About 50,000 years ago on the Indonesian island of Flores, all the large animals disappeared at once. The losses included dwarf elephants, carnivorous birds – and a species of diminutive hominin known as the “hobbit”, or Homo floresiensis.
It’s not clear why. A volcano erupted, and the climate was shifting. But there is also tentative evidence that there was a new threat on the island: modern humans.
Hobbits were first described in 2004, after bones were found in the Liang Bua cave on Flores. They stood 1 metre tall and had brains the size of grapefruit. Initially it seemed that the hobbits had survived until as recently as 13,000 years ago – suggesting they lived alongside modern humans for tens of thousands of years.
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However, in 2016 researchers led by Thomas Sutikna of the University of Wollongong, Australia reassessed the dating evidence. They found the , implying that’s when they disappeared.
Now Sutikna and his colleagues have dated other material from Liang Bua, revealing how the was changing.
Elephants and birds
They examined over 300,000 animal remains and 10,000 stone tool fragments, found in sediments laid down over 190,000 years. “This is a huge dataset,” says research team member Matthew Tocheri of Lakehead University in Ontario, Canada.
Before 50,000 years ago, Flores was dominated by dwarf elephants (Stegodon florensis insularis) the size of a large cow. “There’s no doubt that this is the largest animal alive on Flores during this time,” says Tocheri.
There were also two large carnivorous birds. Giant marabou storks (Leptoptilos robustus) were 1.8 metres long but otherwise resembled the marabou storks found on African savannahs today. The other bird was a large vulture. Both were scavengers. Flores was also home to Komodo dragons (Varanus komodoensis), the world’s largest lizard.
All four species last appear at Liang Bua 50,000 years ago. The next sediments were laid down 46,000 years ago. “We no longer see those large animals,” says Tocheri. “They’re all gone.”
Today, Komodo dragons survive on Flores’s north coast and on nearby islands. The other three are extinct.
Going boom
The loss of the elephants may have triggered a collapse. “Once Stegodon goes, clearly the marabou stork and vulture disappear right away, because there’s nothing large enough for them to survive on,” says Tocheri. The Komodo dragons retreated to the coast. “They can survive because they eat marine carrion.”
With the elephants gone, the hobbits lost a major food source. So what killed the elephants?
The sediments reveal a big volcanic eruption 50,000 years ago, which caused a pyroclastic flow: a cloud of hot gas and rocks that swept over the ground. “These tend to be the most devastating, because they rip down and burn everything,” says Tocheri.
Eruptions , says Hannah O’Regan of the University of Nottingham, UK. “There have been earlier turnovers where you lose Stegodon and then you get a different [species] recolonising,” she says. It’s possible, then, that the hobbits were driven extinct as an indirect consequence of the volcanic eruption.
But Tocheri points out that Flores is a volcanic island and the elephants – and hobbits – had survived many eruptions. “Generally ecosystems recover quite quickly, within decades,” he says.
Perhaps climate change was a factor instead. “We know that in the broader region of South East Asia, climate changes put these larger animals at risk,” says Tocheri.
Oh no, humans
But the biggest clue comes from the stone tools. Before 50,000 years ago, the tools were mostly made from volcanic rock called silicified tuff – probably by hobbits. After 50,000 years ago, the tools were mostly made of chert. Modern humans preferred using chert, so this may be evidence that our species had arrived on Flores.
Humans may have hunted the elephants; unlike the hobbits, who seem only to have scavenged them. “Modern humans could easily decimate the Stegodon even within a season,” says Tocheri.
Humans were perfectly capable of causing a mass extinction on their own, says John de Vos of the Naturalis Biodiversity Center in Leiden, the Netherlands. Similar pygmy elephants once lived on Mediterranean islands, which do not have volcanoes. They died out when humans arrived.
If humans and hobbits overlapped on Flores, did they interbreed? Tocheri is doubtful, because humans and hobbits are more distinct than humans and Neanderthals. “It all comes down to evolutionary distance,” he says. A study published in August examined the genomes of modern pygmies living on Flores, and found – so there is no smoking gun.
Journal of Human Evolution
