Scientists have identified an isolated population of orangutans living in Sumatra in Indonesia, which according to them are "among the most threatened great apes in the world".
The new species named the Tapanuli orangutan (Pongo tapanuliensis) boasts of genetic, skeletal and tooth differences from the two other species of orangutans.
It is the seventh living species of great apes, which besides humans, are the Sumatran and Bornean orangutans, eastern and western gorillas, chimpanzees and bonobos.
"It isn't an everyday event that we find a new species of great ape, so indeed the discovery is very exciting," said Michael Krutzen from the University of Zurich.
However, severely threatened by loss of habitat, hunting and other man-made developments, there are now 800 fewer Sumatran orangutans than previously thought, making them among the most threatened great ape species in the world, the researchers rued.
The orangutans, which were long considered as single species, were first identified in 1997 as two -- one living in Sumatra and the other in Borneo -- in 1997.
The new species lived south of what was the known range for Sumatran orangutans and remained a mystery to scientists until two decades ago.
Apart from genetic, behavioural and ecological evidence, a skeleton belonging to a Batang Toru orangutan, found in 2013, revealed consistent differences in its skull and teeth, making the orangutans living in Batang Toru as a separate specie, the researchers said.
For the study, reported in the journal Current Biology, the team analysed 37 orangutan genomes, which showed that the deepest split in the evolutionary history of living orangutans occurred more than three million years ago, between the Batang Toru population and Bornean orangutans to the north of Lake Toba in Indonesia.
They found that the Bornean and Sumatran orangutans separated only much later, less than 700,000 years ago.
"The Batang Toru orangutans appear to be direct descendants of the initial orangutans that had migrated from mainland Asia, and thus constitute the oldest evolutionary line within the genus Pongo," said Alexander Nater, also from the Unversity of Zurich.
