The Tapanuli orangutan (Pongo tapanuliensis) is a recently identified great ape species, adding a third distinct lineage to the known orangutan family. It represents the first new great ape species described in nearly a century. Its identification highlights the planet’s rich biodiversity and the ongoing need for conservation.
The Story of Discovery
Recognition of the Tapanuli orangutan as a distinct species involved decades of observation and scientific analysis. An isolated population in the Batang Toru area of South Tapanuli, Sumatra, was first reported in 1939. This did not lead to species recognition then. The population was rediscovered in 1997, but researchers initially believed these were Sumatran orangutans. Over the next decade, the Sumatran Orangutan Conservation Programme (SOCP) studied the population, establishing a research station by 2006 to investigate their behavior and genetics.
In 2013, scientists examined the skull of a male orangutan from Batang Toru. This skull exhibited anatomical differences, particularly in the jaw and skull, compared to other orangutan populations. This finding prompted an extensive genomic study, which analyzed genetic samples from 37 wild orangutans across Sumatra and Borneo. This genetic and morphological analysis provided strong evidence that the Batang Toru population represented a unique evolutionary lineage. On November 2, 2017, an international team of scientists officially announced the Tapanuli orangutan as a new species, publishing their findings in the scientific journal Current Biology.
Unique Characteristics
The Tapanuli orangutan is distinguished from Bornean (Pongo pygmaeus) and Sumatran (Pongo abelii) orangutans by morphological and genetic traits. While resembling Sumatran orangutans in body build and fur color, Tapanuli orangutans have frizzier hair, smaller heads, and flatter, wider faces. Their skulls are also smaller and differently shaped.
Skeletal differences include:
Larger upper canines
A shallower face depth
A shorter pharyngotympanic tube
A narrower maxillary incisor row
Dominant male Tapanuli orangutans have prominent mustaches and large, flat cheek pads (flanges) covered in fine, blonde hair. Genetically, Tapanuli orangutans diverged from Sumatran orangutans approximately 3.4 million years ago and from Bornean orangutans about 674,000 years ago. Their long calls also differ in maximum frequency, duration, and pulse count from the other two species. Their diet includes unique items such as caterpillars and conifer cones.
Habitat and Conservation Status
The Tapanuli orangutan occupies a highly restricted geographic range in the Batang Toru ecosystem, located in the Tapanuli region of North Sumatra, Indonesia. This population is found in fragmented rainforests, primarily in upland areas between 300 and 1,300 meters above sea level. The isolated nature of this habitat contributed to its late discovery.
With an estimated population of fewer than 800 individuals, the Tapanuli orangutan is classified as Critically Endangered by the International Union for Conservation of Nature (IUCN), making it the most endangered great ape species. The species faces primary threats of habitat loss and fragmentation from human activities. These threats include conversion of forests for agriculture (particularly palm oil plantations), mining operations, and the construction of hydroelectric dams, such as the Batang Toru hydropower project. These developments destroy habitat and fragment forest blocks, isolating populations and hindering genetic diversity, a concern given their slow reproductive rates.