It was the largest primate ever to roam the earth, but exactly why – and when – our distant cousin “giganto” became extinct was something of a mystery.
Now researchers say the enormous ape was the victim of an unfortunate choice of food when its preferred snacks became scarce.
Gigantopithecus blacki roamed mainland Southeast Asia 2 million years ago, with estimates suggesting it was three meters tall and weighed 200-300 kg – about three to four times the weight of a human.
Previous studies have shown that giganto’s range declined significantly by about 330,000 years ago, but tracing the cause of its extinction has been a challenge since it was unclear when exactly it was wiped out.
Dr Kira Westaway of Macquarie University, co-lead author of the study, said: “If you don’t have an accurate timeline, then you’re just looking for clues in the wrong places.
“It was assumed that the decline in forests was the cause of its demise, as it could not live in open grasslands – but our study shows that it [shift to savannah] occurred at approximately 200,000 [years ago] when G black was already extinct.”
Write in the journal Nature, Westaway and colleagues report how they used a host of techniques to date giganto teeth from 11 caves in China, as well as the cave sediments. They also dated sediments from 11 caves where no giganto remains were found.
The results revealed that giganto became extinct between 295,000 and 215,000 years ago. The researchers then pieced together the environmental conditions in which giganto lived by analyzing pollen, animal fossils and sediments within the caves, along with stable isotopes of carbon and oxygen.
The results suggest that around 700,000 to 600,000 years ago, giganto’s environment began to shift from dense forests with patches of grassland, to more open forests – apparently a result of climate change away from fairly stable conditions.
“We get a very strong wet season and a very strong dry season,” Westaway said.
This changed the forest plant communities, and meant that fruits that were available all year round were scarce during drier periods.
The team investigated the changing diet of giganto by analyzing wear patterns on its teeth as well as its internal chemical composition. They compared the findings with those of the Chinese orangutan, a close relative that became extinct much later.
The results point to the orangutan feasted on leaves and flowers of the forest canopy instead of fruit. However, Giganto – which was less mobile and capable of feeding – took a different approach. “The key to [the apes’] survival was what they used as a fallback,” Westaway said. “Giganto chose a very inedible back food – he ate really fibrous things like bark and twigs on the floor.”
About 300,000 years ago, giganto populations were struggling. “Giganto, being a very specialist forager and habitat specialist, really couldn’t adapt,” Westaway said.
Prof Hervé Bocherens from the University of Tuebingen, who was not involved in the study, said earlier research of his too emphasized that a lack of flexibility was behind giganto’s demise, suggesting that it stuck to a diet of plants from a densely forested landscape, even when other species in the same location consumed grass from savannah environments.
But, he added, “Our previous work did not benefit from the same robust chronological framework as this new paper, so we were unable to develop a scenario as detailed as the authors did.”
Westaway said the research had important implications, given concerns about a sixth mass extinction. “It’s really important to understand how primates respond to environmental stress and how some species are more vulnerable and some are more resilient,” she said.