A new species of orangutan has been identified in remote Indonesian forests and immediately becomes the most endangered type of great ape in the world with just 800 individuals, scientists said on Thursday.

The Tapanuli orangutan, found only in upland forests in North Sumatra, differs from the other two species of orangutan in the shape of its skull and teeth, its genes, and in the way the males make long booming calls across the jungle, they said.

"The differences are very subtle, not easily observable to the naked eye," Prof. Michael Kruetzen of the University of Zurich, who is part of an international team, told Reuters.

"With no more than 800 individuals, this species is the most endangered great ape," the scientists wrote. Apart from humans, great apes comprise orangutans, gorillas, chimpanzees and bonobos.

New orguntan

The newly discovered Tapanuli orangutan differs from the other two species of orangutan in the shape of its skull and teeth, among other factors. (Maxime Aliaga)

The Tapanuli orangutan had probably been isolated from other populations for 10,000 to 20,000 years, the researchers wrote in the journal Current Biology. The population had been known by scientists since at least 1997 but had not previously been considered a separate species.

The Tapanuli orangutan faces threats including that of forest clearance to make way for mining or palm oil plantations. The region also had plans for a hydroelectric dam.

The scientists urged quick conservation measures. Otherwise, "we may see the discovery and extinction of a great ape species within our lifetime," they wrote.

Baby new species orangutan

A baby Pongo tanapnuliensis, also known as the Tapanuli orangutan, plays in a tree. (Andrew Walmsley)

Laurel Sutherlin of Rainforest Action Network, who was not involved in the study, said the finding "must also serve as a wake up call to all of us from consumers, to global food and paper brands, to investors and local and national governments" to protect forests.