simakobu, (Simias concolor), leaf-eating monkey found only on the Mentawai Islands west of Sumatra. The body averages about half a metre (20 inches) in length, and it is unique among langurs in having a tail that is much shorter than the body (15 cm [6 inches]). Females weigh 7 kg (15.5 pounds) on average, and males are somewhat larger. Apart from the piglike tail, the most outstanding feature is the fairly prominent and upturned nose. Most simakobu are blackish, but a significant proportion (one-quarter to one- third) of them are creamy buff in colour.
Simakobu are more terrestrial than most leaf-eating monkeys. In some areas they live in monogamous pairs; elsewhere, groups consist of a male and several females. They are often hunted for food by the native people of the islands, and the forests of the Mentawai Islands are increasingly being logged. The simakobu is related to other langurs and to the proboscis monkey; all are primates of the Old World monkey family, Cercopithecidae.