Pale-throated Three-toed Sloth
Encyclopedia
The Pale-throated sloth (Bradypus tridactylus) is a species of three-toed sloth
that inhabits tropical rainforest
s 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 suggests that the two species diverged only around 400,000 years ago.
The body is covered with coarse guard hair
s up to 10 centimetres (3.9 in) 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, 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 cell
s 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
.
. Males have no discrete prostate gland, no scrotum
, and only rudimentary seminal vesicle
s.
The mouth is lined by a black colored mucosa, although the large and heavy tongue is pink. The palate is wrinkled in texture, and the tongue is lined with numerous grooves, apparently adaptations to the sloth's diet. Like other three-toed sloths, it has just five teeth on each side of the upper jaw, and four on each side of the lower jaw; these are all simple and rounded in shape, with the front teeth in the upper jaw being much smaller than the others. The esophagus
is short, but the stomach is large and complex, and there is also a large diverticulum
in the cecum
.
, Suriname
, French Guiana
, western Venezuela
and Colombia
, and Brazil
north of the Amazon River
. There are no recognised subspecies.
, Ceiba
, Elizabetha
, and Hevea
. Known predators include jaguar
s, margay
s, harpy eagles, and anaconda
s.
The Pale-throated sloth can hang so securely with its hooklike claws that it even falls asleep in this position. It may even stay suspended in the trees for some time after it dies. They have been reported to spend over eighteen hours each day asleep, and move through the tree canopy only very slowly. They periodically descend from the trees to defecate, depositing a pile of small pellets in a hole dug into the ground. Despite their arboreal lifestyle, they are effective swimmers. Their call is a bird-like whistle described as an "ai-ai" sound.
In addition to their mutualism with green algae, pale-throated sloths are also commensal with sloth moth
s, and with certain species of beetle. These insects live in the sloth's fur, and lay their eggs in its dung, on which their larvae feed.
period of about six months.
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 300 grams (10.6 oz). 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. They reach sexual maturity at around three years.
Three-toed sloth
The three-toed sloths are tree-living mammals from South and Central America. They are the only members of the genus Bradypus and the family Bradypodidae. There are four living species of three-toed sloths...
that inhabits tropical rainforest
Tropical rainforest
A tropical rainforest is an ecosystem type that occurs roughly within the latitudes 28 degrees north or south of the equator . This ecosystem experiences high average temperatures and a significant amount of rainfall...
s 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 suggests that the two species diverged only around 400,000 years ago.
Description
Pale-throated sloths have a rounded head with a blunt nose and small external ears. The limbs are long and weak, with the arms being nearly twice the length of the hindlimbs. The hands and feet each have three digits, armed with long, arched claws, with the middle claw being the largest and most powerful. Males are 45 to 55 cm (17.7 to 21.7 ) in head-body length, with a short, 4 to 6 cm (1.6 to 2.4 ), tail, and weigh from 3.2 to 6 kg (7.1 to 13.2 ). However, the females are noticeably larger, being from 50 to 75 cm (19.7 to 29.5 ) in length, and weighing 3.8 to 6.5 kg (8.4 to 14.3 ).The body is covered with coarse guard hair
Guard hair
Guard hairs are the longest, coarsest hairs in a mammal's coat, forming the topcoat . They taper to a point and protect the undercoat from the elements. They are often water repellent and stick out above the rest of the coat...
s up to 10 centimetres (3.9 in) long, with a finer undercoat. Green algae
Green algae
The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
live mutualistically between the microscopic scales on the surface of the guard hairs, giving the sloth a somewhat greenish appearance that serves as camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
. 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, have a pale yellow patch on the throat.
The eyes are large and forward facing for binocular vision
Binocular vision
Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
, with round pupils. Unusually, they appear to lack any cone cell
Cone cell
Cone cells, or cones, are photoreceptor cells in the retina of the eye that are responsible for color vision; they function best in relatively bright light, as opposed to rod cells that work better in dim light. If the retina is exposed to an intense visual stimulus, a negative afterimage will be...
s in the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, 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
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
.
Anatomy
The sloth has nine cervical vertebrae, giving it extreme flexibility. As a result, a pale-throated sloth can bend its head backwards and forwards through 270° and rotate it through 330°. The females have two mammae in the chest region, a simple uterusUterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
. Males have no discrete prostate gland, no scrotum
Scrotum
In some male mammals the scrotum is a dual-chambered protuberance of skin and muscle containing the testicles and divided by a septum. It is an extension of the perineum, and is located between the penis and anus. In humans and some other mammals, the base of the scrotum becomes covered with curly...
, and only rudimentary seminal vesicle
Seminal vesicle
The seminal vesicles or vesicular glands are a pair of simple tubular glands posteroinferior to the urinary bladder of male mammals...
s.
The mouth is lined by a black colored mucosa, although the large and heavy tongue is pink. The palate is wrinkled in texture, and the tongue is lined with numerous grooves, apparently adaptations to the sloth's diet. Like other three-toed sloths, it has just five teeth on each side of the upper jaw, and four on each side of the lower jaw; these are all simple and rounded in shape, with the front teeth in the upper jaw being much smaller than the others. The esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
is short, but the stomach is large and complex, and there is also a large diverticulum
Diverticulum
A diverticulum is medical or biological term for an outpouching of a hollow structure in the body. Depending upon which layers of the structure are involved, they are described as being either true or false....
in the cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...
.
Distribution and habitat
The pale-throated sloth is found only in the tropical forests of northern South America, including GuyanaGuyana
Guyana , officially the Co-operative Republic of Guyana, previously the colony of British Guiana, is a sovereign state on the northern coast of South America that is culturally part of the Anglophone Caribbean. Guyana was a former colony of the Dutch and of the British...
, Suriname
Suriname
Suriname , officially the Republic of Suriname , is a country in northern South America. It borders French Guiana to the east, Guyana to the west, Brazil to the south, and on the north by the Atlantic Ocean. Suriname was a former colony of the British and of the Dutch, and was previously known as...
, French Guiana
French Guiana
French Guiana is an overseas region of France, consisting of a single overseas department located on the northern Atlantic coast of South America. It has borders with two nations, Brazil to the east and south, and Suriname to the west...
, western Venezuela
Venezuela
Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...
and Colombia
Colombia
Colombia, officially the Republic of Colombia , is a unitary constitutional republic comprising thirty-two departments. The country is located in northwestern South America, bordered to the east by Venezuela and Brazil; to the south by Ecuador and Peru; to the north by the Caribbean Sea; to the...
, and Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
north of the Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
. There are no recognised subspecies.
Behavior and biology
Pale-throated sloths are solitary, herbivorous animals that spend almost their entire lives in trees. Depending on habitat, ppopulation densities of anything from 1.7 /km2 have been reported. They eat only leaves, including those of CecropiaCecropia
Cecropia is a Neotropical genus presently consisting of sixty-one recognized species with a highly distinctive lineage of dioecious trees....
, Ceiba
Ceiba
Ceiba is the name of a genus of many species of large trees found in tropical areas, including Mexico, Central America, South America, The Bahamas, Belize and the Caribbean, West Africa, and Southeast Asia...
, Elizabetha
Elizabetha
Elizabetha is a genus of flowering plants in the legume family, Fabaceae. It belongs to the subfamily Caesalpinioideae....
, and Hevea
Hevea
Hevea is a genus of flowering plants in the spurge family, Euphorbiaceae. It is also one of many names used commercially for the wood of the most economically important species H. brasiliensis.-Selected species:* Hevea benthamiana Müll.Arg....
. Known predators include jaguar
Jaguar
The jaguar is a big cat, a feline in the Panthera genus, and is the only Panthera species found in the Americas. The jaguar is the third-largest feline after the tiger and the lion, and the largest in the Western Hemisphere. The jaguar's present range extends from Southern United States and Mexico...
s, margay
Margay
The Margay is a spotted cat native to Middle and South America. Named for Prince Maximilian of Wied-Neuwied, it is a solitary and nocturnal animal that prefers remote sections of the rainforest. Although it was once believed to be vulnerable to extinction, the IUCN now lists it as "Near Threatened"...
s, harpy eagles, and anaconda
Anaconda
An anaconda is a large, non-venomous snake found in tropical South America. Although the name actually applies to a group of snakes, it is often used to refer only to one species in particular, the common or green anaconda, Eunectes murinus, which is one of the largest snakes in the world.Anaconda...
s.
The Pale-throated sloth can hang so securely with its hooklike claws that it even falls asleep in this position. It may even stay suspended in the trees for some time after it dies. They have been reported to spend over eighteen hours each day asleep, and move through the tree canopy only very slowly. They periodically descend from the trees to defecate, depositing a pile of small pellets in a hole dug into the ground. Despite their arboreal lifestyle, they are effective swimmers. Their call is a bird-like whistle described as an "ai-ai" sound.
In addition to their mutualism with green algae, pale-throated sloths are also commensal with sloth moth
Sloth moth
Sloth moth is a generic term used to refer to coprophagous moths which have evolved to exclusively inhabit the fur of sloths and to use sloth dung as a substrate for the early stages of reproduction....
s, and with certain species of beetle. These insects live in the sloth's fur, and lay their eggs in its dung, on which their larvae feed.
Reproduction
Mating takes place in the trees, with the pair either face to face, or with the male on the female's back. The female gives birth to a single infant after a gestationGestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
period of about six months.
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 300 grams (10.6 oz). They begin to take solid food at three weeks, and are fully weaned
Weaning
Weaning is the process of gradually introducing a mammal infant, either human or animal, to what will be its adult diet and withdrawing the supply of its mother's milk.The process takes place only in mammals, as only mammals produce milk...
some time after the first month. The young initially have soft greyish-brown fur, which darkens and becomes rougher as they age. They reach sexual maturity at around three years.