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A Gibbon’s Tooth, 13 Million Years Old, Fills Gap in Primate Evolution

By BETH HARPAZ

The discovery of a small, ancient tooth in a pile of dirt in India has turned out to be a missing link in the evolutionary history of apes.

The tooth is 13 million years old and belonged to a previously undiscovered ancestor of the modern-day gibbon. It was found by Professor Christopher Gilbert (The Graduate Center, Hunter College). The discovery is detailed in Proceedings of the Royal Society B.

Gilbert was taking a break while fossil-hunting in Ramnagar, India, in 2015, when he spotted something shiny in the dirt. It was a small molar, about a quarter-inch wide. It took several years of analysis and study to figure out where the tooth fit into the ape family tree. Eventually, the discovery led to the naming of a new genus and species, Kapi ramnagarensis.

Chris Gilbert excavating a fossil near Ramnagar, India.
Photo Credit: Biren Patel

The tooth is significant for several reasons. Gibbons are categorized as lesser (meaning smaller) apes in the ape family, while larger apes like orangutans are categorized as great apes. Scientists knew that lesser apes evolved in Africa around 20 million years ago. But until now, the oldest known lesser ape fossils were only 7 to 8 million years old. Finding this 13 million-year-old tooth fills “one of the biggest gaps in the entire primate record,” Gilbert said. 

The discovery also proves that these ancient gibbons migrated from Africa to Asia at around the same time, and through the same places, as great apes. The fossil record for great apes had previously established their presence in Asia around 13 million years ago, and the tooth that Gilbert found confirms that lesser apes were in Asia by 13 million years ago as well.

“We appear to be catching a window into that event as they pass through South Asia on their way to establishing their recent and current distributions in East and Southeast Asia,” Gilbert said in an interview with The Graduate Center.