Two-toed sloth

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Two-toed sloths [1]
2 toed sloth.jpg
Hoffmann's two-toed sloth (C. hoffmanni)
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Pilosa
Superfamily: Mylodontoidea
Family: Choloepodidae
Gray, 1871 [2]
Genus: Choloepus
Illiger, 1811 [1]
Type species
Bradypus didactylus
Linnaeus, 1758
Species
Two toed sloth range species.jpg

Choloepus is a genus of xenarthran mammals from Central and South America within the monotypic family Choloepodidae, consisting of two-toed sloths, [3] sometimes also called two-fingered sloths. [4] The two species of Choloepus (which means "lame foot" [5] ), Linnaeus's two-toed sloth (Choloepus didactylus) and Hoffmann's two-toed sloth (Choloepus hoffmanni), were formerly believed on the basis of morphological studies to be the only surviving members of the sloth family Megalonychidae, [6] but have now been shown by molecular results to be closest to extinct ground sloths of the family Mylodontidae. [4] [3]

Contents

Extant species

Genus Choloepus Illiger, 1811 – two species
Common nameScientific name and subspeciesRangeSize and ecologyIUCN status and estimated population
Linnaeus's two-toed sloth

Cholepus didactylus - Flickr - Dick Culbert.jpg

Choloepus didactylus
(Linnaeus, 1758)
Northern South America, found in Venezuela, the Guyanas, Colombia, Ecuador, Peru, and Brazil north of the Amazon River
Linne's Two-toed Sloth area.png
Size:

Habitat:

Diet:
 LC 


Hoffmann's two-toed sloth

Choloepus hoffmanni (Puerto Viejo, CR) crop.jpg

Choloepus hoffmanni
Peters, 1858

Five subspecies
  • 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
Central America and northwestern South America
Hoffmann's Two-toed Sloth area.png
Size:

Habitat:

Diet:
 LC 


Evolution

A study of retrovirus and mitochondrial DNA suggests that C. didactylus and C. hoffmani diverged 6 to 7 million years ago. [7] Furthermore, based on cytochrome c oxidase subunit I sequences, a similar divergence date (c.7 million years ago) between the two populations of C. hofmanni separated by the Andes has been reported. [8] Their ancestors evolved with marine vertebrae, the three toed-sloth and the manatee are the only other mammals with similar vertebrae. [9]

Relation to the three-toed sloth

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 [10] 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. [11] 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. [12]

Much of the morphological evidence to support the hypothesis of diphyly has been based on the structure of the inner ear. [13] 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”. [12]

Recently obtained molecular data from collagen [3] and mitochondrial DNA [4] 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. [3] [4]

The following sloth family phylogenetic tree is based on collagen and mitochondrial DNA sequence data (see Fig. 4 of Presslee et al., 2019). [3]

Folivora

Characteristics

Display of two "fingers" on forelimbs and three toes on hindlimbs TwoToedSlothDetail.jpg
Display of two "fingers" on forelimbs and three toes on hindlimbs

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. [note 1]

Members of Choloepus are larger than three-toed sloths, having a body length of 58 to 70 centimetres (23 to 28 in), and weighing 4 to 8 kilograms (8.8 to 17.6 lb). Other distinguishing features include a more prominent snout, longer fur, and the absence of a tail. [14]

Behaviour

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. [15] [16] Being predominantly nocturnal, their fur, which grows greenish algae to blend in, is their main source of protection. [17] 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. [14] Two-toed sloths also differ from three-toed sloths in their climbing behavior, preferring to descend head first.

Lifecycle

Young C. hoffmanni being raised in a wildlife rescue center in the Osa Peninsula, Costa Rica Baby Choloepus hoffmanni, Costa Rica.JPG
Young C. hoffmanni being raised in a wildlife rescue center in the Osa Peninsula, 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. [18] 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. [16] 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. [19]

Feeding

They eat primarily leaves, but also shoots, fruits, nuts, berries, bark, some native flowers, and even some small vertebrates. [20] In addition, when they cannot find food, they have been known to eat the algae that grow on their fur for nutrients. [21] They have also been observed using mineral licks. [22] [23] They have large, four-chambered stomachs, which help to ferment the large amount of plant matter they eat. [24] Food can take up to a month to digest due to their slow metabolism. [14] 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. [25] 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 ]

Dentition and skeleton

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. [26] 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: 45 (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. [27] All other mammals have seven cervical vertebrae, [28] other than the three-toed sloth and the manatee.

Musculature

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. [26] They tend to have stronger flexor muscles in their fore- and hindlimbs, as well as their shoulders. [15]

Notes

  1. Given that sloths are regarded as quadrupeds, whether their forelimb digits should be described as fingers is debatable.

Related Research Articles

<span class="mw-page-title-main">Xenarthra</span> Superorder of mammals including anteaters, sloths, and armadillos

Xenarthra is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. Extinct xenarthrans include the glyptodonts, pampatheres and ground sloths. Xenarthrans originated in South America during the late Paleocene about 60 million years ago. They evolved and diversified extensively in South America during the continent's long period of isolation in the early to mid Cenozoic Era. They spread to the Antilles by the early Miocene and, starting about 3 million years ago, spread to Central and North America as part of the Great American Interchange. Nearly all of the formerly abundant megafaunal xenarthrans became extinct at the end of the Pleistocene.

<span class="mw-page-title-main">Mylodontidae</span> Extinct family of ground sloths

Mylodontidae is a family of extinct South American and North American ground sloths within the suborder Folivora of order Pilosa, living from around 23 million years ago (Mya) to 11,000 years ago. This family is most closely related to another family of extinct ground sloths, Scelidotheriidae, as well as to the extant arboreal two-toed sloths, family Choloepodidae; together these make up the superfamily Mylodontoidea. Phylogenetic analyses based on morphology uncovered the relationship between Mylodontidae and Scelidotheriidae; in fact, the latter was for a time considered a subfamily of mylodontids. However, molecular sequence comparisons were needed for the correct placement of Choloepodidae. These studies have been carried out using mitochondrial DNA sequences as well as with collagen amino acid sequences. The latter results indicate that Choloepodidae is closer to Mylodontidae than Scelidotheriidae is. The only other living sloth family, Bradypodidae, belongs to a different sloth radiation, Megatherioidea.

<span class="mw-page-title-main">Scelidotheriidae</span> Extinct family of prehistoric ground sloths

Scelidotheriidae is a family of extinct ground sloths within the order Pilosa, suborder Folivora and superfamily Mylodontoidea, related to the other extinct mylodontoid family, Mylodontidae, as well as to the living two-toed sloth family Choloepodidae. The only other extant family of the suborder Folivora is the distantly related Bradypodidae. Erected as the family Scelidotheriidae by Ameghino in 1889, the taxon was demoted to a subfamily of Mylodontidae by Gaudin in 1995. However, recent collagen sequence data indicates the group is less closely related to Mylodon and Lestodon than Choloepus is, and thus it has been elevated back to full family status by Presslee et al. (2019).

<span class="mw-page-title-main">Pale-throated sloth</span> Species of mammals related to anteaters and armadillos

The pale-throated sloth, occasionally known as the ai, is a species of three-toed sloth that inhabits tropical rainforests in northern South America.

<span class="mw-page-title-main">Silky anteater</span> Species of mammals related to sloths and armadillos

The silky anteater, also known as the pygmy anteater, has traditionally been considered a single species of anteater, Cyclopes didactylus, in the genus Cyclopes, the only living genus in the family Cyclopedidae. Found in southern Mexico, and Central and South America, it is the smallest of all known anteaters. It has nocturnal habits and appears to be completely arboreal; its hind feet are highly modified for climbing.

<span class="mw-page-title-main">Brown-throated sloth</span> Species of New World mammals related to anteaters and armadillos

The brown-throated sloth is a species of three-toed sloth found in the Neotropical realm of Central and South America.

<span class="mw-page-title-main">Hoffmann's two-toed sloth</span> Species of mammals related to anteaters and armadillos

The Hoffmann's two-toed sloth, also known as the northern two-toed sloth, is a species of sloth from Central and South America. It is a solitary, largely nocturnal and arboreal animal, found in mature and secondary rainforests and deciduous forests. The common name commemorates the German naturalist Karl Hoffmann.

<span class="mw-page-title-main">Linnaeus's two-toed sloth</span> Species of mammals related to anteaters and armadillos

Linnaeus's two-toed sloth, also known as the southern two-toed sloth, unau, or Linne's two-toed sloth is a species of sloth from South America, found in Venezuela, Suriname, Guyana, French Guiana, Colombia, Ecuador, Peru, and Brazil north of the Amazon River. There is now evidence suggesting the species' range expands into Bolivia. It's the largest extant sloth species.

<span class="mw-page-title-main">Pilosa</span> Order of mammals

The order Pilosa is a clade of xenarthran placental mammals, native to the Americas. It includes anteaters and sloths. The name comes from the Latin word for "hairy".

<span class="mw-page-title-main">Megalonychidae</span> Extinct family of sloths

Megalonychidae is an extinct family of sloths including the extinct Megalonyx. Megalonychids first appeared in the early Oligocene, about 35 million years (Ma) ago, in southern Argentina (Patagonia). There is, however, one possible find dating to the Eocene, about 40 Ma ago, on Seymour Island in Antarctica. They first reached North America by island-hopping across the Central American Seaway, about 9 million years ago, prior to formation of the Isthmus of Panama about 2.7 million years ago. Some megalonychid lineages increased in size as time passed. The first species of these were small and may have been partly tree-dwelling, whereas the Pliocene species were already approximately half the size of the huge Late Pleistocene Megalonyx jeffersonii from the last ice age.

<span class="mw-page-title-main">Three-toed sloth</span> Genus of mammals

The three-toed or three-fingered sloths are arboreal neotropical mammals. They are the only members of the genus Bradypus and the family Bradypodidae. The five living species of three-toed sloths are the brown-throated sloth, the maned sloth, the pale-throated sloth, the southern maned sloth, and the pygmy three-toed sloth. In complete contrast to past morphological studies, which tended to place Bradypus as the sister group to all other folivorans, molecular studies place them nested within the sloth superfamily Megatherioidea, making them the only surviving members of that radiation.

<span class="mw-page-title-main">Sloth</span> Group of tree dwelling mammals noted for slowness

Sloths are a Neotropical group of xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their lives hanging upside down in the trees of the tropical rainforests of South America and Central America. Sloths are considered to be most closely related to anteaters, together making up the xenarthran order Pilosa.

<span class="mw-page-title-main">Pygmy three-toed sloth</span> Species of mammals related to anteaters and armadillos

The pygmy three-toed sloth, also known as the monk sloth or dwarf sloth, is a species of sloth in the family Bradypodidae. The species is endemic to Isla Escudo de Veraguas, a small island off the Caribbean coast of Panama. The species was first described by Robert P. Anderson of the University of Kansas and 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 48 and 53 centimetres, and the body mass ranges from 2.5 to 3.5 kg.

The mammalian order Pilosa, which includes the sloths and anteaters, includes various species from the Caribbean region. Many species of sloths are known from the Greater Antilles, all of which became extinct over the last millennia, but some sloths and anteaters survive on islands closer to the mainland.

<span class="mw-page-title-main">Arthropods associated with sloths</span>

A large number of arthropods are associated with sloths. These include biting and blood-sucking flies such as mosquitoes and sandflies, triatomine bugs, lice, ticks and mites. The sloth’s fur forms a micro-ecozone inhabited by green algae and hundreds of insects. Sloths have a highly specific community of commensal beetles, mites and moths.

<i>Ahytherium</i> Extinct genus of sloths

Ahytherium is an extinct genus of megalonychid sloth that lived during the Pleistocene of what is now Brazil. It contains a single species, A. aureum.

<i>Proeremotherium</i> Extinct genus of mammals

Proeremotherium is an extinct genus of megatheriine ground sloths in the family Megatheriidae. It lived during the Late Miocene and Early Pliocene of what is now Venezuela. So far, two largely complete skulls have been recovered in the Falcón Basin in Venezuela. The finds identify the animals as medium-sized representatives of the Megatheriidae. In the cranial anatomy, Proeremotherium resembles the later and giant Eremotherium. It is therefore assumed that the two ground sloths are directly related to each other.

Lakukullus is an extinct genus of nothrotheriid ground sloths that lived during the Middle Miocene around 13.8 to 11.8 million years ago of what is now Bolivia.

<i>Ortotherium</i> Extinct genus of ground sloth

Ortotherium is a genus of megalonychid ground sloth from the Late Miocene Ituzaingó Formation of Entre Rios Province, Argentina. Although many species were described, the only valid species of the genus is Ortotherium laticurvatum, with many species being junior synonyms. Ortotherium is known from very fragmentary material, all of which is material from the mandible and teeth. The holotype of O. laticurvatum consists of an incomplete left dentary that had been unearthed from a series of sediments known as ‘Conglomerado osifero’ in Paraná, Argentina. Argentina paleontologist Florentino Ameghino named the species in 1885, though he would go on to name four more, invalid, species of the genus. One species however, O. brevirostrum, has been reclassified as Mesopotamocnus.

References

  1. 1 2 Gardner, A. L. (2005). "Genus Choloepus". In Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 101–102. ISBN   978-0-8018-8221-0. OCLC   62265494.
  2. Anderson, S. (1997). "Mammals of Bolivia, Taxonomy and Distribution". Bulletin of the AMNH (231): 168.
  3. 1 2 3 4 5 Presslee, S.; Slater, G. J.; Pujos, F.; Forasiepi, A. M.; Fischer, R.; Molloy, K.; et al. (2019). "Palaeoproteomics resolves sloth relationships" (PDF). Nature Ecology & Evolution. 3 (7): 1121–1130. Bibcode:2019NatEE...3.1121P. doi:10.1038/s41559-019-0909-z. PMID   31171860. S2CID   174813630. Archived (PDF) from the original on 12 September 2020. Retrieved 18 September 2020.
  4. 1 2 3 4 Delsuc, F.; Kuch, M.; Gibb, G. C.; Karpinski, E.; Hackenberger, D.; Szpak, P.; Martínez, J. G.; Mead, J. I.; McDonald, H. G.; MacPhee, R.D.E.; Billet, G.; Hautier, L.; Poinar, H. N. (2019). "Ancient Mitogenomes Reveal the Evolutionary History and Biogeography of Sloths". Current Biology. 29 (12): 2031–2042.e6. Bibcode:2019CBio...29E2031D. doi: 10.1016/j.cub.2019.05.043 . hdl: 11336/136908 . PMID   31178321.
  5. "Sloth-World.org". Archived from the original on 2 February 2009.
  6. Myers, Phil (2001). "Family Megalonychidae: two-toed sloths". Animal Diversity Web. University of Michigan. Archived from the original on 11 March 2017. Retrieved 11 March 2017.
  7. Slater, G. J.; Cui, P.; Forasiepi, A. M.; Lenz, D.; Tsangaras, K.; Voirin, B.; de Moraes-Barros, N.; MacPhee, R. D. E.; Greenwood, A. D. (14 February 2016). "Evolutionary Relationships among Extinct and Extant Sloths: The Evidence of Mitogenomes and Retroviruses". Genome Biology and Evolution. 8 (3): 607–621. doi:10.1093/gbe/evw023. PMC   4824031 . PMID   26878870.
  8. Moraes-Barros, N.; Arteaga, M. C. (1 June 2015). "Genetic diversity in Xenarthra and its relevance to patterns of neotropical biodiversity". Journal of Mammalogy. 96 (4): 690–702. doi: 10.1093/jmammal/gyv077 .
  9. Muizon, C. de; McDonald, H. G. (May 1995). "An aquatic sloth from the Pliocene of Peru". Nature. 375 (6528): 224–227. Bibcode:1995Natur.375..224M. doi:10.1038/375224a0. ISSN   1476-4687. S2CID   4369283.
  10. Hoss, Matthias; Dilling, Amrei; Currant, Andrew; Paabo, Svante (9 January 1996). "Molecular phylogeny of the extinct ground sloth Mylodon darwinii". Proceedings of the National Academy of Sciences . 93 (1): 181–185. Bibcode:1996PNAS...93..181H. doi: 10.1073/pnas.93.1.181 . PMC   40202 . PMID   8552600.
  11. White, J.L.; MacPhee, R.D.E. (2001). "The sloths of the West Indies: a systematic and phylogenetic review". In Woods, C.A.; Sergile, F.E. (eds.). Biogeography of the West Indies: Patterns and Perspectives. Boca Raton, London, New York, and Washington, D.C.: CRC Press. pp. 201–235. doi:10.1201/9781420039481-14. ISBN   978-0-8493-2001-9.
  12. 1 2 Gaudin, Timothy (2004). "Phylogenetic Relationships among Sloths (Mammalia, Xenarthra, Tardigrada): The Craniodental Evidence". Zoological Journal of the Linnean Society. 140 (2): 255–305. doi: 10.1111/j.1096-3642.2003.00100.x .
  13. Raj Pant, Sara; Goswami, Anjali; Finarelli, John A (2014). "Complex body size trends in the evolution of sloths (Xenarthra: Pilosa)". BMC Evolutionary Biology. 14 (1): 184. Bibcode:2014BMCEE..14..184R. doi: 10.1186/s12862-014-0184-1 . PMC   4243956 . PMID   25319928.
  14. 1 2 3 Dickman, Christopher R. (1984). Macdonald, D. (ed.). The Encyclopedia of Mammals . New York: Facts on File. pp.  776–779. ISBN   0-87196-871-1.
  15. 1 2 Granatosky, Michael C.; Karantanis, Nikolaos E.; Rychlik, Leszek; Youlatos, Dionisios (December 2018). "A suspensory way of life: Integrating locomotion, postures, limb movements, and forces in two-toed sloths Choloepus didactylus (Megalonychidae, Folivora, Pilosa): GRANATOSKY et al". Journal of Experimental Zoology Part A: Ecological and Integrative Physiology. 329 (10): 570–588. doi:10.1002/jez.2221. PMID   30129260. S2CID   52050040.
  16. 1 2 Gilmore, D. P.; Da-Costa, C. P.; Duarte, D. P. F. (February 2000). "An update on the physiology of two- and three-toed sloths". Brazilian Journal of Medical and Biological Research. 33 (2): 129–146. doi: 10.1590/S0100-879X2000000200001 . ISSN   0100-879X. PMID   10657054.
  17. "sloth." Encyclopædia Britannica.
  18. Troll, S.; Gottschalk, J.; Seeburger, J.; Ziemssen, E.; Häfner, M.; Thielebein, J.; Einspanier, A. (1 August 2013). "Characterization of the ovarian cycle in the two-toed sloths (Choloepus didactylus): An innovative, reliable, and noninvasive method using fecal hormone analyses". Theriogenology. 80 (3): 275–283. doi:10.1016/j.theriogenology.2013.04.007. ISSN   0093-691X. PMID   23743067.
  19. Garcés-Restrepo, Mario F.; Pauli, Jonathan N.; Peery, M. Zachariah (2018). "Natal dispersal of tree sloths in a human-dominated landscape: Implications for tropical biodiversity conservation". Journal of Applied Ecology. 55 (5): 2253–2262. Bibcode:2018JApEc..55.2253G. doi: 10.1111/1365-2664.13138 . ISSN   1365-2664.
  20. Myers, Phil (2001). "Family Megalonychidae: two-toed sloths". Animal Diversity Web. University of Michigan . Retrieved 14 September 2009.
  21. 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.
  22. Gómez-Hoyos, Diego A.; González-Maya, José F.; Pacheco, Jesús; Seisdedos-Vergara, Seisdedos-Vergara; Barrio-Amorós, César L.; Ceballos, Gerardo (December 2017). "Mineral-Lick Use By Choloepus hoffmanni (Pilosa: Megalonychidae) At Las Cruces Biological Station, Coto Brus, Costa Rica". The Southwestern Naturalist. 62 (4): 278–280. doi:10.1894/0038-4909-62.4.278. ISSN   0038-4909. S2CID   92499258.
  23. Blake, John G.; Mosquera, Diego; Guerra, Jaime; Loiselle, Bette A.; Romo, David; Swing, Kelly (June 2011). "Mineral Licks as Diversity Hotspots in Lowland Forest of Eastern Ecuador". Diversity. 3 (2): 217–234. doi: 10.3390/d3020217 . ISSN   1424-2818.
  24. Voirin, Bryson; Kays, Roland; Wikelski, Martin; Lowman, Margaret (2013), Lowman, Margaret; Devy, Soubadra; Ganesh, T. (eds.), "Why do Sloths Poop on the Ground?", Treetops at Risk: Challenges of Global Canopy Ecology and Conservation, Springer, pp. 195–199, doi:10.1007/978-1-4614-7161-5_19, ISBN   978-1-4614-7161-5
  25. Sloth Standards. nationalzoo.si.edu (May 27, 2005)
  26. 1 2 Naples, Virginia L. (January 1985). "Form and function of the masticatory musculature in the tree sloths, Bradypus and Choloepus". Journal of Morphology. 183 (1): 25–50. doi:10.1002/jmor.1051830104. ISSN   0362-2525. PMID   3973924. S2CID   36168956.
  27. "Sticking Their Necks out for Evolution: Why Sloths and Manatees Have Unusually Long (or Short) Necks". May 6th 2011. Science Daily. Retrieved 25 July 2013.
  28. Frietson Galis (1999). "Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes and Cancer" (PDF). Journal of Experimental Zoology. 285 (1): 19–26. Bibcode:1999JEZ...285...19G. doi:10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z. PMID   10327647. Archived from the original (PDF) on 10 November 2004.