The Tapanuli orangutan (Pongo tapanuliensis) is a species of orangutan restricted to South Tapanuli in the island of Sumatra in Indonesia. It is one of three known species of orangutan, alongside the Sumatran orangutan (P. abelii), found farther northwest on the island, and the Bornean orangutan (P. pygmaeus). It was described as a distinct species in 2017. As of 2018, there are roughly 800 individuals of this species and it is currently on the critically endangered species list.[

Discovery and naming - An isolated population of orangutans in the Batang Toru area of South Tapanuli was reported in 1939. The population was rediscovered by an expedition to the area in 1997, but it was not recognized as a distinct species then.[7] Pongo tapanuliensis was identified as a distinct species, following a detailed phylogenetic study in 2017. The study analyzed the genetic samples of 37 wild orangutans from populations across Sumatra and Borneo and conducted a morphological analysis of the skeletons of 34 adult males. The holotype of the species is the complete skeleton of an adult male from Batang Toru who died after being wounded by locals in November 2013. The holotype is stored in the Zoological Museum of Bogor. The skull and teeth of the Batang Toru male differ significantly from those of the other two orangutan species. Comparisons of the genomes of all 37 orangutans using principal component analysis and population genetic models also indicated that the Batang Toru population is a separate species.

Etymology: The specific name, tapanuliensis, as well as the common name, Tapanuli orangutan, refer to Tapanuli, the hilly region in North Sumatra where the species lives.

Habitat and distribution - Tapanuli orangutans live in tropical and subtropical moist broadleaf forests located south of Lake Toba in Sumatra. The entirety of the species is found in an area of about 1,000 km2 (390 sq mi) at elevations from 300 to 1,300 m (980 to 4,300 ft). Tapanuli orangutans are separated from the island's other species of orangutan, the Sumatran orangutan, by just 100 km (62 mi).

Conservation - With fewer than 800 individuals restricted to an area of about 1,000 km2 (390 sq mi), the Tapanuli orangutan is the rarest great ape. It is listed as critically endangered by the International Union for Conservation of Nature (IUCN) because of hunting, conflict with humans, the illegal wildlife trade, rampant habitat destruction for small scale agriculture, mining and a proposed hydroelectric dam, the Batang Toru hydropower project, in the area with the highest density of orangutans, which could impact up to 10% of its already dwindling habitat and degrade important wildlife corridors. Conservationists predict an 83% decline in three generations (75 years) if the necessary conservation measures and practices are not implemented. Inbreeding depression is likely due to the small population size and fragmented range. This is supported by the genomes of the two Tapanuli orangutan individuals, which show signs of inbreeding. In August 2019 Swiss environmental group PanEco, which is a partner in the Sumatran Orangutan Conservation Programme, dropped its previous opposition to the dam, several months after firing several researchers who opposed the new strategy.[15] .