A fossil thigh bone creates a plot twist in the story of human evolution. This partial femur -- found among remains of China's mysterious "Red Deer Cave people" -- belongs to an ancient species of human thought to be long extinct, researchers say. This suggests the ancient species actually survived at least until the last Ice Age 14,000 years ago and overlapped with modern humans.

The fossil's true identity was discovered by researchers from the University of New South Wales (UNSW) and the Yunnan Institute of Cultural Relics and Archaeology (YICRA, China). The femur was originally excavated from Yunnan Province's Maludong (Red Deer Cave) in 1989, but it remained unstudied in a museum in southeastern Yunnan, according to a news release.

While the fossils have not yet been assigned to a particular species, researchers say the thigh bone exhibits features that strongly resemble those of Homo habilis and early Homo erectus, which lived more than 1.5 million years ago in Africa. It follows then that early hominins may not have immediately disappeared in China after modern humans emerged.  

"The new 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," Associate Professor Darren Curnoe, study leader from UNSW, explained in the university's release

After analyzing the thigh bone, researchers believe the Red Deer Cave people had a gait that was different than ours, and that they were relatively small compared to pre-modern and Ice Age human standards.

"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," Professor Professor Ji Xueping, co-author of the study from YICRA, added.

Their study was recently published in the journal PLOS ONE

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