Beginning about 2.6 million years ago, giant primates almost 10 feet tall weighing 551 pounds roamed the plains of southern China. Gigantopithecus blacki (G. blacki) towered over today’s largest monkeys by about five feet and is believed to be the largest primate to ever roam the Earth. However, it went extinct just as other primates–like orangutans–were thriving.
Now, a team of scientists from China, Australia, and the United States believe that this giant ape went extinct between 295,000 and 215,000 years ago because it could not adapt its food preferences and behaviors and was vulnerable to extreme changes in the planet’s climate. The findings are detailed in a study published January 10 in the journal Nature.
“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,” Yingqi Zhang, study co-author and Institute of Vertebrate Palaeontology and Palaeoanthropology at the Chinese Academy of Sciences (IVPP) paleontologist, said in a statement.
Roughly 700,000 to 600,000 years ago, the rich forest environment that G. blacki lived in began to change. The new study proposes that as Earth’s four seasons began to strengthen and G. blacki’s habitat saw more variability in temperature and precipitation, the structure of these forest communities began to change.
In response, G. blacki’s close relatives the orangutans adapted their habitat preferences, behavior, and size over time. However, G. blacki was not quite as nimble. Based on its dental anatomy, these giant apes were herbivores that had adapted to eat fibrous foods like fruits. However, when its favorite food sources were not available, the team believes that G. blacki relied on a less nutritious backup source of sustenance, decreasing the diversity of its food. They likely suffered from a reduced geographic range for foraging, became less mobile, and saw chronic stress and dwindling numbers.
“G. blacki was the ultimate specialist, compared to the more agile adapters like orangutans, and this ultimately led to its demise,” said Zhang.
Honing in on a date
G. blacki left behind roughly 2,000 fossilized teeth and four jawbones that helped paleontologists put together the story of G. blacki’s time on Earth, but more precise dating of these remains was needed to determine its extinction story. To find definitive evidence of their extinction, the team took on a large-scale project that explored 22 cave sites in a wide region of Guangxi Province in southern China.
Determining the exact time when a species disappears from the fossil record helps paleontologists determine a timeframe that they can work to rebuild from other evidence.
“Without robust dating, you are simply looking for clues in the wrong places,” Kira Westaway, a study co-author and geochronologist at Macquarie University in Australia, said in a statement
In the study, the team used six dating techniques the samples of cave sediments and teeth fossils. The techniques produced 157 radiometric ages that were combined with eight sources of environmental and behavioral evidence. They took this combined figure and applied it to 11 caves that had evidence of G blacki in them and 11 caves of a similar age range that did not have any remains of G. blacki.
The primary technique that helped the team hone in on a date range was luminescence dating. It measures a light-sensitive signal that is found in the burial sediments that encased the G. blacki fossils. Uranium series and electron-spin resonance were also critical in dating the G. blacki teeth themselves.
“By direct-dating the fossil remains, we confirmed their age aligns with the luminescence sequence in the sediments where they were found, giving us a comprehensive and reliable chronology for the extinction of G. blacki,” Renaud Joannes-Boyau, a study co-author and geochronologist at Southern Cross University in Australia, said in a statement.
Building a world from teeth and pollen
Researchers also used a detailed pollen analysis to reconstruct what the plant life looked like hundreds of thousands of years ago, a stable isotope analysis of the teeth, and a detailed analysis of the cave sediments to re-create the environmental conditions leading up to the time G blacki went extinct. Trace element and dental microwear textural analysis of the apes’ teeth enabled the team to model what G. blacki’s behavior likely looked like when they were flourishing, compared to their demise.
“Teeth provide a staggering insight into the behavior of the species indicating stress, diversity of food sources, and repeated behaviors,” said Joannes-Boyau.
The dates of the fossils combined with the pollen and teeth analysis revealed that G.blacki went extinct between 295,000 and 215,000 years ago, earlier than scientists previously assumed. The team believes that studying their lack of adaptation has implications for today’s changing climate and the need for adaptation.
“With the threat of a sixth mass extinction event looming over us, there is an urgent need to understand why species go extinct,” said Westaway. “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.”