-nightmare-1807794384.html | url-status = live }}

{{reflist}}

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

{{Americana Poster}}

• {{Wiktionary-inline}}
• {{Commons category-inline|Folivora}}
• {{Wikispecies-inline|Folivora}}

{{Pilosa}}

{{Pilosan genera|P.|state=autocollapse}}

{{Taxonbar|from=Q2274076}}

{{Authority control}}

Category:Clawed herbivores

Category:Folivores

Category:Pilosa

Category:Extant Rupelian first appearances