Once upon a time giant apes lived around the karst plains of what is now southern China. They stood  three meters tall and weighed 250 kilograms. They were the largest apes ever to have lived on Earth.

Then Gigantopithcus blacki, which resembled upsized versions of orangutans, went extinct. Why this happened has long been a mistery, but scientists now say they know the answer. And this answer, they add, holds a key to the conservation of today’s endangered species.

“The story of G. blacki is an enigma in paleontology — how could such a mighty creature go extinct at a time when other primates were adapting and surviving? The unresolved cause of its disappearance has become the Holy Grail in this discipline,” says Professor Yingqi Zhang, a paleontologist at the Institute of Vertebrate Paleontology and Palaeoanthropology at the Chinese Academy of Sciences.

Zhang was a member of a team of Chinese, Australian and American researchers who set out to solve that enigma. They did so by closely examining some 2,000 fossilized teeth and four jawbones of the giant apes unearthed over the years from 22 caves in Guangxi Province in China.

Based on their high-tech analysis they argue that Gigantopithcus blacki went extinct between 295,000 and 215,000 years ago, well before humans arrived at the scene. That was also well before scientists previously thought these giant apes had died out.

“Teeth provide a staggering insight into the behavior of the species indicating stress, diversity of food sources, and repeated behaviors,” explains geochronologist Renaud Joannes-Boyau of Southern Cross University in Australia, who was part of the research.

As regards a likely reason for their extinction, the apes were so highly specialized in their food preferences and behaviors, the scientists posit, that this limitation doomed them once a changing climate altered the landscape.

“We show that from 2.3 million years ago the environment was a mosaic of forests and grasses, providing ideal conditions for thriving G. blacki populations,” the experts note in their study.

“However, just before and during the extinction window between 295,000 and 215,000  years ago there was enhanced environmental variability from increased seasonality, which caused changes in plant communities and an increase in open forest environments,” they elucidate.

Around 700,000 to 600,000 years ago as the environment became more variable, the structure of forests changed markedly. Orangutans, which are a close relative of G. blacki, adapted in their size, behaviors and habitat preferences to these changing conditions.

Not so their giant cousins. G. blacki continued to “rely on a less nutritious backup food source when its preferences were unavailable, decreasing the diversity of its food. The ape became less mobile, had a reduced geographic range for foraging, and faced chronic stress and dwindling numbers,” according to the experts.

“G. blacki was the ultimate specialist, compared to the more agile adapters like orangutans, and this ultimately led to its demise,” Zhang observes.

The fate of the giant apes provides us with an important lesson for today’s biodiversity and our efforts to protect as much of it as we can in the face of a changing climate and our harmful impacts on nature.

“With the threat of a sixth mass extinction event looming over us, there is an urgent need to understand why species go extinct,” says geochronologist Kira Westaway of Macquarie University.

“Exploring the reasons for past unresolved extinctions gives us a good starting point to understand primate resilience and the fate of other large animals in the past and future.”

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