Pongo Tapanuliensis - www.batangtoru.org
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Introducing Sumatra’s new great ape species

PONGO TAPANULIENSIS

The ‘Tapanuli Orangutan’ has just been designated as a new species, with the scientific name ‘Pongo tapanuliensis’. It is the newest great ape species in the world, and only lives in the the rugged terrain of the Batang Toru Ecosystem in the three Tapanuli districts of North Sumatra.

The Tapanuli Orangutan was previously believed to be the southernmost populaton of the Sumatran orangutan, Pongo abelii. However, based on multi-disciplinary research efforts over several years by a team of Indonesian and international scientists looking at genetics, morphology, ecology and behaviour, it became clear that the Tapanuli orangutan was in fact closer to the Bornean orangutan, Pongo pygmaeus, than the Sumatran, so it should be considered a separate species. In fact, the research also indicates that it is ancestral to the other species.

Quick facts about Pongo tapanuliensis and their habitat:

  • Less than 800 individuals remain in the wild;
  • They are only found in the Batang Toru Ecosystem, in all three subdistricts of Tapanuli, North Sumatra;
  • In total, the Batang Toru Ecosystem comprises 150,000 hectares, with just 110,000 (1,100 km2) of this as current orangutan habitat;
  • Approximately 85% of the Batang Toru Ecosystem is listed as ‘Protected Forest’, with the remaining 15% of primary forest area listed as ’Other Use Area’ or ‘Logging Forest’;
  • Most of their remaining habitat is above 850m asl;
  • The Tapanuli orangutans are split into 2 main blocks (east and west) by the Sumatran fault line, with a third, smaller population in the Sibuali-Buali Nature Reserve, located adjacent to the west block;
  • Re-establishing connectivity between these three separated populations is key to the survival of the species,  by avoiding inbreeding;
  • Tapanuli orangutans are very slow to breed, with females having their first offspring at around 15 years of age, with the interbirth interval thereafter being approximately 8-9 years.  They can live until 50-60 years of age;
  • The new species designation is based on research in genetics, morphology, and behaviour;
  • This new species is now the rarest and most threatened species of great ape in the world (even rarer than the mountain gorillas of Africa);
  • The Tapanuli orangutan will be included in the IUCN Red List with an immediate entry as ‘Critically Endangered’.

Why is the Tapanuli orangutan a new species?

Genetic differences are the first reason for the differentiation of the Tapanuli orangutan species.  Research indicates that there was a genetic separation from the Sumatran orangutan about 3.38 million years ago, whereas the Tapanuli orangutans split from the Bornean orangutans approximately 670 thousand years ago.

There are also a number of morphological differences seen in the Tapanuli orangutans:

  • The skull and jaw bones of the Tapanuli orangutan are less robust than those of the Sumatran and Bornean orangutans;
  • The hair is thicker and more curly;
  • The male Tapanuli orangutan has a moustache and protruding beard with flatter cheek pads, covered in fine blonde hair;
  • Their molar sizes differ from fossil orangutans (from the Pleistocene period);
  • The Tapanuli orangutan long call differs from that heard in the other two species;
  • They eat plant species that have never been seen consumed by the other orangutan species, including aturmangan (Casuarinaceae) seeds, sampinur (Podocarpaceae) fruits and flowers, and agatis (Araucariaceae).

Living in this high altitude habitat (900-1100 m asl), the Orangutan Tapanuli consume a variety of different food species never seen before in the diet of this great ape. In addition, tool use, so far only found in high-density orangutan populations in lowland swamp forest, has also been found to occur in Batang Toru.