Stone tools discovered on the island of Sulawesi, Indonesia, date back to at least 118,000 years – suggesting that an archaic human species first colonized the island many millennia before our own species arrived. Exactly who they were, though, remains a mystery. The findings are published in Nature this week.
About a million years ago, a group of hominins (that’s us and our extinct ancestors) settled on the Indonesian island of Flores. Then, about 50,000 years ago, Homo sapiens crossed to Sahul, the landmass that consists of Australia and Papua. Between Sahul and continental Asia lies a vast zone of islands, the largest and oldest among them being Sulawesi. It’s thought to play an important role in both of these dispersal events. Previous studies on rock art in limestone caves revealed that modern humans were living on Sulawesi at least 45,000 years ago.
Between 2007 and 2012, a team led by University of Wollongong’s Gerrit van den Bergh conducted excavations in the Walanae Basin of southwest Sulawesi. They discovered four new sites containing in situ stone artifacts and fossil teeth belonging to megafauna such as the mammoth-like Stegodon, pig-like Celebochoerus, and buffalo-like Bubalus depressicornis.
The team undertook deep-trench excavations at one of the sites, called Talepu (indicated by the arrow in the map to the right), which yielded hundreds of stone artifacts created from silicified limestone cobbles that measure up to 13 centimeters (5.1 inches) in diameter. Most of them were flakes and cores that had been reduced by hard hammer blows to either one face or both faces. These stoneworkers probably weren’t creating tools with a specific form; rather, their stone-flaking produced sharp-edged flakes that they would then use.
With lasers and uranium-series dating, the team revealed that the fossils are between 200,000 and 780,000 years old, while the stone artifacts date back to between 118,000 to 194,000 years. That means they predate the arrival of our species.
Many researchers had previously assumed that the island was only ever colonized by Homo sapiens, but based on these findings, Sulawesi (like Flores) hosted a long-established population of archaic hominins. However, without these Pleistocene Homo fossils, the ancestral origins and identity of these island toolmakers remain unknown. Right now, there are three candidates for potential island colonizers from this region: Homo floresiensis from Flores, Homo erectus from what’s now Java, and the mysterious Denisovans.
“Speculating, I think that a small group of Homo erectus, who we know was around in the region as early as 1.5 million years ago, might have got washed into the sea, perhaps by a tsunami, and might have got stranded on the island Sulawesi, at least more than 117,000 years ago,” van den Bergh tells IFLScience over email. “As you can see there is a lot of speculation here, and there are so many things that we do not know at present, not even the identity of the Talepu toolmaker. The only thing I would dare to put a bet on is that the tools must have been made by pre-modern humans, who somehow must have crossed at least one sea barrier to get to Sulawesi.”
The team thinks that the most likely points of origin would have been Borneo to the west (which would have been part of mainland Asia during periods of low sea level) and the Philippines to the north. That implies that other islands in the area likely harbor undiscovered records of archaic hominins too.
An excavation at the base of Talepu hill in 2012. Dida Yurnaldi
Image in the text: from G.D. van den Bergh et al., Nature 2016