The butchered remains of extinct elephant birds could push back the date of human habitation of Madagascar by 6000 years, according to a controversial study published in Science Advances.

The analysis of leg and foot bones from two species of Madagascan elephant bird – Aepyornis and Mullerornis – revealed grooves and indentations that the authors say are consistent with the half-tonne birds having met their demise at the hands of prehistoric humans hunting in the swamplands of Madagascar’s central tablelands.

Radiocarbon dating of the oldest bones puts the time of death at around 10,500 years ago, towards the start of the Holocene period, which marks the end of the last ice age.

The discovery rewrites the history of human arrivals – from Africa to the West and Southeast Asia to the East – on the remote Indian Ocean island. It could also force a re-think of the role humans played in the extinction, around 1000 years ago, of the island’s megafauna, which included hippopotamuses, giant tortoises and giant lemurs, as well as the massive elephant birds.

“What this tells us is that humans were present much earlier in Madagascar, and they could have been living side-by-side, only causing limited hunting pressure upon the animals for 9000 years,” says James Hansford from the Zoological Society of London’s Institute of Zoology, UK, who led the study.

But the claim is a controversial one.

“It’s a fascinating finding,” says Simon Haberle from the Australian National University. But, he adds, “at the moment, there’s not a lot of other evidence to support this finding”.

Haberle has looked at the tell-tale changes to Malagasy vegetation and fire patterns that accompany human occupation. This, along with archeaeological evidence of established villages, points to human settlement of Madagascar only around 1500 years ago.

Other evidence, such as small stone tools found in the north of the island and cut-marked giant lemur and hippopotamus bones, winds back the clock of human occupation to around 4000 years ago. But not everyone is convinced by these dates.

Ratcheting the date back a further 6000 years based on the elephant bird bone cut-marks, is, according to Haberle, “a leap too far,” especially without ruling out damage that could have occurred during fossilisation or excavation.

Alison Crowther from the University of Queensland, Australia, agrees. “The cut marks will need to be really closely scrutinised,” she says.

Even when taken on face value, Crowther is wary of what the finding means.

“There is a strange paradox here,” she says. “These finds of cut-marked bones seem to predate any evidence of humans. Not only is there an absence of human remains [from that time], but there is an absence of human artefacts.”

Such artefacts should include tools large enough to butcher the giant birds. Aside from small tools, only a single undated axe has ever been found on Madagascar.

Hansford stands by his team’s work.

“This paper will undoubtedly cause some controversy, but it really is very strong evidence,” he says.

An absence of cracks around the cut-marks, for instance, clearly shows that the bones were the soft, wet bones of a fresh kill when they were cut. Damage caused centuries later, perhaps by careless excavation of the remains, would have produced obvious fractures as well as contrasting colours on the inside and outside of the cuts, he says. But this wasn’t the case for the elephant bird bones.

“The fact that no-one’s looked at [elephant birds] properly is perhaps one of the reasons this information hasn’t been uncovered before,” he says.

Hansford hopes the find will prompt closer investigations of early Holocene sediments for evidence of human occupation of Madagascar, an island whose prehistory is ripe for scientific discovery.

He’s not alone. “We definitely need more archaeological evidence to put these findings into context,” says Crowther. “It will be interesting to see how well these findings stand up to the test of time with further research and I expect there will be a lot of discussion and debate around this evidence.”