two-toed sloth

{{Species table |genus=Choloepus |authority-name=Illiger |authority-year= 1811 |species-count=two|no-note=y|narrow-percent=75}}

{{Species table/row

|name= Linnaeus's two-toed sloth|binomial=Choloepus didactylus

|image=File:Cholepus didactylus - Flickr - Dick Culbert.jpg |image-size=180px |image-alt=

|authority-name=Linnaeus|authority-year= 1758 |authority-not-original=yes

|range= Northern South America, found in Venezuela, the Guyanas, Colombia, Ecuador, Peru, and Brazil north of the Amazon River

|range-image=File:Linné's Two-toed Sloth area.png

|range-image-size=180px

|size=

|habitat=

|hunting=

|iucn-status= LC

|population=

|direction=

|subspecies=

}}

{{Species table/row

|name= Hoffmann's two-toed sloth|binomial=Choloepus hoffmanni

|image=File:Choloepus hoffmanni (Puerto Viejo, CR) crop.jpg |image-size=180px |image-alt=

|authority-name=Peters|authority-year= 1858 |authority-not-original=

|range= Central America and northwestern South America

|range-image=File:Hoffmann's Two-toed Sloth area.png

|range-image-size=180px

|size=

|habitat=

|hunting=

|iucn-status= LC

|population=

|direction=

|subspecies={{Collapsible list |expand=yes |title=Five subspecies |bullets=on

|C. h. hoffmanni, Peters, 1858 – Honduras, Nicaragua, Costa Rica, Panama

|C. h. agustinus, Allen, 1913 – Venezuela, western Colombia, northern Ecuador

|C. h. capitalis, Allen, 1913 – western Ecuador

|C. h. juruanus, Lönnberg, 1942 – Brazil, Bolivia, extreme eastern Peru

|C. h. pallescens, Lönnberg, 1928 – Peru

}}

}}

{{Species table/end}}

A study of retrovirus and mitochondrial DNA suggests that C. didactylus and C. hoffmani diverged 6 to 7 million years ago.{{cite journal|last1=Slater|first1=G. J.|last2=Cui|first2=P.|last3=Forasiepi|first3=A. M.|last4= Lenz|first4=D.|last5= Tsangaras|first5=K.|last6= Voirin|first6=B.|last7=de Moraes-Barros|first7=N.|last8= MacPhee|first8=R. D. E.|last9=Greenwood|first9=A. D.|title=Evolutionary Relationships among Extinct and Extant Sloths: The Evidence of Mitogenomes and Retroviruses|journal=Genome Biology and Evolution|volume= 8|issue=3|date= 2016-02-14|pages= 607–621|doi= 10.1093/gbe/evw023|pmid=26878870|pmc=4824031}} Furthermore, based on cytochrome c oxidase subunit I sequences, a similar divergence date ({{circa|7 million}} years ago) between the two populations of C. hofmanni separated by the Andes has been reported.{{cite journal|last1=Moraes-Barros|first1=N.|last2=Arteaga|first2=M. C.|title=Genetic diversity in Xenarthra and its relevance to patterns of neotropical biodiversity|journal=Journal of Mammalogy|volume= 96|issue=4|date= 2015-06-01|pages= 690–702|doi= 10.1093/jmammal/gyv077|doi-access=free}} Their ancestors evolved with marine vertebrae, the three toed-sloth and the manatee are the only other mammals with similar vertebrae.{{Cite journal |last1=Muizon |first1=C. de |last2=McDonald |first2=H. G. |date=May 1995 |title=An aquatic sloth from the Pliocene of Peru |url=https://www.nature.com/articles/375224a0 |journal=Nature |language=en |volume=375 |issue=6528 |pages=224–227 |doi=10.1038/375224a0 |bibcode=1995Natur.375..224M |s2cid=4369283 |issn=1476-4687}}

Both types of 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. Although similar in overall appearance, the relationship between the two genera is not close. Recent phylogenetic analyses{{cite journal

| last = Hoss

| first = Matthias

|author2=Dilling, Amrei |author3=Currant, Andrew |author4=Paabo, Svante

| title = Molecular phylogeny of the extinct ground sloth Mylodon darwinii

| journal = Proceedings of the National Academy of Sciences

| volume = 93

| issue = 1

| pages = 181–185

| date = 9 Jan 1996

| pmid = 8552600 | doi=10.1073/pnas.93.1.181 | pmc=40202| bibcode = 1996PNAS...93..181H

| doi-access = free

}} support analysis of morphological data from the 1970s and 1980s, indicating the two genera are not closely related and adapted to their arboreal lifestyles independently. It was unclear from this work from which ground-dwelling sloth taxa the three-toed sloths evolved. Based on the morphological comparisons, it was thought the two-toed sloths nested phylogenetically within one of the divisions of Caribbean sloths.{{Cite book | last1= White | first1 = J.L.| last2= MacPhee | first2 = R.D.E.

| title = Biogeography of the West Indies: Patterns and Perspectives

| editor1-last = Woods | editor1-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}} 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 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|pages=184|year=2014|last1=Raj Pant|first1=Sara|last2=Goswami|first2=Anjali|last3=Finarelli|first3=John A |issue=1 |doi-access=free |bibcode=2014BMCEE..14..184R }} Most morphological studies have concluded that convergent evolution is the mechanism that resulted in today's two genera of tree sloths. This means that the extant genera evolved analogous traits, such as locomotion methods, size, habitat, and many other traits independently from one another as opposed to from their last common ancestor. This makes tree sloths “one of the most striking examples of convergent evolution known among mammals”.

Recently obtained molecular data from collagen and mitochondrial DNA sequences 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 the Caribbean sloths being moved out of that family and away from Megalonyx. Caribbean sloths are placed in a separate, basal branch of the sloth evolutionary tree.

{{Phylogeny/Mylodontoidea}}

File:TwoToedSlothDetail.jpg

The name "two-toed sloth" was intended to describe an anatomical difference between the genera Choloepus and Bradypus, but does so in a potentially misleading way. Members of Choloepus have two digits on their forelimbs (the thoracic limbs) and three digits on their hindlimbs (the pelvic limbs), while members of Bradypus have three digits on all limbs. Although the term "two-fingered" sloth is arguably less misleading, the shorter "two-toed" is much more widely used.{{NoteTag|Given that sloths are regarded as quadrupeds, whether their forelimb digits should be described as fingers is debatable.}}

Members of Choloepus are larger than three-toed sloths, having a body length of {{convert|58|to|70|cm|in}}, and weighing {{convert|4|to|8|kg|lb}}. Other distinguishing features include a more prominent snout, longer fur, and the absence of a tail.{{cite book|editor= Macdonald, D.|author= Dickman, Christopher R.|year= 1984|title= The Encyclopedia of Mammals|publisher= Facts on File|location= New York|pages= [https://archive.org/details/encyclopediaofma00mals_0/page/776 776–779]|isbn= 0-87196-871-1|url-access= registration|url= https://archive.org/details/encyclopediaofma00mals_0/page/776}}

Two-toed sloths spend most of their lives hanging upside down from trees. They cannot walk, so they pull hand-over-hand to move around, which is at an extremely slow rate. Almost all of their movement comes from this suspended upside down position, at a higher degree than even three-toed sloths. As a result, they tend to gravitate towards less vertical portions of trees.{{Cite journal |last1=Granatosky |first1=Michael C. |last2=Karantanis |first2=Nikolaos E. |last3=Rychlik |first3=Leszek |last4=Youlatos |first4=Dionisios |date=December 2018 |title=A suspensory way of life: Integrating locomotion, postures, limb movements, and forces in two-toed sloths Choloepus didactylus (Megalonychidae, Folivora, Pilosa): GRANATOSKY et al. |url=https://onlinelibrary.wiley.com/doi/10.1002/jez.2221 |journal=Journal of Experimental Zoology Part A: Ecological and Integrative Physiology |language=en |volume=329 |issue=10 |pages=570–588 |doi=10.1002/jez.2221|pmid=30129260 |s2cid=52050040 }}{{Cite journal |last1=Gilmore |first1=D. P. |last2=Da-Costa |first2=C. P. |last3=Duarte |first3=D. P. F. |date=February 2000 |title=An update on the physiology of two- and three-toed sloths |journal=Brazilian Journal of Medical and Biological Research |language=en |volume=33 |issue=2 |pages=129–146 |doi=10.1590/S0100-879X2000000200001 |pmid=10657054 |issn=0100-879X|doi-access=free }} Being predominantly nocturnal, their fur, which grows greenish algae to blend in, is their main source of protection.[https://www.britannica.com/animal/sloth "sloth."] Encyclopædia Britannica. Their body temperatures depend at least partially on the ambient temperature; they cannot shiver to keep warm, as other mammals do, because of their unusually low metabolic rates and reduced musculature. Two-toed sloths also differ from three-toed sloths in their climbing behavior, preferring to descend head first.

File:Baby Choloepus hoffmanni, Costa Rica.JPG, Costa Rica]]

Two-toed sloths have a gestation period of six months to a year, depending on the species. Their ovarian cycle lasts around 31 to 33 days, independently of the seasons but dependent on the species.{{Cite journal |last1=Troll |first1=S. |last2=Gottschalk |first2=J. |last3=Seeburger |first3=J. |last4=Ziemssen |first4=E. |last5=Häfner |first5=M. |last6=Thielebein |first6=J. |last7=Einspanier |first7=A. |date=2013-08-01 |title=Characterization of the ovarian cycle in the two-toed sloths (Choloepus didactylus): An innovative, reliable, and noninvasive method using fecal hormone analyses |url=https://www.sciencedirect.com/science/article/pii/S0093691X13001453 |journal=Theriogenology |language=en |volume=80 |issue=3 |pages=275–283 |doi=10.1016/j.theriogenology.2013.04.007 |pmid=23743067 |issn=0093-691X}} The mother gives birth to a single young, while hanging upside down. The young are born with claws, and are weaned after about a month, although they will remain with the mother for several more months, and do not reach maturity until the age of three years, in the case of females, or four to five years, in the case of males. During natal dispersion, two-toed sloths prefer tropical forests over other types of habitat, often using riparian forest buffers to disperse. Although they also occupy shade-grown cacao plantations, they avoid open pastures.{{Cite journal|last1=Garcés-Restrepo|first1=Mario F.|last2=Pauli|first2=Jonathan N.|last3=Peery|first3=M. Zachariah|date=2018|title=Natal dispersal of tree sloths in a human-dominated landscape: Implications for tropical biodiversity conservation|journal=Journal of Applied Ecology|language=en|volume=55|issue=5|pages=2253–2262|doi=10.1111/1365-2664.13138|issn=1365-2664|doi-access=free|bibcode=2018JApEc..55.2253G }}

They eat primarily leaves, but also shoots, fruits, nuts, berries, bark, some native flowers, and even some small vertebrates.{{cite web | last = Myers | first = Phil | title = Family Megalonychidae: two-toed sloths | work = Animal Diversity Web | publisher = University of Michigan | year = 2001 | url = http://animaldiversity.ummz.umich.edu/site/accounts/information/Megalonychidae.html | access-date = 2009-09-14}} In addition, when they cannot find food, they have been known to eat the algae that grow on their fur for nutrients.Nowak, Ronald M. Walkers (1999) Mammals of the World. Sixth Edition. Vol. 1. Baltimore and London: The Johns Hopkins University Press. pp. 149–150. Print. They have also been observed using mineral licks.{{Cite journal |last1=Gómez-Hoyos |first1=Diego A. |last2=González-Maya |first2=José F. |last3=Pacheco |first3=Jesús |last4=Seisdedos-Vergara |first4=Seisdedos-Vergara |last5=Barrio-Amorós |first5=César L. |last6=Ceballos |first6=Gerardo |date=December 2017 |title=Mineral-Lick Use By Choloepus hoffmanni (Pilosa: Megalonychidae) At Las Cruces Biological Station, Coto Brus, Costa Rica |url=http://www.bioone.org/doi/10.1894/0038-4909-62.4.278 |journal=The Southwestern Naturalist |language=en |volume=62 |issue=4 |pages=278–280 |doi=10.1894/0038-4909-62.4.278 |bibcode=2017SWNat..62..278G |s2cid=92499258 |issn=0038-4909}}{{Cite journal |last1=Blake |first1=John G. |last2=Mosquera |first2=Diego |last3=Guerra |first3=Jaime |last4=Loiselle |first4=Bette A. |last5=Romo |first5=David |last6=Swing |first6=Kelly |date=June 2011 |title=Mineral Licks as Diversity Hotspots in Lowland Forest of Eastern Ecuador |journal=Diversity |language=en |volume=3 |issue=2 |pages=217–234 |doi=10.3390/d3020217 |issn=1424-2818 |doi-access=free |bibcode=2011Diver...3..217B }} They have large, four-chambered stomachs, which help to ferment the large amount of plant matter they eat.{{Citation|last1=Voirin|first1=Bryson|title=Why do Sloths Poop on the Ground?|date=2013|work=Treetops at Risk: Challenges of Global Canopy Ecology and Conservation|pages=195–199|editor-last=Lowman|editor-first=Margaret|publisher=Springer|language=en|doi=10.1007/978-1-4614-7161-5_19|isbn=978-1-4614-7161-5|last2=Kays|first2=Roland|last3=Wikelski|first3=Martin|last4=Lowman|first4=Margaret|editor2-last=Devy|editor2-first=Soubadra|editor3-last=Ganesh|editor3-first=T.}} Food can take up to a month to digest due to their slow metabolism. Depending on when in the excretion cycle a sloth is weighed, urine and feces may account for up to 30% of the animal's body weight.[https://web.archive.org/web/20090501024437/http://nationalzoo.si.edu/ConservationAndScience/SpotlightonVetMedicine/sloth.cfm Sloth Standards]. nationalzoo.si.edu (May 27, 2005) They get most of their fluids from water in the leaves that they eat but sloths have also been observed drinking directly from rivers.{{citation needed|date=March 2023}}

Two-toed sloths have a reduced, ever growing dentition, with no incisors or true canines, which overall lacks homology with the dental formula of other mammals. Their first tooth is very canine-like in shape and is referred to as a caniniform. It is used for tearing small chunks off of their food, as well as for defense against predators.{{Cite journal |last=Naples |first=Virginia L. |date=January 1985 |title=Form and function of the masticatory musculature in the tree sloths, Bradypus and Choloepus |url=https://onlinelibrary.wiley.com/doi/10.1002/jmor.1051830104 |journal=Journal of Morphology |language=en |volume=183 |issue=1 |pages=25–50 |doi=10.1002/jmor.1051830104 |pmid=3973924 |s2cid=36168956 |issn=0362-2525}} It is separated from the other teeth, or molariforms, by a diastema. The molariforms are used specifically for grinding and are mortar and pestle-like in appearance and function. Thus, they can grind food for easier digestibility, which takes the majority of their energy. The dental formula of two-toed sloths is: {{DentalFormula|upper=4|lower=5}} (unau)

Two-toed sloths are unusual among mammals in possessing as few as five cervical vertebrae, which may be due to mutations in the homeotic genes.{{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|work=May 6th 2011|publisher=Science Daily|access-date=25 July 2013}} All other mammals have seven cervical vertebrae,{{cite journal |pmid=10327647 |author=Frietson Galis |year=1999 |title=Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes and Cancer |journal=Journal of Experimental Zoology |url=http://wwworm.biology.uh.edu/evodevo/lecture11/galis99.pdf |volume=285 |issue=1 |pages=19–26 |doi=10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z |bibcode=1999JEZ...285...19G |url-status=dead |archive-url=https://web.archive.org/web/20041110200159/http://wwworm.biology.uh.edu/evodevo/lecture11/galis99.pdf |archive-date=10 November 2004 |df=dmy-all }} other than the three-toed sloth and the manatee.

Two-toed sloths generally have similar musculature to that of other mammals. This includes their zygomaticus muscles, their superficial masseter, their deep masseter, and their medial and lateral pterygoids. Additionally, a specific section of their anterior temporalis is arranged vertically, to allow them to sharpen their caniniform teeth. They tend to have stronger flexor muscles in their fore- and hindlimbs, as well as their shoulders.

{{NoteFoot}}

{{Reflist|30em}}

• {{aut|Linnaeus}} (1758): Systema naturae perregna tria naturae, secundum classes, ordines, genera, species cum characteribus, differentiis, syonymis, locis. Laurentii : Salvi, 824 pp.

{{Wikispecies|Choloepus}}

{{Commons|Choloepus}}

• [https://web.archive.org/web/20071018031210/http://animals.nationalgeographic.com/animals/mammals/two-toed-sloth.html National Geographic: Two-toed sloth profile]
• [http://www.bristolzoo.org.uk/learning/animals/mammals/two-toed-sloth Bristol Zoo: Two-toed sloth]
• [http://nationalzoo.si.edu/Animals/SmallMammals/fact-sloth.cfm National Zoo: Two-toed sloth] {{Webarchive|url=https://web.archive.org/web/20090511155228/http://nationalzoo.si.edu/Animals/SmallMammals/fact-sloth.cfm |date=11 May 2009 }}
• [http://www.americazoo.com/goto/index/mammals/126.htm America Zoo: Two-toed sloth]
• [http://animaldiversity.ummz.umich.edu/site/accounts/information/Megalonychidae.html Animal Diversity: Family Megalonychidae]

{{Pilosa}}

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

{{Taxonbar|from1=Q511079|from2=Q108908082}}

{{Authority control}}

Category:Sloths

Category:Mammals of Colombia

Category:Taxa named by Johann Karl Wilhelm Illiger