Miller’s grizzled langur was thought to be extinct until a team of scientists stumbled upon the large grey monkey outside their previously known habitat.

Scientists have set up camera traps in the Wehea forest in Borneo, to capture images of wildlife including orangutans and clouded leopards, but what they found baffled them at first.

A group of monkeys they initial were unable to identify, has been captured by the cameras. Though the species was documented, illustrations of the monkeys were only available as museum sketches.

It took a while before their suspicions were confirmed. The grizzled langurs were known to exist on Sumatra, Java, Malaysia and north-eastern Borneo, but scientists believed them to be extinct since 2004. Their discovery in Wehea, far east in Borneo, came as a surprise.

“For me the discovery of this monkey is representative of so many species in Indonesia,” said Brent Loken, one of the lead researchers and PhD student at Simon Fraser University in Canada.

“There are so many animals we know so little about and their home ranges are disappearing so quickly,” Loken told The Guardian. “It feels like a lot of these animals are going to quickly enter extinction.”

The team is set to return to the forest to document the grizzly langurs populations whose members have appeared in over 4,000 of the 10,000 images taken over a two-month period.