Radiocarbon dating and extensive examinations of giant “elephant” birds indicate ancient humans arrived on Madagascar some 6,000 years earlier than previously believed, according to new research published in Science Advances. But who these people were, how they got there, why they chose the remote tropical island, and where they went remains a mystery.

Researchers examined the fossil remains of the now-extinct Madagascan elephant birds (Aepyornis and Mullerornis) found in a fossil bone bed along the Christmas River in 2009. These flightless megafaunal birds were once widespread across Madagascar, weighing 500 kilograms (1,100 pounds) and stretching 3 meters (10 feet) tall. They were so large, it is thought one egg could feed an entire human family.

It had been thought that as these massive birds went extinct not long after humans arrived, they were probably the cause. However, upon closer inspection, researchers found cut marks and depression fractures located on the birds’ bones, which they say are consistent with hunting and butchery techniques used by much earlier prehistoric humans. This, they conclude, requires a new timeline for the history of the island.

“Humans seem to have coexisted with elephant birds and other now-extinct species for over 9,000 years, apparently with limited negative impact on biodiversity for most of this period," said lead author James Hansford in a statement. 

Previous research on lemur bones and artifacts suggest humans arrived 2,400 to 4,000 years ago. The cut marks are the earliest evidence of humans on the island pushing human occupation back as far as 10,500 years ago.

Madagascar experienced a massive biodiversity loss of megafauna around 1,000 years ago, which, along with the giant birds, included hippos, giant tortoises, and giant lemurs, but it's unclear if humans were involved in their extinction. Archaeological evidence from this time, such as tools or village settlements, hasn’t been found. As is often the case, the discovery creates more questions than it does answers.

"This new discovery turns our idea of the first human arrivals on its head. We know that at the end of the Ice Age, when humans were only using stone tools, there were a group of humans that arrived on Madagascar,” said co-author Patricia Wright. "We do not know the origin of these people and won't until we find further archaeological evidence, but we know there is no evidence of their genes in modern populations. The question remains – who these people were? And when and why did they disappear?”

What we do know is that it extends the archaeological timeframe of the island, and presents a new timeframe for how humans coexisted with megafauna now extinct.