Image: Tim Laman, Wikimedia Commons

A recent study reveals a third distinct lineage of orangutan — different from its Sumatran and Bornean comrades and surprisingly the oldest species to date.

The discovery began with an injured orangutan reported to the Sumatran Orangutan Conservation Programme. The animal, named Raya, died despite receiving veterinary care, but served as the first specimen of the Tapanuli orangutan ever studied. This new species, Pongo tapanuliensis is determined to be the rarest on the planet, with only 800 individuals remaining in Batang Toru.

The Batang Toru orangutan was initially considered an isolated population of the Sumatran orangutan species. Analysis of Raya’s skull revealed distinct characteristics compared to its Sumatran and Bornean comrades including a shallower face and narrower jawline.

Other distinctions presented by the Batang Toru orangutan include frizzier hair, bearded females, and differences in feeding behavior. Concrete evidence of the new orangutan species was attained through genetic analysis of 37 individuals, revealing very distinct genomes between the Sumatran, Bornean, and Batan Toru populations, although it is surmised that some interbreeding between Batang Toru and Sumatran populations took place. Surprisingly enough, the Batang Toru species is actually more closely related to its Bornean relatives — located more than 620 miles away.

“That was indeed highly surprising because that split is very old and it occurred between two taxa that are only a few hundred [kilometers] away from each other,” Erik Meijaard, an author of the study, told Mongabay.

The Batang Toru population is not only the oldest and rarest orangutan population — it is also the most endangered. The population persists in isolated, divided areas that are threatened by growing human infrastructure, road development, and a plan to build a hydroelectric plant.

“This project … would jeopardize chances of maintaining habitat corridors between the western and eastern range, as well as smaller nature reserves, all of which maintain small populations of P. tapanuliensis,” the researchers explain.

The full study is published in Current Biology.