The faded outline of a hand on a cave wall in Indonesia may be the world’s oldest known rock art, according to archaeologists who say it was created at least 67,800 years ago.

The ancient hand stencil was discovered in a limestone cave popular with tourists on Muna Island, part of south-eastern Sulawesi, where it had gone unnoticed between more recent paintings of animals and other figures.

Beyond providing a minimum age for the cave art, the work furthers thinking on how and when Australia first became settled, with the stencil most likely created by the ancestors of Indigenous Australians.

“There’s a lot of rock art out there but it’s really difficult to date,” said Prof Maxime Aubert, an archaeologist at Griffith University in Queensland. “When you can date it, it opens up a completely different world. It’s an intimate window into the past, and an intimate window into these people’s minds.”

An enhanced image showing the narrow, pointy fingers of the stencil. Photograph: Nature

Fieldwork led by Aubert and Prof Adam Brumm, also at Griffith, has revealed a rich history of cave paintings in Sulawesi, mostly on the island’s south-western peninsula. In one cave, a narrative scene depicting three human-like figures and a wild pig was dated to at least 51,200 years ago.

The latest hand stencil was spotted at Liang Metanduno, a cave on Sulawesi’s south-eastern peninsula. Though faded and partially obscured by a more recent motif on the wall, it was ascribed a minimum age after the team dated tiny calcite deposits that had formed over the top. Humans have painted in the cave for millennia, with fresh images adorning the walls for at least 35,000 years.

It is unclear how humans first migrated from Sunda, the south-east Asian landmass that once connected Borneo, Sumatra and Java, to Sahul, which connected Australia, New Guinea and Tasmania. But the rock art suggests some humans travelled on a northern route that crossed Sulawesi.

The fieldwork to date the cave art was led by a team from Australia’s Griffith University. Photograph: Nature

Because sea levels were much lower at the time, land bridges opened up between some neighbouring islands, but humans would still have needed to island hop to spread across the region. Researchers contest when humans reached Sahul, but Brumm believes the rock art supports evidence that northern Australia was settled at least 65,000 years ago.

The hand stencils were made by spraying mouthfuls of ochre mixed with water over a hand pressed to the cave wall. Like some others on Sulawesi, the Liang Metanduno stencil has narrow, pointy fingers, which the researchers believe was an intentional modification.

Brumm said: “Whether they resemble animal claws or more fancifully some human-animal creature that doesn’t exist, we don’t know, but there’s some sort of symbolic meaning behind them.”

Prof Maxime Aubert working in the cave. Photograph: Nature

Writing in Nature, the authors argue that the tweaks to the hand stencil make the rock art “complex” and so probably the work of Homo sapiens, but other long-gone human species cannot be ruled out. Archaeologists working in Spanish caves have dated ochre wall markings, including hand stencils, to at least 64,000 years ago, making them the work of Neanderthals. The related but little known Denisovans occupied a vast area of Asia and reached as far as Indonesia.

Prof Paul Pettitt, of Durham University, who worked on the Spanish cave markings, said it was not clear whether the pointy-fingered hand stencils in Sulawesi were made on purpose or simply caused by the creator moving their fingers. “To call this complex is rather over-interpreting the hand stencil,” he said.

“In any case, Neanderthals were modifying hand stencils, so why this should be a behaviour restricted to Homo sapiens, and why other potential human groups such as the poorly understood Denisovans couldn’t have created it, is unclear,” he added. “Before writing grand narratives about the complexity and success of Homo sapiens, we really should consider other, potentially more interesting explanations of this fascinating phenomenon.”