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A new great ape species has been discovered in Indonesia’s upland forests by an international team of researchers, including the 1024�˹���.

With no more than 800 individuals, the new species — Tapanuli orangutan (Pongo tapanuliensis) – is the most endangered great ape.

An international team of scientists, including , of the 1024�˹���, described the new species in Current Biology, based on morphological and extensive genomic evidence. The new orangutan species, is endemic to the three Tapanuli districts of North Sumatra, and occurs in roughly 1,100 km2 of upland forest in the Batang Toru Ecosystem.

Lead author Professor Michael Krützen, at the , said: “It is very exciting to describe a new great ape species in the 21st century, although what must be the highest priority now is protecting this new species.

“If steps are not taken quickly to reduce current and future threats to conserve every last remaining bit of forest, we may see the discovery and extinction of a great ape species within our lifetime.”

The discovery of the new great ape species was not straightforward or expected.

Dr Davila Ross, a reader in comparative psychology in the Department of Psychology, has previously studied orangutan calls and their evolutionary history. In her research on long distance calls of the Sumatran and Bornean orangutans, including an acoustic analysis of long distance calls, she found that these calls have a genetic basis, which proved useful information for today’s study.

She said: “The Tapanuli orangutan also differs from other orangutan species in how the adult males produce their long-distance calls, which are known to be genetically rooted.”

Professor Erik Meijaard, who carried out the initial survey south of Lake Toba looking for orangutan populations, said despite nearly 50 years of orangutan research in Sumatra, the Batang Toru population was only ‘rediscovered’ in 1997, during a series of field surveys.

In 2005, the and other non-governmental organisations intensified previous research and conservation efforts on the orangutans in the Batang Toru Ecosystem, together with several universities, and Indonesian authorities. As a part of this effort, a research station was established by SOCP in 2006 allowing for a more detailed look at their behavioral ecology and genetics.

It was not until 2013, when skeletal material from an adult male orangutan killed in a human-animal conflict became available, that SOCP’s Matthew Nowak and colleagues realised the uniqueness of the Batang Toru population.

Anton Nurcahyo, an Indonesian PhD student at the , said: “We compared this skull to other orangutan skulls. We were completely surprised to find that the skull is quite different in some characteristics from orangutan skulls we had seen before.”

While this suggested that the Batang Toru population was potentially unique, much stronger evidence was required to determine whether the Batang Toru orangutans were indeed a different species.

This was achieved by the largest genomic study of wild orangutans to date which has been made possible by decades of data collection at most of the field sites where orangutans are studied.

Dr Maja Mattle-Greminger, who with colleague Dr Alexander Nater was responsible for the genomic analyses at the University of Zurich, said: “For quite some time, we had been working on genomic data to investigate the genetic structure and evolutionary history of all existing orangutan populations.

“One consistent result was that we identified three very old evolutionary lineages among all orangutans, despite only having two species currently described.”

Professor Krützen said: “When we realised that Batang Toru orangutans are morphologically different from all other orangutans, the pieces of the puzzle fell into place.

“The oldest evolutionary line in the genus Pongo is found in Batang Toru orangutans, which appear to be direct descendants of the first Sumatran population in the Sunda archipelago.”

Extensive computer modelling to reconstruct the population history of orangutans, revealed that the Batang Toru population appears to have been isolated from all other Sumatran populations for at least 10,000-20,000 years, after which the low levels of influx of males from the northern populations had stopped. Adding additional evidence based on behavioral observations and ecological surveys from Batang Toru and other sites provided further support for the morphological and genetic findings.

A recent independent study by Indonesian and international scientists indicated that no more than 800 individuals remain in the Batang Toru Ecosystem, making the Tapanuli orangutans the most endangered great ape species.

Clearing forests for mining sites, plans to build a hydro-electric dam, hunting, and general human encroachment are, the scientists say, putting strong pressure on the Tapanuli orangutan.