University of Iowa paleoanthropologist Russell L. Ciochon thinks it was even larger.
"We've estimated around nine feet [three meters] tall [when] standing on its hind legs," said the scientist, who calculated its likely dimensions from a jaw bone.
The beast weighed nearly half a ton (500 kilograms), making it more than twice the size of the largest modern ape, Ciochon estimates.
"Clearly it was dramatically bigger than a gorilla," he said. But, like a gorilla, it presumably walked on all fours.
Researchers have wondered whether Gigantopithecus shared a 10-million-year-old ancestor with Asia's only modern great ape, the orangutan.
The extinct giant ape's teeth share many structural traits with those of the purported ancestor, Sivapithecus, indicating that the two species are closely related.
But recent x-rays allowed Ciochon and his colleagues in Germany to peer inside the Gigantopithecus teeth. The scientists concluded that orangutans' teeth aren't similar to the other species, suggesting that the modern primates evolved from a different branch of the ape family, Ciochon says.
Long in the Tooth
Through past studies of Gigantopithecus teeth, Ciochon has determined that the ape subsisted on bamboo and fruits encased in tough coatings.
The Smithsonian's Potts argues that a diet of tough, fibrous vegetation might account for the creature's massive jaws and teethwhether the rest of the animal's body was unusually large has yet to be determined.
"All we know is that they had really whopping jaws and teeth," he said. "There are no limb bones or other bones of the body."
But teeth give Rink, the McMaster University researcher, plenty to work with.
Rink specializes in dating mineral deposits, and he recently focused on Gigantopithecus teeth from a cave in China's Guangxi region. Those mineral nuggets may represent the most recent evidence of the ape.
Using a technique that calculates a fossil's age based on the electron spin, or magnetism, in minerals, Rink recently put an age of about 300,000 years on some of the remains.
While modern people weren't on the scene at that time, early humans called Homo erectus were living in the region.
"[Early] humans were living down in the river valleys," Rink said. "Gigantopithecus was living in the tropical forest at higher elevations. It's likely that Gigantopithecus and humans saw each other in the landscape."
Other experts are more cautious about that conclusion.
"They weren't living side by side," the University of Iowa's Ciochon noted. Tropical forest "is not the primary habitat for humans."
Potts of the Smithsonian said, "Whether they actually frequently saw each other is still unclear."
Nevertheless, Ciochon says, Rink's new results reflect the youngest date yet assigned to Gigantopithecus and may be from close to the time when the species died out.
Even if encounters between species did occur, it was probably environmental changenot hungry humansthat wiped out the giant apes, Ciochon says.
"I think they were pretty much immune to predators," he said, "because they were just too big."
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