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How Many Tapanuli Orangutans Are Left on Earth?

Examining clues from fur texture and skull shape to DNA, scientists recently discovered a new species of orangutan that happens to be the rarest great ape species on earth.
orangutans, orangutan population, how many orangutans are left, endangered orangutans, orangutans endangered,

A tapanuli orangutan. (World Press Photo/Tim Laman.)

On November 2, scientists revealed they’d identified an entirely new species of orangutan, which is critically endangered and in vital need of protection. Living solely in the secluded Batang Toru forest within Northern Sumatra, Indonesia, the population of Pongo tapanuliensis, or Tapanuli orangutans, hovers around 800, making it the rarest great ape species alive.

Imposing and magnificent, orangutans are the largest tree-dwelling mammals; their name means “person of the forest” in Indonesian and Malay. They tend to be somewhat solitary creatures, swinging from branches, eating fruit, and sleeping while hoisted high in the forest canopy. Previously, scientists classified all orangutans into one of two known species, both also critically endangered: Borneos and Sumatrans. First reported in the 1930s and re-discovered in 1997, orangutans living in Batang Toru were curiosities within the scientific community. Most scientists assumed they were Sumatrans, despite marked behavioral and genetic differences within the population: it wasn’t clear that any of these merited calling the apes a new species.

In 2013, that would all change: that year, researchers gained access to the first skeleton they’d seen from a Batang Toru-native, a male ape they called Raya. Thought to have died due to human-inflicted injuries, Raya provided the first opportunity for scientists to examine an intact skeleton from this largely isolated orangutan population. The ensuing investigation of his physical traits and genetic material revealed powerful-enough differences to constitute classifying the ape as a different species entirely.

After years of research and discussion, an international team of scientists examining Raya published their findings in Current Biology. Specifically, they found that, when compared with 33 adult male orangutan specimens, Raya differed in skull and teeth shape, and that his genome varied significantly from those of 37 other orangutans. Researchers deemed that these differences, taken together, warranted granting a new species designation: thus the Batang Toru-dwellers were classified as Tapanuli orangutans.

Genomic analysis indicated that Tapanulis are genetically closer to Bornean than to Sumatran orangutans, despite their close physical proximity to Sumatran populations. Researchers believe that Tapanulis physically separated from Bornean orangutans around three million years ago, and evolved into a distinct species about 700,000 years ago.

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