Nominate bears in India were found to weigh average 93.2 kg (205 lb) in males and 83.3 kg (184 lb) in female per one study. The average weight of sloth bears from the nominate subspecies in Nepal was 95 kg (209 lb) in females and 114 kg (251 lb) in males. Exceptionally large specimens of females can scale up to 124 kg (273 lb) and males up to 192 kg (423 lb). Sloth bears adults are a medium-sized species though weight can range variously from 55 to 105 kg (121 to 231 lb) in typically-sized females and from 80 to 145 kg (176 to 320 lb) in typically-sized males. Skulls of a Sri Lankan sloth bear (left) and a common sloth bear (right) from the Muséum national d'histoire naturelle

The sloth bear shows evidence of having undergone a convergent evolution similar to that of other ant-eating mammals. Sloth bears probably arose during the Middle Pliocene and evolved in the Indian subcontinent. 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. The fossilised 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. A fragment of fossilised humerus from the Pleistocene, found in Andhra Pradesh's Kurnool Basin is identical to the humerus of a modern sloth bear. Sloth bears may have reached their current form in the Early Pleistocene, the time when the bear family specialised and dispersed. But due to wide-scale conversion of upland forests into tea and coffee plantations, it is now restricted to the northern and eastern lowlands. Īt the turn of the century, the Sri Lankan sloth bear occurred throughout Sri Lanka. It has much shorter body hair, and sometimes lacks the characteristic white chest mark. The Sri Lankan sloth bear is smaller than the nominate subspecies, has a smaller skull with a condylobasal length of about 250 mm (9.8 in) in females and about 264 mm (10.4 in) in males. Sloth bear occurs in protected areas such as Shoolpaneshwar, Ratanmahal, Jessore, and Balaram Ambaji Sanctuaries. It is absent in the high mountains of Himachal Pradesh and Jammu and Kashmir, the northwestern deserts of Rajasthan, and a broad unforested swath in the south, where Mount Abu Wildlife Sanctuary is located. The sloth bear is the most widespread bear species in India, where it mostly occurs in areas with forest cover, low hills bordering the outer range of the Himalayas from Punjab to Arunachal Pradesh.

This is the nominate subspecies and has a large skull with a condylobasal length of about 290 mm (11 in) in females and about 310 mm (12 in) in males.

Sloth bears have been tamed and used as performing animals and as pets. Historically, humans have drastically reduced these bears' habitat and diminished their population by hunting them for food and products such as their bacula and claws. When their territories are encroached upon by humans, they sometimes attack them. Sloth bears breed during spring and early summer and give birth near the beginning of winter. It shares features of insectivorous mammals and evolved during the Pleistocene from the ancestral brown bear through divergent evolution. It is lankier than brown and Asian black bears. It has a long, shaggy fur, a mane around the face, and long, sickle-shaped claws. It has also been called 'labiated bear' because of its long lower lip and palate used for sucking up insects. It is listed as vulnerable on the IUCN Red List, mainly because of habitat loss and degradation. The sloth bear ( Melursus ursinus) is a myrmecophagous bear species native to the Indian subcontinent.

Sloth ears