The Tapanuli orangutan was described as a distinct species in 2017.
The species is named Pongo tapanuliensis and lives in the Batang Toru ecosystem of South Tapanuli, on the Indonesian island of Sumatra. Its formal recognition followed a study that combined genetic evidence with measurements of skulls and other skeletal features. The findings showed that this population was not simply a regional form of the Sumatran orangutan.
The population had been reported in the Batang Toru area in 1939 and was rediscovered by researchers in 1997. However, it was not recognized as a separate species at that time. The 2017 study examined genetic samples from 37 wild orangutans and morphological data from adult males, providing the basis for the species description.
The discovery was notable because it produced the first new living great-ape species recognized by science since the bonobo was formally described in the 20th century. It also revealed an unusual evolutionary relationship: Tapanuli orangutans are genetically closer to Bornean orangutans than to the other orangutan species on Sumatra. With fewer than 800 individuals reported in the late 2010s, the species is critically endangered.