Sloths are mammals classified in the families Megalonychidae (two-toed sloths) and Bradypodidae (three-toed sloths), including six extant species. They are named after the capital sin of sloth because they seem slow and lazy at first glance; however, their usual idleness is due to metabolic adaptations for conserving energy. Aside from their surprising speed during emergency flights from predators, other notable traits of sloths include their strong body and their ability to host symbiotic algae on their furs.
They are classified in the order Pilosa because they are related to anteaters, which sport a similar set of specialized claws. Extinct sloth species include many megafaunal ground sloths, some of which attained the size of elephants, as well as a few species of marine sloths. Extant sloths are medium-sized arboreal (tree-dwelling) residents of the jungles of Central and South America.
Sloths make good habitats for other organisms, and a single sloth may be home to moths, beetles, cockroaches, fungi, ciliates, and algae.[2]
Sloth fur exhibits specialized functions: the outer hairs grow in a direction opposite from that of other mammals. In most mammals, hairs grow toward the extremities, but because sloths spend so much time with their legs above their bodies, their hairs grow away from the extremities to provide protection from the elements while the sloth hangs upside down. In most conditions, the fur hosts two species of symbiotic algae, which provide camouflage.[10][11] Because of the algae, sloth fur is a small ecosystem of its own, hosting many species of non-parasitic insects. Sloths have short, flat heads, big eyes; short snouts, long legs, and tiny ears. Some species have stubby tails (6–7 cm long). Altogether, sloths' bodies usually are between 50 and 60 cm long.
Sloths' claws serve as their only natural defense. A cornered sloth may swipe at its attackers in an effort to scare them away or wound them. Despite sloths' apparent defenselessness, predators do not pose special problems: sloths blend in with the trees and, moving only slowly, do not attract attention. Only during their infrequent visits to ground level do they become vulnerable. The main predators of sloths are the jaguar, the harpy eagle, and humans. The majority of recorded sloth deaths in Costa Rica are due to contact with electrical lines and poachers. Their claws also provide a further unexpected deterrent to human hunters; when hanging upside-down in a tree, they are held in place by the claws themselves and often do not fall down even if shot from below.
Despite their adaptation to living in trees, sloths (like many other rainforest animals) make competent swimmers. This is likely to have been true of the extinct ground sloths, as well, as evidenced by the fact that megalonychid sloths were able to colonise the Antilles by the Oligocene, and that the megalonychid Pliometanastes and the mylodontid Thinobadistes were able to colonise North America about 9 million years ago, well before the existence of the Isthmus of Panama. Additionally, the nothrotheriid Thalassocnus of the west coast of South America became adapted to a semiaquatic marine lifestyle.
https://en.wikipedia.org/wiki/Sloth