Fossil hunters scouring the foothills of the western Himalayas have stumbled upon parts of a jawbone of a primate, belonging to a hitherto unknown species, believed to have lived 13 million years ago on the Indian subcontinent.

The finding, by a team of US and Indian researchers, is important because the newly discovered fossil could belong to a group of primates that may have been the ancestor to two other primate groups - Sivaladapis and Indraloris - that palaeontologists discovered in the mountainous terrains of India and Pakistan in the past. These primitive primates are collectively known as Sivaladapids and believed to be distantly related to the living lemurs of Madagascar.

The fossil find, from the lower Siwalik deposits around Ramnagar in Udhampur district in Jammu and Kashmir, may help scientists solve a major mystery: how this group of primates, which weighed less than 5 kilos, managed to survive when their cousins elsewhere became extinct millions of years ago.

"While many anthropoid primates (early monkey relatives) went extinct in Asia around 34 million years ago, these primates survived until 6 million years ago until more modern monkeys and apes arrived from Africa," says Christopher C Gilbert, anthropologist with Hunter College/City University of New York and lead author of the new study appeared in the Journal of Human Evolution last week.

The team, which also included an Indian palaeontologist Rajeev Patnaik of the Panjab University in Chandigarh, named the fossil Ramadapis sahnii, after Ashok Sahni, doyen of Indian palaeontology, who described the first primate fossil belonging to a Sivalidapid in 1979.

"Even though people have been collecting fossils at Ramnagar for almost 100 years, our study demonstrates that the areas around Ramnagar still hold potential to produce new specimens and inform us about primate diversity and evolution in India approximately 11 to 14 million years ago," says Gilbert.

Significantly, the first primate fossil discovery at Ramnagar was made by US bone collector Barnum Brown from the American Museum of Natural History in 1924 when he found an important fossil jaw of an early great ape (now known as Sivapithecus indicus), which is a close relative of the living orangutan. Subsequently in 1979, Sahni and another US palaeontologist recognised the first Sivaladapid primate from the Siwalik region.

"We know Sivapithecus is closely related to orangutans by the similarities in their teeth and because their faces are nearly identical," says Gilbert.

According to Patnaik, knowing more about species from newly-found fossils also important for other reasons. "They help us understand, the environment, or ecosystems, they lived in," says Patnaik. " R. sahnii, for instance, was arboreal primate (which survives on eating leaves). This gives us an indication that a good patch of forest existed around the region, which is now a rocky terrain, several millions years ago," he explains.

Sahni, professor emeritus at the Panjab University, who is not associated with the present study, says studying these primates can give invaluable insights. "This fossil belongs to a special group of primates who were existing on the Indian subcontinent when the landmass was drifting away from Madagascar towards the Asian plate. They became extinct everywhere else in the world, but survived in India and Pakistan till a few million years ago. They managed to survive because of certain special conditions, that we do not know yet," Sahni, who currently lives in Lucknow, told KnowHow.

According to Gilbert, one hypothesis is that Sivaladapids were able to survive for a long time in part because other primitive monkeys, from whom they faced competition, seemed to have become extinct 35 million years ago. "These Sivaladapids seem pretty specialised in eating a lot of leaves," he says. This could probably explain why these primates went extinct once modern leaf-eating monkeys migrated into Asia from Africa nearly 6 to 7 million years ago.

Scientists like Patnaik argue that discovery of new fossils is always significant as they help molecular biologists to recalibrate molecular clocks which would help them more accurately pinpoint the age of divergence between two species. Molecular clocks are based on the knowledge that certain pieces of DNA accumulate changes at a relatively constant rate, called the mutation rate. "It is the fossil records that help geneticists to determine the mutation rate," says Patnaik.

Gilbert explains it further. "One of the key molecular clock fossil calibration points since the 1980s has been Sivapithecus, which is almost certainly a close relative of the orangutan and helps provide a divergence date for orangutans from African great apes (chimps and gorillas). Because the oldest known Sivapithecus fossils are approximately 12.5 million years old, we infer that orangutans got separated from African great apes for at least 13 million years ago," he says.

This date is further used to help calibrate the molecular clock in certain pieces of DNA among all apes and humans.

"The interesting thing about the Ramnagar fossils is that their exact age is still uncertain, but there is some evidence that they might be older than 12.5 million years, perhaps closer to approximately 13.5 million years. If this is true, then the molecular clock calibration point would have to be adjusted, resulting in slightly different estimates for how long different primate lineages have been separated, including chimps and humans, Gilbert explains.

This could probably explain why a small piece of relic found in a testing terrain like Ramnagar can produce far-reaching changes in our collective evolutionary history.