Thomas Langur is a species of primate in the family Cercopithecidae. It is endemic to northern Sumatra, Indonesia. Its natural habitat is subtropical or tropical dry forests. It is threatened by habitat loss. Its native names are reungkah in Acehnese and kedih in Alas.
When searching through tropical rainforests, rubber plantations, and both primary and secondary forests, one is able to encounter Thomas’s langur. Since it is arboreal, one usually needs to search high in the trees to find this unique species. However, its positioning in the trees depends on what time of day it is. While it is taking a nap during the day, it selects a tree that tends to have lots of twigs and leaves for protection from the harsh sunlight. However, when it is sleeping at night, it sleeps in the top of a tall tree that faces the open areas. (Colijn and Muchtar, 1996; Flannery, 2004; Gurmaya, 1986)
Presbytis thomasi has a very distinct appearance. Due to their unique facial coloration, it is easy to distinguish North Sumatran leaf monkeys from other primates. The white fur on the underside and arms (which contrasts with the black fur surrounding the rest of the body) continues up around the neck. Two other white stripes, starting from the top of the head, run down the sides, come together in a V-shape at the eyes and encircle them. A purple-silver colored inner layer forms rings around the orange-brown eyes. Inside of the dark tint, one can see the pinkish skin of Thomas’s langur. This same pinkish skin covers the muzzle.