A stray molar is the oldest known fossil from an ancient gibbon

Ancestors of these small-bodied apes were in India roughly 13 million years ago, a study suggests

photo of a gibbon looking at the camera

Ancestors of modern gibbons, such as this one, reached what’s now India around the same time as evolutionary precursors of present-day orangutans did, roughly 13 million years ago, a new fossil find suggests.

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While searching for primate fossils in northern India, paleontologist Christopher Gilbert noticed something small and shiny poking out of the dirt. It turned out to be a roughly 13-million-year-old molar from a small-bodied ape related to modern gibbons.

The tooth is the oldest known fossil from a gibbon ancestor, says Gilbert, of Hunter College at the City University of New York. He and colleagues assigned the fossil, which was eroding out of previously dated sediment at a site called Ramnagar, to a new genus and species, Kapi ramnagarensis.

photo of a browned, ancient tooth
This roughly 13-million-year-old molar tooth (shown from above) was found in India and is the oldest known fossil from a gibbon ancestor.C. Gilbert

Until now, the oldest remains of an ancient gibbon species consisted of a small number of teeth found in China, which date from around 7 million to 9 million years ago. Possibly older fossils of a gibbonlike creature are controversial (SN: 10/29/15). Genetic studies of living primates have suggested that gibbon ancestors emerged by at least 20 million years ago in Africa.

After finding the Ramnagar molar in 2015, Gilbert’s team compared it with corresponding teeth of living and extinct apes and monkeys. Features including low, rounded cusps on the edges of the chewing surface link the ancient tooth to modern gibbons and the gibbon predecessor in China, the scientists report September 9 in Proceedings of the Royal Society B.

K. ramnagarensis comes from deposits that previously yielded fossils of an orangutan ancestor, suggesting to Gilbert that both apes reached South Asia from Africa around the same time. “We’re catching a window into that event” as small-bodied gibbons and large-bodied orangutans headed to their recent and current home ranges in East and Southeast Asia, he says.

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