Tapanuli orangutan

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. , there are roughly 800 individuals of this species and it is currently on the critically endangered species list. 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. 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. 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. Genetic comparisons show that Tapanuli orangutans diverged from Sumatran orangutans about 3.4 million years ago, and became more isolated after the Lake Toba eruption that occurred about 75,000 years ago. They had continued sporadic contact that stopped between 10,000 and 20,000 years ago. Tapanuli orangutans diverged from Bornean orangutans about 674,000 years ago.