An archaic species of the genus Homo from China, thought to be long extinct, likely survived until as recently as 14,000 years ago, a thigh bone found among the remains of China’s ‘Red Deer Cave people’ suggests.

The 14,000 year-old bone – a partial femur – was found, along with the fossilized remains of mysterious dark-skinned people, in Maludong (Red Deer Cave), Yunnan, Southwest China, in 1989.

According to a study in the journal PLoS ONE, the bone looks like the femurs of early Homo erectus and H. habilis.

“Like the primitive species Homo habilis, the Maludong thigh bone is very small,” explained study co-lead author Prof. Ji Xueping, of the Yunnan Institute of Cultural Relics and Archaeology, China.

“The shaft is narrow, with the outer layer of the shaft (or cortex) very thin; the walls of the shaft are reinforced (or buttressed) in areas of high strain; the femur neck is long; and the place of muscle attachment for the primary flexor muscle of the hip (the lesser trochanter) is very large and faces strongly backwards.”

With an estimated body mass of roughly 50 kg, the Maludong individual was very small by pre-modern and Ice Age human standards.

“The find hints at the possibility a pre-modern species may have overlapped in time with modern humans on mainland East Asia, but the case needs to be built up slowly with more bone discoveries,” said Dr Darren Curnoe of the University of New South Wales, a co-lead author on the study.

The scientists said their discovery is controversial because, until now, it had been thought that the youngest pre-modern humans on mainland Eurasia (Neanderthals and Denisovans) died out 40,000 years ago, soon after anatomically modern Homo sapiens entered the region.

When the same team announced the discovery of the remains of the Red Deer Cave people in 2012, it divided the scientific community.

At the time, the scientists speculated the bones could represent an unknown new species, or perhaps a very early and primitive-looking population of modern humans, which had migrated to the region more than 100,000 years ago.

“We published our findings on the skull bones first because we thought they’d be the most revealing, but we were amazed by our studies of the thigh bone, which showed it to be much more primitive than the skulls seem to be,” Prof. Ji said.

The new discovery once again points towards at least some of the Maludong bones representing a mysterious pre-modern species.

The team has suggested in another recent PLoS ONE paper that the skull from Longlin Cave in China is probably a hybrid between anatomically modern Homo sapiens and an unknown archaic group – perhaps even the one represented by the femur from Maludong.

“The Maludong fossil probably samples an archaic population that survived until around 14,000 years ago in the biogeographically complex region of Southwest China,” the researchers said.

“The unique environment and climate of southwest China resulting from the uplift of the Tibetan Plateau may have provided a refuge for human diversity, perhaps with pre-modern groups surviving very late,” Prof. Ji added.

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D. Curnoe et al. 2015. A Hominin Femur with Archaic Affinities from the Late Pleistocene of Southwest China. PLoS ONE 10 (12): e0143332; doi: 10.1371/journal.pone.0143332