Archaeologists have reassessed the route early humans took to reach Australia – via New Guinea, and not, as previously thought, via Timor.

Thousands of small stone tools and charred fish bones were discovered in a deep cave, the Laili rock shelter, in central-north Timor-Leste. Archaeologists have dated them to thousands of years after humans were believed to have come to the region; before that time, there is no sign of human occupation.

Timor Island has long been considered a stepping stone island for the first human migration between mainland Southeast Asia and into Australia and New Guinea, study co-author Professor Sue O’Connor, from the Australian National University, said.

But this theory has been challenged by the discovery of a human “arrival signature” from about 44,000 years ago, suggesting there were no humans on the island before this time.

Laili rock shelter (unlike other sites in the region) preserves deep sediments dating between 59,000 and 54,000 years ago, which show no signs of clear occupation, Dr Shimona Kealy, from the ANU College of Asia and the Pacific, said.

Humans were also absent throughout the southern Wallachean islands, showing they were “most likely a gateway crossing for ancient humans making the crossing to Australia”, Dr Kealy said. They were not occupied until thousands of years after the initial settlement of Australia, Professor O’Connor believes.

“The absence of humans on Timor Island earlier than at least 50,000 years ago is significant as it indicates that these early humans arrived on the island later than previously believed,” Professor O’Connor said.

“This provides further evidence to suggest early humans were making the crossing to Australia using the stepping stone island of New Guinea, rather than Timor Island as researchers had previously suggested.

Based on the sheer number of artefacts unearthed at the site, the researchers say the migration to Timor Island was a “major” one. They believe these ancient humans likely made the crossing to Timor from nearby Flores Island and mainland Southeast Asia.

“The traditional view held by researchers is that early humans who were making these significant water crossings were stumbling upon these islands by mistake, largely because it was so long ago,” Dr Kealy said.

“Their arrival on Timor was no accident. This was a major colonisation effort, evident through the sheer number of people who were making the journey.

“It’s a testament to these peoples’ level of maritime technology and the boats they created, but also their confidence and competence in braving maritime crossings.”

Co-author Associate Professor Mike Morley, from Flinders University, analysed the sediment from the site at the Flinders Microarchaeology Laboratory.

“The shift from pre-occupation to intensive human activity at the site was very clear in the sediments,” Associate Professor Morley said.

“As soon as people arrived on the scene, their use of the cave was very intensive, with clear evidence of burning and trampling of the shelter floor underfoot.”

“We know these people specialised in making tiny stone tools, but we’re not 100 per cent sure what they were used for,” Dr Kealy said.

“Because a lot of their diet was either shellfish or small animals, you don’t really need big knives to gather that sort of food. But having small, fine tools is useful for things like stripping leaves to then weave into baskets, but also for creating wooden tools.”

The research is published in Nature Communications. This work was led by Dr Ceri Shipton from University College London, and involved researchers from the Australian National University (ANU), Flinders University, the ARC Centre of Excellence for Australian Biodiversity and Heritage, Griffith University, and the University of Wollongong.