The pale-throated sloth (Bradypus tridactylus), occasionally known as the ai (), is a species of three-toed sloth that inhabits tropical rainforests in northern South America.
It is similar in appearance to, and often confused with, the brown-throated sloth, which has a much wider distribution. Genetic evidence has been interpreted to suggest the two species diverged only around 400,000 years ago, although the most recent evidence indicates the split was closer to 6 million years.
Description
thumb|left|Skull
The pale-throated sloth has a rounded head with a blunt nose and small external ears. Its limbs are long and relatively weak, with the arms nearly twice the length of the hindlimbs. Both the hands and feet have three digits, each equipped with long, arched claws, the middle claw being the largest and strongest.[citation needed]
Adult males measure 45 to 55 centimetres (18 to 22 in) in head-body length, with a short tail of 4 to 6 centimetres (1.6 to 2.4 in), and weigh between 3.2 and 6 kilograms (7.1 to 13.2 lb). Females are generally larger, ranging from 50 to 75 centimetres (20 to 30 in) in length and weighing 3.8 to 6.5 kilograms (8.4 to 14.3 lb).[1]
The body is covered with coarse guard hairs up to long, with a finer undercoat. Green algae live mutualistically between the microscopic scales on the surface of the guard hairs, giving the sloth a somewhat greenish appearance that serves as camouflage. Adults are blackish-grey over most of the body, with darker patches distributed over the backs, shoulders, and hips. Males have a bright yellow or orange patch on the back, divided by a central black stripe. Pale-throated sloths are difficult to distinguish from the closely related brown-throated sloth, but, as their name implies, they have a pale yellow patch on the throat.
The eyes are large and forward facing for binocular vision, with round pupils. Unusually, they appear to lack any cone cells in the retina, suggesting that the sloth is unable to see color. Despite its apparently small ears, the pale-throated sloth has excellent hearing; it has also been reported to have a good sense of smell. herbivorous animals that spend almost their entire lives in trees. Depending on habitat, population densities of anything from have been reported.
The young are born already fully furred, and with open eyes. The young animal clings to the mother's underside for the first month of life, by which time it has reached a weight of around . They begin to take solid food at three weeks, and are fully weaned some time after the first month. The young initially have soft greyish-brown fur, which darkens and becomes rougher as they age.