for National Geographic News
Researchers believe a jawbone found in Khorat, Thailand, and dating to the Late Miocene era between seven and nine million years ago belongs to a newly discovered relative of orangutans.
The jawbone from the new hominoid, named Khoratpithecus piriyai, is similar to the lower jaw, or mandible, of modern orangutans. And like today's orangutans, the ancient jawbone shows no evidence of anterior digastric muscles, the tell-tale muscles used to lower the jaw in most other primates.
The ancestry of orangutans is highly disputed. While one hypothesis maintains that orangutans originated from Lufengpithecus, a South Chinese and Thai hominoid, another theory says they originated from Sivapithecus, a Miocene hominoid from Indo-Pakistan.
The new discovery, however, suggests that the orangutan's most recent ancestors evolved in equatorial forests similar to those in Southeast Asia that the orangutan inhabits today.
"The [discovery] challenges the place of all the other miocene fossil hominoids as close orangutan relatives," said Jean-Jacques Jaeger, a professor of paleontology at Montpellier II University in France, who led the study.
The research is described in this week's issue of the science journal Nature.
Modern orangutans hail from the Pleistocene period, two million to 100,000 years ago. While their geographic distribution once included much of Southeast Asia, they became extinct from many areas through hunting and deforestation. Today, the orangutan is found only in Borneo and Sumatra.
The jawbone, along with some fossil elephant teeth, were found in 2002 in Khorat, in northeastern Thailand, by a sandpit worker. He sold the fossils to a private Thai collector. A group of Thai scientists, informed about the discovery, convinced the collector to give it to a public museum in Thailand so it could be studied by Thai hominoid expert Yaowalak Chaimanee.
A first look at the jaw shows that it's different from all other fossil hominoids and more similar to large, existing apes. The jaw has a wide incisor-canine area. The symphysis, or fusion of the two halves of the lower jaw, is also similar to modern apes.
The newly discovered jawbone also shares some important characteristics with the jaw of the orangutan. Neither shows evidence of anterior digastric muscles, which act to lower the jaw in many primates.
"[That] one specialized character is uniquely shared with orangutans indicating very close affinities," said Jaeger.
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