View source for Pygmy three-toed sloth

{{Short description|Species of mammals related to anteaters and armadillos}}
{{Good article}}
{{Speciesbox
| name = Pygmy three-toed sloth 
| image = Bradypus pygmaeus.jpg
| image_caption = <!-- 1825 illustration, [[Thomas Landseer]] -->
| status = CR
| status_system = IUCN3.1
| status_ref = <ref name="iucn status 19 November 2021">{{cite iucn |author=Voirin, B. |author2=Smith, D. |author3=Chiarello, A. |author4=Moraes-Barros, N. |date=2014 |title=''Bradypus pygmaeus'' |page=e.T61925A47444229 |doi=10.2305/IUCN.UK.2014-1.RLTS.T61925A47444229.en |access-date=19 November 2021}}</ref>
| status2 = CITES_A2 
| status2_system = CITES 
| status2_ref = <ref>{{Cite web|title=Appendices {{!}} CITES|url=https://cites.org/eng/app/appendices.php|access-date=2022-01-14|website=cites.org}}</ref>
| genus = Bradypus
| species = pygmaeus
| authority = [[species:Robert P. Anderson|Anderson]] & [[Charles O. Handley|Handley]], 2001
| range_map = Pygmy Three-toed Sloth area.png
| range_map_caption = Range of the pygmy three-toed sloth 
}}

The '''pygmy three-toed sloth''' ('''''Bradypus pygmaeus'''''), also known as the '''monk sloth''' or '''dwarf sloth''', is a [[species]] of [[sloth]] in the [[Family (biology)|family]] [[Bradypodidae]]. The species is [[Endemism|endemic]] to [[Isla Escudo de Veraguas]], a small island off the [[Caribbean]] coast of [[Panama]]. The species was first [[Species description|described]] by [[Robert P. Anderson (zoologist)|Robert P. Anderson]] of the [[University of Kansas]] and [[Charles O. Handley|Charles O. Handley Jr.]], of the [[Smithsonian Institution]] in 2001. The pygmy three-toed sloth is significantly smaller than the other three members of its [[genus]], but otherwise resembles the [[brown-throated three-toed sloth]]. According to Anderson and Handley Jr., the head-and-body length is between {{convert|48|and|53|cm|in}}, and the body mass ranges from {{convert|2.5|to|3.5|kg|abbr=on}}.

This sloth, like other sloths, is [[arboreal]] (tree-living) and feeds on leaves. It has a body adapted to hang by its limbs; the large curved claws help the sloth to keep a strong grip on tree branches. It lives high in the canopy but descends once a week to defecate on the forest floor.<ref>{{Cite web|url=https://onekindplanet.org/animal/sloth-three-toed/|title=Amazing Facts about the Three Toed Sloth {{!}} OneKindPlanet Education|website=OneKindPlanet|language=en-GB|access-date=2019-06-12}}</ref> It is [[symbiosis|symbiotically]] associated with [[green algae]], that can provide it with a [[camouflage]]. Details of mating behavior and reproduction have not been documented. The pygmy three-toed sloth is found exclusively in the [[Rhizophora mangle|red mangrove]]s of Isla Escudo de Veraguas, restricted to an area of {{convert|4.3|sqkm|sqmi}}. A 2012 census of pygmy three-toed sloths estimated the total population at 79. The [[IUCN]] lists the pygmy three-toed sloth as [[Critically endangered species|critically endangered]] and they are listed on [[the world's 100 most threatened species]].

==Discovery and taxonomy==
The pygmy three-toed sloth was first [[Species description|described]] by Robert P. Anderson of the [[University of Kansas]] and Charles O. Handley Jr., of the [[Smithsonian Institution]] in 2001. The researchers noted that the [[three-toed sloth]]s found on Isla Escudo de Veraguas were significantly smaller than those that occur on the nearby outer islands of [[Bocas del Toro Province]]. Moreover, they differ from other populations in terms of [[pelage]] and [[cranium|cranial]] characteristics. Hence, they considered the three-toed sloths in Isla Escudo de Veraguas to be an independent species and formally described it from the skin and skull of an adult female. The researchers further pointed out that Isla Escudos de Veraguas is the oldest island and located farthest from the mainland, which began breaking up into small islands due to rises in sea levels 10,000 years ago. They proposed that this species evolved from an isolated population that had originated from the mainland population of [[brown-throated three-toed sloth]]s; it gradually differentiated enough to become an independent species through [[insular dwarfism]].<ref name="Anderson">{{Cite journal| last1 = Anderson | first1 = R.P. | author-link=species:Robert P. Anderson |last2 = Handley Jr. | first2 = C. O.| author2-link=Charles O. Handley |title = A new species of three-toed sloth (Mammalia: Xenarthra) from Panama, with a review of the genus ''Bradypus''| journal = [[Proceedings of the Biological Society of Washington]]| volume = 114 | issue = 1 | pages = [https://archive.org/details/proceedingsofb1142001biol/page/n6 1]–33| date = 2001| url = https://archive.org/details/proceedingsofb1142001biol }} {{open access}}</ref> In another study the following year, the researchers observed that the mean body size of three-toed sloths on an island decreases linearly as the age of the island increases; the area of the island and the distance from the mainland, however, do not appear to significantly affect dwarfing.<ref name= "Anderson2">{{Cite journal | last1 = Anderson | first1 = R.P. | last2= Handley Jr. |first2= C.O.| title = Dwarfism in insular sloths: biogeography, selection, and evolutionary rate| journal = [[Evolution (journal)|Evolution]]| volume = 56 | issue = 5 | pages = 1045–58 | date = 2002| doi = 10.1111/j.0014-3820.2002.tb01415.x | pmid = 12093018 | s2cid = 12803566 | url = https://www.researchgate.net/publication/11282772| doi-access = free }} {{open access}}</ref>

The pygmy three-toed sloth is one of the four extant members of the genus ''[[Three-toed sloth|Bradypus]]'', and is classified under the family [[Bradypodidae]].<ref name=msw3>{{MSW3 Pilosa | id = 11800005 | page = 100}}</ref> According to molecular phylogenetic analysis, Bradypodidae nests with [[Megalonychidae]], [[Megatheriidae]] and [[Nothrotheriidae]] in the sloth superfamily Megatherioidea.<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|hdl= 11336/136908|hdl-access= free}}</ref><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}}</ref> The [[Generic name (biology)|generic name]] ''Bradypus'' is the combination of two [[Greek language|Greek]] words: ''brady'' ("slow") and ''pous'' ("foot").<ref>{{MerriamWebsterDictionary|Bradypus|access-date=28 May 2016}}</ref> The [[specific name (zoology)|specific name]] ''pygmaeus'' comes from the Greek ''pugmaios'' ("as small as a fist").<ref name="beddard">{{cite book|last1=Beddard|first1=F.E.|title=The Cambridge Natural History, Vol X. Mammalia|date=2015|publisher=The Library of Alexandria|isbn=978-1-5115-9533-9}}</ref> 'Monk sloth' and 'dwarf sloth' are two other names for this sloth.<ref name=Hayssen2008>{{cite journal | last = Hayssen | first = V. | year = 2008 | title = ''Bradypus pygmaeus'' (Pilosa: Bradypodidae) | journal = [[Mammalian Species]] | volume = 812 | pages = 1–4 | doi = 10.1644/812.1 | s2cid = 84387124 | url = https://zenodo.org/record/5033371 }} {{open access}}</ref>

== Characteristics ==
[[File:Perezoso La Mochila.jpg|thumb|Pygmy three-toed sloth on Isla Escudo de Veraguas]]
The pygmy three-toed sloth is significantly smaller than the other members of its genus, but otherwise resembles the brown-throated sloth. According to Anderson and Handley Jr., the head-and-body length is between {{convert|48|and|53|cm|in}}, and the body mass ranges from {{convert|2.5|to|3.5|kg|abbr=on}}. The brown-throated sloth is nearly 40% heavier and 15% smaller in head-and-body length than the pygmy three-toed sloth. Moreover, the brown-throated sloth is lighter on the crown. The face is buff to tan; a dark band runs across the brow, surrounded by an orange patch. The throat is gray to brown, lighter than the underbelly; the dark brown back is spotted and has a dark stripe along the midline. Facial hair is short, while the long, rough hair on the [[Crown (anatomy)|crown]] and shoulders forms a hood. The grayish limbs have three claws each. The tail is {{convert|4.5|to|6|cm|in}} long.<ref name=Anderson/><ref name=Anderson2/><ref name="Reid">{{cite book|last1=Reid|first1=F.A.|title=A Field Guide to the Mammals of Central America & Southeast Mexico|date=2009|publisher=Oxford University Press|location=Oxford, UK|isbn=978-0-19-534322-9|page=59|edition=2nd|url={{Google Books|id=aBEbUaXTWYAC|plainurl=yes|}}}}</ref>

They have a relatively small and slender skull, with a large [[external auditory meatus]], narrow [[squamosal]] and [[mandibular process]]es, a minuscule [[stylomastoid foramen]], and usually lack foramina for the [[external carotid artery]] and anterodorsal (meaning in front and toward the back) [[nasopharynx]]. The [[dental formula]] of three-toed sloths is: {{DentalFormula|upper=5|lower=4–5}}<ref>{{cite book|last1=Ungar|first1=P.S.|title=Mammal Teeth: Origin, Evolution, and Diversity|date=2010|publisher=Johns Hopkins University Press|location=Baltimore, US|isbn=9780801899515|pages=145–6|url={{Google Books|id=BGGTYS2AgncC|page=145|plainurl=yes}}}}</ref> Two of the teeth in each jaw are [[Incisor tooth|incisor]]-like, although those in the upper jaw are small or may be absent. Many of the features found in pygmy sloths are thought to be indicative of a relatively rapid evolution of a new species in an isolated, island habitat.<ref name="Anderson"/>

They host algae inside their fur which causes them to have a greenish color. The algae is generally more noticeable on the top of their head and neck, dorsal portions of the forelimbs, and upper backside.<ref>{{Cite journal|last=Voirin|first=Bryson|date=2015-08-03|title=Biology and conservation of the pygmy sloth, Bradypus pygmaeus|url=https://academic.oup.com/jmammal/article-lookup/doi/10.1093/jmammal/gyv078|journal=Journal of Mammalogy|language=en|volume=96|issue=4|pages=703–707|doi=10.1093/jmammal/gyv078|issn=0022-2372}}</ref>

==Distribution and status==
[[File:Rhizophora yngtree.jpg|thumb|right|Pygmy three-toed sloths live on [[Rhizophora mangle|red mangrove]]s.]]
The pygmy three-toed sloth is unique in that it is found exclusively in the [[Rhizophora mangle|red mangrove]]s of [[Isla Escudo de Veraguas]]; the island has a small area of approximately {{convert|4.3|sqkm|sqmi}}. A 2012 census of pygmy three-toed sloths estimated the total population at 79 – of which 70 occurred on mangroves and 9 in the surroundings. The population density was calculated as {{convert|5.8|/ha|/acre|abbr=off}}. The total area occupied by mangroves on the island was estimated to be around {{convert|10.67|ha|sqmi}}.<ref>{{cite journal|last1=Kaviar|first1=S.|last2=Shockey|first2=J.|last3=Sundberg|first3=P.|last4=Evans|first4=A.R.|title=Observations on the endemic pygmy three-toed sloth, ''Bradypus pygmaeus'' of Isla Escudo de Veraguas, Panamá|journal=[[PLOS ONE]]|date=2012|volume=7|issue=11|pages=e49854|doi=10.1371/journal.pone.0049854|pmid=23185461|pmc=3504081|bibcode=2012PLoSO...749854K|doi-access=free}} {{open access}}</ref> While their population has presumably always been low due to their restricted range, the 2012 census found far lower numbers than had been estimated (less than 500) by the [[IUCN]] in 2010.<ref name=portrait>{{cite web | url = http://www.iucn.org/themes/ssc/redlist2006/portraits_in_red.htm#sloth | title = Portraits in Red | access-date = 1 January 2008 | work = [[IUCN Red List]] |archive-url = https://web.archive.org/web/20071213200225/http://www.iucn.org/themes/ssc/redlist2006/portraits_in_red.htm#sloth <!-- Bot retrieved archive --> |archive-date = 13 December 2007}}</ref>

The IUCN lists the pygmy three-toed sloth as [[Critically endangered species|critically endangered]]; it is also listed in [[CITES Appendix II]]. According to the IUCN, conservation efforts are being hampered by conflict between local peoples and the government.<ref name="iucn status 19 November 2021" /> Threats to the sloth's survival include timber harvesting and human settlement, that might lead to habitat degradation.<ref>{{cite journal|last1=Voirin|first1=B.|title=Biology and conservation of the pygmy sloth, ''Bradypus pygmaeus''|journal=Journal of Mammalogy|date=2015|volume=96|issue=4|pages=703–7|doi=10.1093/jmammal/gyv078|s2cid=73534122}}</ref> After several observations, the corpses of the pygmy three-toed sloth were found to be unharmed physically, suggesting that predation is not a major threat. Instead, disease, habitat loss, or natural causes were larger factors in the species’ death. A study in 2011 showed that there were 79 pygmy sloths in the wild. Studies in 2010 and 2013 suggested a recent [[population bottleneck]] and decline in [[genetic variability]].<ref name="iucn status 19 November 2021" />

== Ecology and behavior ==
The pygmy three-toed sloth, like others in its genus, is an [[arboreal]] (tree-living) animal. This sloth can spend as many as 15 to 20 hours per day on trees. It moves at an extremely slow speed of {{convert|0.15|mph|km/h|order=flip}}, making it one of the slowest animals.<ref>{{cite book|last1=Hearst|first1=M.|title=Unusual Creatures: A Mostly Accurate Account of some of the Earth's Strangest Animals|date=2012|publisher=Chronicle Books LLC|location=San Francisco, US|isbn=978-1-4521-1985-4|page=82|url={{Google Books|id=tS1FLyPj2BkC|page=93|plainurl=yes}}}}</ref> The pygmy three-toed sloth is [[symbiosis|symbiotically]] related to [[green algae]]; a 2010 study investigated this in detail. Different sloths harbour different types of algae – only ''[[Tricophilus]]'' species were found on the brown-throated and pygmy three-toed sloths. These algae discolor the fur of the sloth, giving it a greenish hue – this serves as an efficient [[Camouflage animals|camouflage]].<ref>{{cite journal|last1=Suutari|first1=M.|last2=Majaneva|first2=M.|last3=Fewer|first3=D.P|last4=Voirin|first4=B.|last5=Aiello|first5=A.|last6=Friedl|first6=T.|last7=Chiarello|first7=A.G|last8=Blomster|first8=J.|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|date=2010|volume=10|issue=1|pages=86|doi=10.1186/1471-2148-10-86|pmid=20353556|pmc=2858742 |doi-access=free |bibcode=2010BMCEE..10...86S }}} {{open access}}</ref> Some of these algae might be transferred to offspring through the mother, others may be picked up from the surroundings over time.<ref>{{cite book|last1=Feldhamer|first1=G.A.|last2=Drickamer|first2=L.C.|last3=Vessey|first3=S.H.|last4=Merritt|first4=J.F.|last5=Krajewski|first5=C.|title=Mammalogy: Adaptation, Diversity, Ecology|date=2015|publisher=JHU Press |isbn=978-1-4214-1588-8|edition=4th|url={{Google Books|id=Ugq5BgAAQBAJ|plainurl=yes|page=343}}}}</ref> The smaller size of pygmy sloths reduces their energy requirements for survival and reproduction, making them an apparent example of [[insular dwarfism]].<ref name= "Anderson2"/> A BBC documentary, in which English naturalist [[Chris Packham]] recognizes the pygmy three-toed sloth as the first in his list of the top ten discoveries in the 2000s, shows a rare clip of a swimming pygmy three-toed sloth.<ref>{{cite episode| title = Rare swimming pygmy sloth |  url = http://www.bbc.co.uk/programmes/b00wqfhd | date = 17 March 2011 | series = Decade of Discovery | first = C. | last = Packham | author1-link= Chris Packham | publisher = [[BBC Two]] | access-date = 28 May 2016| time = 51:56}}</ref>

Like other sloths, the pygmy three-toed sloth feeds on leaves. It feeds on red mangrove leaves, which are relatively poor in nutrients and coarser than the tender leaves of ''[[Cecropia]]'' species eaten by brown-throated sloths on the mainland.<ref name= "Anderson2"/> Details of mating behavior and reproduction have not been documented.<ref name=Hayssen2008/>

==See also==
*[[Pilosans of the Caribbean]]

== References ==
{{Reflist|30em}}

== External links ==
{{Commons category|Bradypus pygmaeus|Bradypus pygmaeus<br>(Pygmy three-toed sloth)}}
* {{Wikispecies-inline|Bradypus pygmaeus}}
* EDGE of Existence [http://www.edgeofexistence.org/mammals/species_info.php?id=1396 Saving the World's most Evolutionarily Distinct and Globally Endangered (EDGE) species]

{{Pilosa}}
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{{Taxonbar|from=Q244121}}

[[Category:Critically endangered fauna of North America]]
[[Category:Mammals of the Caribbean]]
[[Category:EDGE species]]
[[Category:Endemic fauna of Panama]]
[[Category:Mammals described in 2001]]
[[Category:Mammals of Central America]]
[[Category:Sloths]]