A thigh bone discovered in China that appears to belong to another species of human could prove that we were not the only Homo species alive at the end of the last ice age.

The bone, which is only about 14,000 years old, is believed to belong to an individual of the so-called "Red Deer Cave people," named after the cave in China where they were found, reports Phys.org. What makes this particular thigh bone so curious is that it has features that resemble those of some of the most ancient members of the human genus, Homo habilis, creatures that existed between 2.8 and 1.5 million years ago.

This means that the bone could provide evidence that at least one mysterious species of proto-human may have retained these ancient features well into modern times.

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"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," said professor Ji Xueping from the Yunnan Institute of Cultural Relics and Archaeology, one of the members of the team who studied the bone.

In other words, though the thigh bone has ancient features, other remains from these individuals, such as their skulls, appear more modern. This strange mix of ancient and modern characteristics means the Red Deer Cave people may have been unlike any other Homo species that existed in the region at any time. It's an evolutionary mystery, to be sure.

Prior to this discovery, it was widely believed that the youngest pre-modern humans on mainland Eurasia — the Neanderthals of Europe and West Asia, and the "Denisovans" of southern Siberia — died out about 40,000 years ago. There is also evidence that another species of human, dubbed Homo floresiensis (sometimes referred to as "hobbits" due to their diminutive size), may have survived on the island of Flores in Indonesia until very recently. But the Red Deer Cave people would have survived even further into modern times than this species.

For now, researchers aren't jumping to any conclusions. It's only one thigh bone, after all. More bones will need to be uncovered and studied before anything definitive can be said about these mysterious humans. Even so, it's an exhilarating find, one that further proves human evolution was a far murkier process than some may have previously believed.

"The riddle of the Red Deer Cave people gets even more challenging now: Just who were these mysterious Stone Age people? Why did they survive so late? And why only in tropical southwest China?" said Darren Curnoe from the University of New South Wales, another of the bone's discoverers.