An international team of researchers has unearthed a 13-million-year-old fossil of a newly discovered ape species in Uttarakhand, which is the earliest known ancestor of the modern-day gibbon.
The finding, published in the journal Proceedings of the Royal Society B, fills a major void in the ape fossil record and provides important new evidence about when the ancestors of today's gibbon migrated to Asia from Africa.
The fossil, a complete lower molar, belongs to a previously unknown genus and species (Kapi ramnagarensis), and represents the first new fossil ape species discovered at the famous fossil site of Ramnagar in nearly a century.
The researchers, including those from Arizona State University in the US and Panjab University in Chandigarh, were climbing a small hill in an area where a fossil primate jaw had been found the year before.
While pausing for a short rest, the team spotted something shiny in a small pile of dirt on the ground.
"We knew immediately it was a primate tooth, but it did not look like the tooth of any of the primates previously found in the area," said Christopher C Gilbert, from City University of New York in the US.
"From the shape and size of the molar, our initial guess was that it might be from a gibbon ancestor, but that seemed too good to be true, given that the fossil record of lesser apes is virtually nonexistent," Gilbert noted.
He explained that there are other primate species known during that time, and no gibbon fossils have previously been found anywhere near Ramnagar.
Since the fossil's discovery in 2015, years of study, analysis, and comparison were conducted to verify that the tooth belongs to a new species, as well as to accurately determine its place in the ape family tree, the researchers said.
The molar was photographed and CT-scanned, and comparative samples of living and extinct ape teeth were examined to highlight important similarities and differences in dental anatomy, they said.
"What we found was quite compelling and undeniably pointed to the close affinities of the 13-million-year-old tooth with gibbons," said Alejandra Ortiz, from Arizona State University, who is part of the research team.
"Even if, for now, we only have one tooth, and thus, we need to be cautious, this is a unique discovery.
It pushes back the oldest known fossil record of gibbons by at least five million years, providing a much-needed glimpse into the early stages of their evolutionary history," said Ortiz.
The researchers noted that the age of the fossil, around 13 million years old, is contemporaneous with well-known great ape fossils.
This provides evidence that the migration of great apes, including orangutan ancestors, and lesser apes from Africa to Asia happened around the same time and through the same places, they said.
"I found the biogeographic component to be really interesting," said Chris Campisano from Arizona State University.
"Today, gibbons and orangutans can both be found in Sumatra and Borneo in Southeast Asia, and the oldest fossil apes are from Africa.
"Knowing that gibbon and orangutan ancestors existed in the same spot together in northern India 13 million years ago, and may have a similar migration history across Asia, is pretty cool," Campisano added.