Humanity has just recognized a new living cousin, but it is even more endangered than other members of the great ape family. The new species, dubbed Pongo tapanuliensis, probably represents the oldest existing orangutan species, but it's restricted to a small patch of Sumatran rainforest and is estimated to number just 800.
The hominid family was once quite diverse, but most of its members are gone. Today it's just us, two species of gorilla, two chimpanzees, and the orangutans. Two decades ago it became accepted that the orangutans of Borneo and Sumatra are actually separate species, P. pygmaeus and P. abelii, an unsurprising finding given that hundreds of kilometers of sea divide them.
Now, in Current Biology, scientists from four continents have made the case that the orangutans that live south of Lake Toba, Sumatra, are a different species from those north of the lake. More remarkably, the north-Sumatran apes are much more closely related to those in Borneo than they are to their relatives a short distance away in the Sumatran forests of Batang Toru.
Although local residents have known about these orangutans for a long time, the outside world only recently became aware the population existed in the region's rugged terrain. Zoologists set out to explore whether there were any differences between this population and the better-known ones, but the task was hampered by reluctance to trap members of such an endangered species. Instead, the researchers relied on genetic analysis of fecal samples, compared with the genomes of 37 orangutans from other areas, and the skull of a single male that had been killed some time before.
The genetics indicated that the newly named Tapanuli orangutans are quite distinct from others. So distinct, the paper's authors argue, they deserve to be regarded as their own species, rather than a Sumatran subspecies. Indeed, the genetics are so different the authors conclude P. tapunuliensis and other orangutans separated 3.4 million years ago. The Bornean and north-Sumatran populations only split into different species 670,000 years ago.
The skull provides an indication of the consequences of the genetic differences. Professor Colin Groves, of the Australian National University (ANU), told IFLScience the skull is smaller than any other known orangutan male at a similar stage of development. On the other hand, the teeth are unusually large, particularly the canines. There are also reports of behavioral differences.
Despite this, P. tapanuliensis orangutans have not been totally isolated from their more numerous cousins. The authors report evidence of gene flow between the Sumatran populations long after they became separate species. Curiously, however, this all seems to have gone one way, apparently because members of the Tapanulis have sometimes come down from the mountains to look for company, while few, if any, of the north-Sumatran orangutans have made the opposite journey. In consequence, P. tapanuliensis appears to be a remarkably well-preserved sample of an ancestral orangutan population.
"Great apes are among the best-studied species in the world," said ANU's Dr Erik Meijaard in a statement. "If after 200 years of serious biological research we can still find new species in this group, what does it tell us about all the other stuff that we are overlooking: hidden species, unknown ecological relationships, critical thresholds we shouldn't cross? Humans are conducting a vast global experiment, but we have near-zero understanding of what impacts this really has, and how it could ultimately undermine our own survival."
P. tapanuliensis orangutans have survived in part because their homeland is too rugged and remote for much human interference, but that may change. A proposed dam would not only remove 8 percent of their range, but also cut across possible migration corridors, increasing inbreeding on both sides. Poaching could become a threat even if the land is unsuitable for the palm plantations that have devastated orangutans elsewhere.
Groves told IFLScience the Indonesian minister for the environment has been alerted to the importance of the issue, but at this point Groves could not point to any specific programs to protect the new species. He suggested those who wish to maintain the hominid family should donate to general orangutan conservation programs such as the Orangutan Conservancy or the Jane Goodall Institute.