Swinging from branch to branch with loud and often melodic calls, gibbons are a dramatic presence in forests they inhabit. Eighth century Chinese poet Li Bai described their haunting voices: "While on the cliffs of the Yangtze Gorges, gibbons ceaselessly cry/Ten thousand folds of mountains, my skiff has slipped them by."
Today, no gibbons live anywhere near the Yangtze River gorges Li traversed, and the apes that remain elsewhere in China have fur patterns different from those often depicted in classical Chinese paintings. But given their prominence in art, researchers assumed the animals must once have swung through the treetops of central China. Now, physical evidence of a vanished gibbon has turned up in an unexpected place: a tomb that may have been built for the grandmother of China's first emperor, nearly 2300 years ago. The skull and jaw found in the tomb are so distinctive that scientists conclude they belonged to a member of a now-extinct gibbon genus.
The skull "is really a fantastic find," says Thomas Geissmann, a gibbon expert at the University of Zurich in Switzerland who was not involved in the research. "I don't doubt for a second that it's a new species, and probably a new genus. … We can assume that this vast area of central China [once] had many other species" of gibbon. With surviving gibbons also facing extinction, the new find could boost motivation to protect them by highlighting how much has already been lost, says Samuel Turvey, a conservation biologist at the Zoological Society of London who, with his colleagues, describes the ancient skull in this week's issue of Science.
Turvey, who studies human-caused extinctions, combs historical records and museum collections for evidence about past biodiversity. In 2011, at the Shaanxi Provincial Institute of Archaeology in Xi'an, China, he came across artifacts from the tomb, which was discovered in 2004 on the outskirts of Xi'an, the capital of Shaanxi province and once a powerful imperial city. Based on the tomb's location and the artifacts it contained, archaeologists Ding Yan and Zhang Tianen of the Shaanxi institute, who helped lead the excavations, dated it to the Warring States period, about 2250 years ago. They concluded it may have been built for Lady Xia, the grandmother of China's first emperor, Qin Shi Huang. Qin ruled from 256 B.C.E. until 210 B.C.E., united much of China and was buried near Xi'an with his famous terra cotta army.
The collection's primate bones caught Turvey's attention. "Historically there are accounts of gibbons" in central China, he says, "but it is very, very far from any gibbon populations today." The tomb also contained skeletons of leopards, lynx, black bears, cranes, and a range of domestic animals. The wild animals were all from the region, so the gibbon probably also lived nearby, says archaeologist Hu Songmei of the Shaanxi institute. Gibbons were common high-status pets, and burial chambers were often arranged so that the deceased "could continue to enjoy the life they knew when still alive," Hu says. Because the emperor was presumably involved in his grandmother's funeral preparations, Turvey says, "It's not a total flight of fancy to think that he might have seen this specific gibbon."
Chinese authorities did not let the team sample the bone for DNA, which could have helped determine the animal's kinship with existing gibbons. Instead, Turvey worked with Helen Chatterjee, an expert on gibbons at University College London, and colleagues to measure key points on the skull and teeth and compare the dimensions with those of the four living genera of gibbons. Their statistical analysis found both the skull and molars were so distinct from all of today's gibbons that the fossil belonged to a separate genus.
That fits with what we know of gibbons, Chatterjee says. Gibbon populations can easily become isolated from each other because the apes spend their lives in the treetops and can't cross gaps in the canopy created by rivers or other barriers. That has spurred extreme genetic diversity—the four genera alive today have different numbers of chromosomes, she notes.
The team named the new species Junzi imperialis. "Junzi" is a Chinese word for scholar-officials, who were often associated with gibbons because the animals were considered wiser and nobler than mischievous monkeys. The animals' arms were thought to help them channel chi, "a bit like Jedi masters," Chatterjee says.
As for what J. imperialis looked like, classical paintings may hold some clues. They depict gibbons with a wide variety of colors and facial markings, frequently different from any of today's gibbon species. Turvey says J. imperialis "may be the tip of the iceberg," and a whole suite of gibbon species that were common across China in previous centuries have already gone extinct.
The Imperial Chinese reverence for gibbons apparently didn't extend to preserving their habitat. The razing of forests for agriculture in recent centuries, and perhaps the onset of a cooler, drier climate in central China, apparently spelled disaster for J. imperialis. The same dynamic is at play for today's gibbons, says David Chivers, a primatologist who retired from the University of Cambridge in the United Kingdom. One species, on China's Hainan island, has only two dozen individuals left. "Remove the forest and they're gone," he says of the apes. "We've got to stop the forest being cut down. That's the only way to save them."
With reporting by Bian Huihui in Shanghai, China.