We now know what killed humans’ largest relative – and it’s eerie

A scattering of fossilised teeth and four jawbones recovered from caves in the Karst plains of southern China are all that remain of history’s biggest primate – the three-metre tall, orangutan-like Gigantopithecus blacki.

The hulking 300-kilogram primate evolved 2 million years ago and roamed Pleistocene forests until it vanished. Exactly when and why Giganto went extinct has been a tantalising holy grail in palaeontology.

Now Australian researchers have led a massive analysis of Giganto teeth to pinpoint the reason for the giant ape’s doom. And the answer is eerily prescient: the Giganto failed to adapt to a changing climate.

“Gigantopithecus blacki really is one of the biggest mysteries in palaeontology,” Associate Professor Kira Westaway, who co-led the study from Macquarie University, said.

“We only know this species from teeth and parts of jawbone. That’s it – nothing from the neck down. That’s amazing considering it was around for at least 2 million years.”

An artist impression of a group of G. blacki within a forest in southern ChinaCredit: Garcia/Joannes - Boyau (Southern Cross University)

Six Australian universities dated Giganto teeth with different techniques to narrow down the extinction window to between 295,000 and 215,000 years ago.

Westaway specialises in a type of dating called luminescence dating, which involves pinpointing a light-sensitive signal found in quartz or feldspar that builds the longer fossil sediment lies in the dark.

“You can imagine my lab is pretty stressful,” Westaway said. “If somebody comes in with a mobile phone, that’s 10 years worth of work all ruined in a couple of seconds. I’m like the light police.”

Establishing the extinction window allowed the researchers to deduce what might’ve triggered Giganto’s downfall.

Ancient pollen grains alongside the fossilised teeth showed there was still forest around when Giganto vanished, busting the idea they died because their habitat morphed into grassland.

Associate Professor Kira Westaway works with a red light to avoid ruining the light-sensitive signals she uses to date fossils.Credit: Louis Douvis

But by the time Giganto died out, the climate had shifted to become more seasonal. Suddenly, the fruits it gorged upon became sporadic rather than year-round as weather grew variable.

So why did this shift spell the end of the Giganto, while its close neighbour, the orangutan – which lived in the same forests with a similar diet – prevailed?

Southern Cross University geochemist Dr Renaud Joannes-Boyau analysed isotopes within the teeth and scoured them for pits and scratches to infer how Giganto reacted to the changing climate.

The analysis showed Giganto fell back on fibrous, nutrient-scarce twigs and bark foraged from the forest floor.

Restrained by their massive bulk, they were unable to roam and adapt like their smaller, agile orange cousins, which nourished themselves on a rich diet of shoots, leaves, insects, nuts and fruit from the high canopy.

It wasn’t the climate change, per se, that killed the Giganto, Westaway said. “It was the way they responded to it.”

The mountainous location of two caves in southern China where fossils of the largest-ever primate have been found.Credit: Yingqi Zhang

The findings have implications for the conservation of orangutans and mountain gorillas under modern-day anthropogenic climate change, Westaway said.

The research will feature on the front cover of Nature, one of the world’s most prestigious science journals. Within her findings, Westaway sees an implicit lesson for the Giganto’s modern relatives.

Digging into the hard cemented cave sediments containing a wealth of fossils and evidence of G. blacki in a southern China cave.Credit: Kira Westaway

“We’re facing major climate changes, and the Giganto couldn’t even adapt to these very small climate changes … It’s a bit worrying really, isn’t it?”

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