Three-toed sloth
The three-toed sloths (genus Bradypus) are a group of arboreal xenarthran mammals in the family Bradypodidae and order Pilosa, distinguished by their extremely slow movements, specialized limb structure with three claws on each forelimb, and long, coarse fur that often harbors symbiotic algae for camouflage.[1] Native exclusively to the tropical rainforests of Central and South America, they are strictly canopy-dwellers, spending nearly their entire lives suspended upside down from branches, descending to the ground only once every six to eight days to defecate.[2] There are five extant species in the genus: the widespread brown-throated sloth (B. variegatus), the northern maned sloth (B. torquatus), the southern maned sloth (B. crinitus), the pale-throated sloth (B. tridactylus), and the critically endangered pygmy three-toed sloth (B. pygmaeus).[1][3] These sloths are folivores, deriving over 99% of their diet from leaves—primarily tender young ones from at least 51 plant species—supplemented occasionally by fruits, twigs, and flowers, which they consume slowly due to a multi-chambered stomach and low metabolic rate that can take up to a month to fully digest a single meal.[1] Adults typically weigh 2.25–6.2 kg (5–13.7 lb) and measure about 50–60 cm (20–24 in) in body length, with females generally larger than males; their shaggy pelage, which grows in the opposite direction on the face and limbs to facilitate upside-down living, provides insulation and hosts a unique ecosystem of insects and microorganisms.[2] Behaviorally solitary and largely diurnal or crepuscular without a strict circadian rhythm, they move at maximum speeds of 0.24 km/h (0.15 mph) on land but are surprisingly adept swimmers, using their long arms to propel through water at up to 1.03 km/h (0.64 mph).[4] Despite their unhurried pace aiding energy conservation in nutrient-poor habitats, three-toed sloths face significant threats from habitat destruction due to deforestation, fragmentation of rainforest canopies, and the illegal pet trade, with some species like the pygmy three-toed sloth classified as critically endangered by the IUCN.[1] Their ecological role includes seed dispersal and nutrient cycling in forest ecosystems, as undigested seeds pass through their slow digestive systems intact, promoting tree regeneration.[2] Conservation efforts focus on protecting contiguous rainforest habitats and rehabilitating rescued individuals, underscoring the need to address human encroachment in their range across countries like Brazil, Costa Rica, and Panama.[1]Taxonomy and evolution
Extant species
The genus Bradypus comprises four to five extant species of three-toed sloths, all endemic to Central and northern South America, depending on taxonomic authority. These species are distinguished primarily through morphological traits such as fur coloration, body size, and cranial features, as well as genetic markers from mitochondrial DNA analyses that reveal deep phylogenetic divergences. While traditional classifications recognize four species, recent taxonomic revisions propose a fifth based on molecular evidence. Recent taxonomic revisions have refined the classification within Bradypus, notably the 2022 recognition of the southern maned three-toed sloth (Bradypus crinitus) as a distinct species from the northern maned three-toed sloth (B. torquatus), based on molecular studies demonstrating over 4 million years of divergence and subtle cranial differences, such as a more rounded head shape in B. crinitus. This split is recognized in scientific literature but B. crinitus remains Not Evaluated by the IUCN as of 2025, while B. torquatus was upgraded from Vulnerable to Endangered in the 2025 IUCN assessment. Earlier revisions include the description of the pygmy three-toed sloth (B. pygmaeus) in 2001, confirmed by genetic data showing it is not a dwarf form of B. variegatus but a distinct lineage.[5][6][7][8] The following table summarizes the extant species, their key distinguishing features, and primary distributions:| Scientific Name | Common Name | Key Distinctions | Distribution |
|---|---|---|---|
| Bradypus variegatus | Brown-throated three-toed sloth | Light brown fur with a distinctive tan-to-yellow throat patch; body length 42–63 cm; three genetic haplogroups in Amazonian populations indicating subtle phylogeographic variation.[7] | Widespread in Central America (Honduras to Panama) and northern South America (Colombia, Venezuela, Peru, Bolivia, northern Brazil). |
| Bradypus tridactylus | Pale-throated three-toed sloth | Pale yellowish fur with a white-to-pale throat; longer muzzle than B. variegatus; mitochondrial divergence of ~7–9 million years from other Bradypus.[7] | Northern South America, including the Guianas, northern Brazil, southern Venezuela, and eastern Colombia, primarily in Amazonian rainforests. |
| Bradypus torquatus | Northern maned three-toed sloth | Dark brown fur with long, mane-like hairs on shoulders and neck forming a collar; lacks a mid-dorsal light patch; genetic divergence suggesting separate genus status in some analyses; IUCN status Endangered as of 2025.[7][8] | Atlantic Forest of northeastern Brazil (Bahia to Rio de Janeiro states). |
| Bradypus pygmaeus | Pygmy three-toed sloth | Smallest species, with body length up to 30 cm and weight ~300–400 g; shorter, denser fur than B. variegatus; distinct mitochondrial lineage diverging ~7 million years ago.[7] | Endemic to Isla Escudo de Veraguas, off the northern coast of Panama. |
| Bradypus crinitus | Southern maned three-toed sloth | Similar to B. torquatus with mane-like fur, but distinguished by rounder cranial shape and lower genetic diversity; separated by ancient climatic barriers; IUCN status Not Evaluated as of 2025.[5][6][9] | Atlantic Forest of southeastern Brazil (São Paulo to Santa Catarina states), south of B. torquatus range.[6] |