Sloth

Sloths are a group of Neotropical xenarthran mammals from the Americas, including Central and South America. They form the suborder Folivora. This group includes the living arboreal tree sloths and the extinct ground sloths. Tree sloths are famous for their slow movement. They spend most of their lives hanging upside down in the trees of the tropical rainforests of South America and Central America. Sloths are most closely related to anteaters, and together they make up the order Pilosa.

There are seven living sloth species in two genera: Bradypus (three-toed sloths) and Choloepus (two-toed sloths). The names are traditional, but all sloths have three toes on each back leg. Two-toed sloths have only two digits on each front leg. The two groups come from different families. They are thought to have developed similar body shapes through parallel evolution from ancestors that lived on the ground. Many ground sloths lived in North and South America during the Pleistocene Epoch. Some were as large as elephants, like Megatherium. They died out during the Quaternary extinction event around 12,000 years ago, along with most large animals across the Americas. This happened around the time humans arrived, but climate change has also been suggested as a cause. Caribbean sloths were found only in the Greater Antilles and were part of a radiation of Caribbean sloths. They also died out after people settled the islands around 6,000 years ago.

Sloths get their name from their very low metabolism and their slow, careful movements. The word sloth is related to slow and literally means "laziness." Their names in several other languages also mean "lazy" or something similar, such as German Faultier, French paresseux, Spanish perezoso, Portuguese preguiça, Romanian leneș, and Finnish laiskiainen.

Their slowness helps them live on a low-energy diet of leaves. It also helps them avoid being noticed by hawks and cats that hunt by sight. Sloths are almost helpless on the ground, but they can swim. Their shaggy coat has grooved hair that hosts green algae. These algae camouflage the animal in the trees and provide it with nutrients. The algae also feed sloth moths, and some species of these moths live only on sloths.

This article is about the Central and South American mammal. For the cardinal sin, see [Sloth (deadly sin)](/wiki/Sloth_(deadly_sin). For other uses, see [Sloth (disambiguation)](/wiki/Sloth_(disambiguation).

Taxonomy and evolution

See also: List of pilosans

Sloths belong to Xenarthra, a group of placental mammals. Scientists think this group began in South America around 60 million years ago. Anteaters and armadillos are also in this group. Sloths belong to the suborder Folivora, whose name means "leaf eater." They are part of the order Pilosa, which means "hairy." Most Folivora families have died out. Only two families still have living species: the three-toed sloths and the two-toed sloths.

The two living sloth groups share a common ancestor that lived about 28 million years ago. They look alike in some ways even though they are not closely related. This happens through convergent evolution, when unrelated animals develop similar traits. Ancient sloths lived mostly on land. Some, such as Megatherium, were about as big as elephants. Sloths began in South America and later spread to some Caribbean islands and North America. Ground sloths disappeared from North and South America soon after people arrived about 11,000 years ago. Human hunting may have played a part. Climate change at the end of the last ice age may also have had an effect.

Biology

Sloths are mammals with fewer neck bones than most. Most mammals have seven cervical vertebrae, but two-toed sloths have five to seven, and three-toed sloths have eight or nine. Sloths can see colours and can smell and touch things well. They see and hear poorly, so they find food mainly by smell and touch. When they rest, they use very little energy. Their body temperature changes with the weather around them, because they are heterothermic. It can get cold enough to cause torpor. Sloths hang from branches with their strong arms and long, curved claws. They move very slowly, about 4 metres (13 feet) per minute, but they are good swimmers. Their fur grows in the opposite direction from most mammals' fur. Algae live in it, and this can help hide them from predators such as jaguars, ocelots, and harpy eagles. Sloths spend most of their time not moving.

Sloths usually live alone and rarely meet other sloths, except during the breeding season. About once every eight days, they climb down to the ground to go to the toilet. Scientists have long wondered why. Two-toed sloths are omnivorous, so they eat insects, carrion, fruits, leaves, and small lizards. Three-toed sloths are herbivorous and eat leaves from only a few kinds of trees. Leaves are hard to digest, so they have large stomachs. Symbiotic bacteria live there and help break down the leaves. Digestion can take a month or more. Baby sloths learn what to eat by licking their mother's lips. All sloths eat the leaves of Cecropia. Three-toed sloths usually give birth to one baby after about six months of gestation. Two-toed sloths take about 12 months. Males and females look very much alike. In human care, sloths usually live about 16 years. One sloth at the Smithsonian Institution's National Zoo lived to 49.

Distribution

Sloths live only in the warm rainforests of Central and South America, and they do very well there. On Barro Colorado Island in Panama, sloths are thought to make up 70 percent of the biomass of tree-living mammals.

Four of the six living species are currently rated "least concern," which means they are not in much danger. The maned three-toed sloth (Bradypus torquatus) lives in Brazil's Atlantic Forest, which is getting smaller, and it is classified as "vulnerable." The pygmy three-toed sloth (B. pygmaeus), which lives on an island, is critically endangered. Sloths have a low metabolism, so they can only live in warm places. To keep their body temperature right, they act a bit like cold-blooded animals, such as by sunning themselves.

Human relations

Many sloths in Costa Rica die after touching electrical lines or because of poachers. Their claws also help them stay safe from people who hunt them. When a sloth hangs upside-down in a tree, its claws hold it tightly, so it usually does not fall.

Sometimes sloths are taken from the wild and sold as pets. However, they are generally very poor pets because of their special way of life.