Researchers have discovered a unique inner ear formation in a 100,000-year-old human skeleton that was believed to be present only in Neanderthals.

The study was conducted by researchers at the Washington University in St. Louis. It was based on CT scan of a fossilized bone in 1970s.

The bone was discovered at the Xujiayao site in China's Nihewan Basin.

Neanderthals are the cousins of humans that separated from the primate line some 400,000 years ago. They then moved to Eurasia and disappeared from Earth 30,000 years ago.

The discovery could provide researchers a clue at inter-breeding between the two groups.

Researchers analyzed the interior configuration of the temporal bone for the study. They discovered that the inner-ear structure resembled that of a Neanderthal than ancient humans, according to the study.

"We were completely surprised," said Erik Trinkaus, PhD, a physical anthropology professor at Washington University in St. Louis, according to the release. "We fully expected the scan to reveal a temporal labyrinth that looked much like a modern human one, but what we saw was clearly typical of a Neanderthal. This discovery places into question whether this arrangement of the semicircular canals is truly unique to the Neanderthals."

The researchers explained in the study that the semi-circular canals in ears are remnants of fluid-filled system that helps humans maintain balance. The inner-ear structure has been used by other researchers as a marker to identify human remains from Neanderthals and other hominid skeletons, according to the study.

The skull used for the study, Xujiayao 15, was discovered along with teeth and bones. The bones are believed to have come from early non-Neanderthal forms of late archaic humans, according to the study.

Trinkaus said that the study adds to current research on human evolution and migration patterns.

"The study of human evolution has always been messy, and these findings just make it all the messier," Trinkaus said in a news release. "It shows that human populations in the real world don't act in nice simple patterns.

Their study was published in the journal Proceedings of the National Academy of Sciences this week.

Xiu-Jie Wu, Wu Liu and Song Xing of the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, and Isabelle Crevecoeur of PACEA, Université de Bordeaux also contributed with the study. 

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