West Indian Sloths and Two-Toed Tree Sloths: Megalonychidae

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The family Megalonychidae consists of one living genus (JEE-nus), Choloepus, the two-toed tree sloths. A genus is a group of animals within a family that have some similar characteristics. Megalonychidae also includes eleven or more extinct genera ( JEN-uh-rah; the plural of genus). Since the last of the West Indian sloths is dead, scientists have learned about them by studying fossils. From skeletons found in Haiti, researchers determined that the lesser Haitian ground sloth weighed about 50 pounds (23 kilograms) and was as large as a medium-sized dog. It lived on the ground, and probably also spent time in trees.

The lesser Haitian sloth, like the living Choloepus species, had long limbs, long claws, and a broad body. While tree sloths have tiny tails or none at all, this extinct sloth had a long tail that touched the ground. The ground sloth could balance with its tail and then stand on two feet to reach into trees.

Within Choloepus are two living species, Hoffmann's two-toed sloth and Linné's two-toed sloth (also called the southern two-toed sloth). Both use their limbs to hang upside down in trees. Front limbs are slightly longer than back limbs.

Two-toed sloths have small heads and shaggy fur ranging in color from brown to gray. There is a green tint to sloth fur. The color comes from algae (AL-jee), tiny water plants growing in the sloth's hair. The algae, along with the sloth's natural fur color, camouflage (KAM-uh-flaj) the tree-dweller and keep it hidden from predators, animals that hunt it for food. When hungry, sloths may lick the algae on their fur.

The head and body length of two-toed tree sloths ranges from 2 to 3 feet (60 to 90 centimeters). They weigh from 9 to 18 pounds (4 to 8 kilograms). Sloths have eighteen teeth and 3-inch
(7.5-centimeter) claws on each digit of their feet. There are two digits, or toes, on the front feet and three on the back feet. Sloths use their hook-shaped claws to hang from trees and to move.

Sloths may have as many as eight neck vertebrae, or bone segments. Other mammals, including humans, have seven. Two-toed sloths can turn their heads 180 degrees (a half-circle), which gives the sloths a very broad view of their surroundings.


The extinct West Indian sloths lived in the West Indies, in island countries including Haiti. Living two-toed sloth species reside in Bolivia, Brazil, Colombia, Costa Rica, Ecuador, French Guiana, Guyana, Honduras, Nicaragua, Panama, Peru, Suriname, and Venezuela.


The earliest West Indian sloths were arboreal, living in trees. Later species lived both on the ground and in trees. Most two-toed sloths live in trees in the rainforest, an area where there is much rain throughout the year. Sloths also range in cloud forests, forests in high altitude areas that are kept moist by the clouds at that height.


West Indian sloths probably ate leaves. Two-toed sloths are herbivores, eating mostly leaves and twigs. They also eat fruit. Since sloths move from tree to tree, their diet is as varied as the trees they live in.


Two-toed sloths are also known as unau. Their English name, sloth, means laziness. Sloths' diet of leaves produces little energy, so the animals move slowly to preserve that energy. The lack of energy also results in a low body temperature that ranges from 75° to 95°F (24° to 33°C). This wide range is the most varied of any mammal.

The two-toed tree sloths are solitary and remain alone unless breeding or raising their young. After mating, the male leaves. The female gives birth to one young after about eleven months. Gestation, the time a mother carries the baby inside her, may vary by species. A female Linné's two-toed sloth in captivity gave birth five months after mating. Mothers of both species keep the offspring with them for almost a year.

Two-toed sloths spend most of their lives upside down. They eat, mate, and sleep in that position. The low-energy animals may sleep fifteen hours or more a day. These sloths are nocturnal, and are most active at night. During that time, they eat and move from one tree to another. Sloths usually change locations by climbing on tree branches and vines. If this is not possible, the sloth will climb down and move to another tree.


From the earliest times, people probably hunted ground sloths for food and used their fur pelts to make clothing. Scientists study West Indian sloth fossils to learn how these animals evolved and changed over thousands of years. Two-toed sloths were occasionally hunted for their meat.


Sloth is often understood to mean laziness, an undesirable trait. The word "sloth" is a version of the word "slow," which better describes sloths. Their limbs can't support their bodies, so sloths drag themselves on the ground at the rate of 45 feet (13.7 meters) per minute. In trees, sloths move no more than 125 feet (38 meters) per day.


West Indian sloths became extinct two thousand years ago, after people came to the area where they lived. Two-toed sloths lose habitat as forest land is used for lumbering and farms. There is not sufficient information available to determine whether sloths are at risk of extinction, according to the World Conservation Union (IUCN).


Physical characteristics: Hoffmann's two-toed sloths are about 2 feet (60 centimeters) long and weigh up to 18 pounds (8 kilograms). They have coarse fur that is tan colored or grayish brown. Hair color is lighter on the face. Algae adds a green color to the shaggy fur.

Geographic range: Hoffman's two-toed sloths live in Bolivia, Brazil, Columbia, Costa Rica, Ecuador, Honduras, Nicaragua, Panama, Peru, and Venezuela.

Habitat: Hoffmann's sloths live in the tree canopies, near the top of trees in rainforests and cloud forests. They often stay in liana (lee-AN-uh) tangles, twisted vines that provide shelter. The tangle also serves as an alarm. If a predator is approaching, the leaves move and the sloth is alerted about a possible attack.

Diet: Hoffmann's sloths eat leaves, shoots, flowers, and fruit.

Behavior and reproduction: Two-toed sloths are nocturnal, and do not become active until about an hour after the sun sets. Like other sloths, Hoffmann's sloth is solitary. However, a group of sloths may live in one tree. These groups are formed of only female sloths. Males stay on their own unless they are breeding.

After mating, the female sloth gives birth to one offspring in about eleven and a half months. Newborn sloths weigh from 12 to 16 ounces (340 to 454 grams). The mother carries the young sloth on her stomach. Since the offspring eats the same leaves as its mother, the young sloth develops a taste for those leaves. At the age of five months, the young sloth may feed on its own. However, it remains close to its mother for about a year.

Young and adult sloths use their claws and teeth as defenses against predators like harpy eagles, jaguars, and ocelots.

Hoffman's two-toed sloths and people: Sloths are known to heal quickly, so studying them could help scientists understand how to help people heal more quickly.

Conservation status: There is not enough information to determine whether Hoffmann's sloth faces a threat of extinction, according to IUCN. ∎



Attenborough, David. The Life of Mammals. Princeton, NJ: Princeton University Press, 2002.

Squire, Ann O. Anteaters, Sloths, and Armadillos. New York: Franklin Watts, 1999.

Web sites:

Animal Diversity Web. http://animaldiversity.ummz.umich.edu/index.html (accessed on June 30, 2004).

Giacalone, Jacalyn. "Sloths." Mammal Directory.http://www.csam.montclair.edu/ceterms/mammals/sloths.html (accessed on June 30, 2004).

Walker's Mammals of the World Online. http://www.press.jhu.edu/books/walkers_mammals_of_the_world (accessed on June 30, 2004).

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West Indian Sloths and Two-Toed Tree Sloths: Megalonychidae

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West Indian Sloths and Two-Toed Tree Sloths: Megalonychidae