Primates, especially gibbons and other apes, are rare finds in the Asian fossil record. Fossils from the Pleistocene and Holocene are most often preserved in caves, where live gibbons almost never spend time. But humans preserved the remains of at least one gibbon for posterity by burying it in the tomb of a Chinese noblewoman 2,300 years ago during China’s Warring States Period.

The unfortunate ape was buried with a noblewoman believed to be Lady Xia, the grandmother of Qin Shi Huang, the first Chinese emperor, who ruled from 259 to 210 BCE. Lady Xia also took a leopard, a lynx, an Asiatic black bear, a crane, and several domestic animals with her to her very ornate grave in Chang’an, now the city of Shenheyuan in Shaanxi Province. Morbid menageries are a hallmark of high-status burials from this period, but primatologist Samuel Turvey of the Zoological Society of London says archaeologists have never before seen a gibbon interred this way.

That’s interesting in its own right. By Lady Xia’s day, gibbons had become popular among the nobility as pets and symbols of the class of scholars and officials called Junzi. Thanks to the graceful way they swing through the trees, gibbons were considered noble in ancient Chinese culture. So it’s culturally significant to find a gibbon, presumably a pet, buried with the grandmother of China’s first emperor. But this particular gibbon, besides its proximity to power, may also represent a previously undiscovered—and now extinct—species.

Introducing Junzi imperialis

“While visiting the archaeological collections in Xi'an, Shaanxi Province, in 2009, I found that a semi-complete gibbon skull, mandible, and associated skeleton had been discovered in a recently excavated royal tomb from the old capital of Chang'an,” Turvey told Ars. “Shaanxi is located a huge distance from any of China's surviving gibbon populations, which immediately suggested that this specimen could be something extremely interesting.”

Turvey and his colleagues measured the distances between certain landmarks on the gibbon’s skull, as well as the shape and proportions of the teeth and bones, and compared them to the four genera of gibbons alive today, comprising a total of 18 species—four of which live in China. Lady Xia’s gibbon didn’t match any of them. “This demonstrates that the Xi'an gibbon is distinct at the genus level from all living gibbons, making it only the eighth known ape genus to have survived into the recent historical era,” Turvey told Ars. He and his colleagues named the newly discovered species Junzi imperialis.

Their analysis gets some additional support from geography. Most of the other animals in Lady Xia’s tomb lived in the southern part of Shaanxi Province until fairly recently, which means the gibbon was probably also local. Historical accounts describe gibbons being caught near Chang’an as late as the 10th century CE, and later accounts say that wild gibbons lived in the Shaanxi Province well into the 18th century.

But there are no gibbons in Shaanxi today, and the province is separated from Southwestern China—home to China’s only remaining gibbons—by several rivers and other large drainages.

“Gibbons are extremely vulnerable to habitat fragmentation, as they are almost completely restricted to the forest canopy and are rarely able to cross gaps in the forest,” explained Turvey. Rivers often act as physical barriers between gibbon populations, preventing interbreeding, so it’s reasonably likely that the local gibbon population in Shaanxi was a different species from the gibbons now living in Southwestern China.

“In addition to skeletal differences, living gibbons can be differentiated on the basis of different fur color patterns, especially in their facial patterning and by their species-specific songs,” said Turvey. “Unfortunately, we have no way of knowing what Junzi looked or sounded like in life.”

And even with living gibbons, it can be hard to tell species apart just by looking, which is why zoos so often end up accidentally hybridizing gibbon species. Genetic testing is the best way to be sure, but Turvey and his colleagues weren’t allowed to do destructive sampling of the remains of Lady Xia’s pet gibbon—and Central China’s subtropical climate doesn’t usually lend itself to good DNA preservation anyway. That leaves us with bones and teeth.

Declaring a new species can be a contentious venture, and it will take some time to see whether other primatologists will accept J. imperialis. But the case for J. imperialis was solid enough to get through peer review, and this wouldn’t be the first time a primate species has been accepted on the basis of a single example.

We may have lost more primates than we realize

Until now, scientists assumed that no ape species had gone extinct since the end of the last Ice Age. That assumption is based mostly on the fossil record—if we don't have fossils from primate species that lived during the Holocene and the species doesn't exist presently, there's no reason to think the species ever existed. And thanks to the wet climate, primate remains aren’t preserved often in the tropics, either at archaeological sites or in the recent fossil record—a problem that has also frustrated paleoanthropologists studying early human migrations into the region.

But J. imperialis proves that at least one ape species died off relatively recently, which may force primatologists and ecologists to re-think the assumption that humans only began to threaten the existence of our fellow apes in the last couple of centuries.

“Until the discovery and description of Junzi imperialis, it was thought that apes and most other primates have been relatively resilient to past human pressures on biodiversity and that the worrying global decline of apes was a modern-day phenomenon,” said Turvey. “We're now realizing that there may also have been numerous past human-caused extinctions of apes and other primates before the recent historical era.” The absence of extinct primates from the Holocene fossil record may just mean that tropical and subtropical climates erased the evidence. We may never know what we’ve already lost.

In fact, there could have been several more now-extinct gibbon species in China, Turvey and his colleagues suggest, because historical records describe gibbons living across Central and Southern China, including in several areas separated by large rivers from J. imperialis’ territory near Chang’an and the four gibbon species living in Southwestern China today. So far there’s no direct evidence of any other extinct gibbon species, but their discovery would further challenge our assumptions about how much primate biodiversity we’ve already lost.

An earlier start to the sixth mass extinction

Should we really blame ourselves for the extinction of J. imperialis? It’s hard to say for sure, but humans are the most likely culprits, according to Turley and his colleagues.

“Few extinctions across the climatically stable Holocene can even questionably be interpreted as non-anthropogenic,” they wrote. And a wave of deforestation near Chang’an late in China’s Imperial period would have put serious pressure on gibbon populations. As stated earlier, gibbons’ near-inability to cross gaps in the forest canopy makes them especially vulnerable to deforestation.

“Tropical deforestation causes gibbon populations to quickly become fragmented and isolated, which can rapidly lead to extinction,” Turvey told Ars. And then there’s the fact that gibbons are hunted for food and traditional medicine across much of Asia. In computer models run by Turvey and his colleagues, gibbon population declines follow a wavefront of human population expansion—an ecological smoking gun.

If gibbon species like J. imperialis were already dying off by the 1700s, gibbons may be even more vulnerable to habitat loss and hunting than we thought, which is a sobering thought given how seriously modern gibbons are threatened today. All four of the species still living in China are critically endangered, and only about 26 Hainan gibbons are left, all confined to a single forest patch on Hainan Island.

“The discovery of Junzi imperialis emphasizes the need to focus more conservation efforts on today's surviving gibbon species, especially the four remaining gibbon species in China, which are among the world's rarest and most threatened mammals,” said Turvey.

Science, 2018. DOI: 10.1126/science.aao4903 (About DOIs).