The sloth bear (Melursus ursinus), also known as the Stickney bear or labiated bear, is a nocturnal insectivorous species of bears found wild within the Indian Subcontinent. The sloth bear evolved from ancestral brown bears during the Pleistocene and shares features found in insect-eating mammals through convergent evolution. The population isolated in Sri Lanka is considered a subspecies. Unlike brown and black bears, sloth bears have lankier builds, long, shaggy coats that form a mane around the face, long, sickle-shaped claws, and a specially adapted lower lip and palate used for sucking insects. Sloth bears breed during spring and early summer and give birth near the beginning of winter. They feed on termites, honeybee colonies, and fruits. Sloth bears sometimes attack humans who encroach on their territories. Historically, humans have drastically nitially thought to be related to the South American sloths, Shaw and Nodder in 1791 called the species Bradypus ursinus, noting that it was bear-like, but giving weight to the long claws and the absence of upper middle incisors. Meyer (1793) identified it as a bear and called it Melursus lybius, and in 1817, de Blainville called it Ursus labiatus because of the long lips. Iliger called it Prochilus hirsutus, the Greek genus name indicating long lips, while the specific name noted its long and coarse hair. Fischer called it Chondrorhynchus hirsutus, while Tiedemann called it Ursus longirostris.
Sloth bears may have reached their current form in the early Pleistocene, the time when the bear family specialized and dispersed. A fragment of fossilized humerus from the Pleistocene, found in Andhra Pradesh’s Kurnool Basin is identical to the modern sloth bears. The fossilized skulls of a bear once named Melursus theobaldi found in the Shivaliks from the early Pleistocene or early Pliocene are thought by certain authors to represent an intermediate stage between sloth bears and ancestral brown bears. M. theobaldi itself had teeth intermediate in size between sloth bears and other bear species, though its palate was the same size as the former species, leading to the theory that it is the sloth bear’s direct ancestor. Sloth bears probably arose during the mid-Pliocene and evolved in the Indian Subcontinent. The sloth bear bears evidence of having undergone a convergent evolution similar to that of other ant-eating mammals.
Sloth bears are distinguished from Asian black bears by their lankier builds, longer, shaggier coats, pale muzzles and white claws. Adult sloth bears are medium-sized bears, weighing around 130 kg (290 lb) on average, though weight can range variously from 55 to 124 kg (121 to 273 lb) in females and from 80 to 192 kg (176 to 423 lb) in males.They are 60–90 cm (2–3 ft) high at the shoulder, and have a body length of 1.4–1.9 m (4.6–6.3 ft).Females are smaller than males, and have more fur between the shoulders.
Sloth bear muzzles are thick and long, with small jaws and bulbous snouts with wide nostrils. They have long lower lips which can be stretched over the outer edge of their noses, and lack upper incisors, thus allowing them to suck up large numbers of insects. The premolars and molars are smaller than in other bears, as they do not chew as much vegetation. In adults, the teeth are usually in poor condition, due to the amount of soil they suck up and chew when feeding on insects. The back of the palate is long and broad, as is typical in other ant-eating mammals. The paws are disproportionately large, and have highly developed, sickle-shaped, blunt claws which measure 4 in (10 cm) in length. Their toe pads are connected by a hairless web. They have the longest tail in the bear family, which can grow to 6–7 in. Their back legs are not very strong, though they are knee-jointed, and allow them to assume almost any position.The ears are very large and floppy. The sloth bear is the only bear with long hair on its ears.
Sloth bear fur is completely black (rusty for some specimens), save for a whitish Y- or V-shaped mark on the chest. This feature is sometimes absent, particularly in Sri Lankan specimens.This feature, which is also present in Asian black bears and sun bears, is thought to serve as a threat display, as all three species are sympatric with tigers. The coat is long, shaggy, and unkempt, despite the relatively warm enivronment in which the species is found, and is particularly heavy behind the neck and between the shoulders, forming a mane which can be 30 cm (12 in) long.The belly and underlegs are almost bare.