Severe drought caused by climate change may have led to the decline of Indonesia’s pygmy elephants and the “hobbit”-like humans who hunted them.
Until about 50,000 years ago, Homo floresiensis, standing about a metre tall, thrived on the South Pacific island of Flores by consuming meat from dwarf pachyderms called stegodons.
Researchers originally thought that the tiny hominins – whose bones were discovered in Liang Bua cave in 2003 – died out as recently as 12,000 years ago, possibly because of volcanoes and competition with much larger Homo sapiens.
Advertisement
, however, suggest that both H. floresiensis and its primary prey, Stegodon florensis insularis, actually went extinct about 38,000 years earlier than that – and that modern humans only arrived about 4000 years afterwards. Evidence for catastrophic levels of volcanic activity is also lacking, says at the University of Wollongong in Australia.
Instead, he and his colleagues wondered whether the hominins were victims of climate change, given that most of the annual rainfall in this region comes from summer monsoons – meaning altered weather patterns could have a big impact on survival.
To find out, the researchers took rock samples in a cave 600 metres away from Liang Bua, choosing this alternative location because rocks here had already been precisely dated. They examined the ratios of magnesium to calcium and of different oxygen isotopes within the rocks, which can provide important information about historical seasonal rainfall patterns, says Gagan.
The analysis revealed that the average annual rainfall in the area dropped by 38 per cent between 76,000 and 55,000 years ago, and around 56,000 years ago the climate was 51 per cent drier than it is today.
Monsoons feed year-round rivers, lakes and other freshwater sources, so reduced summer rainfall may have initially led to conflicts over the scant available water, says Gagan.
As the climate continued to turn dry, resources probably dwindled so low that the stegodons – which, like modern elephants, needed large quantities of water – abandoned their homelands in search of water, perhaps along the greener coastal areas, he says. Then, H. floresiensis may done the same, in pursuit of their prey.
Otherwise, if the stegodons had stayed, their population levels would have dropped significantly due to the lack of water, he says. H. floresiensis could have overhunted them to extinction and then moved elsewhere to find food.
Both species would probably have been more vulnerable once outside their native lands, especially if they crossed paths with modern humans, says Gagan. That might have happened, since H. sapiens are very likely to have travelled along the island’s coastlines in boats en route from Asia to Sahul – the ancient paleocontinent that later split into Australia and several nearby islands – .
As for the known volcanic activity in the area between 50,000 and 47,000 years ago, it is possible that this further drove extinction, including through water contamination, says Gagan. Even so, the magnesium and oxygen isotope data suggest that the volcano’s impact may have been fairly limited.
The findings make sense, since water availability is a main driver of change for humans and animals, says at the University of Cambridge. “We know that when water is not available, life can be very difficult.”
While both species had shown a remarkable ability to adapt to the restrictions of island life by taking on dwarf forms, this newly discovered climate change event would have happened too quickly to allow for life-saving mutations, says Leonardi.
Earth arXiv
