The 300,000-year-old jawbone was found in Hualongdong, in China’s Far East, a site where a number of relics and remains have turned up.
It looks like a human, and to all intents and purposes is a human. But its curious mixture of various traits has thrown scientists’ efforts to determine exactly what species of human it belonged to.
Traits found in the mandible belong to both modern and ancient hominids, something that hasn’t been seen before.
Analysing the unique remains, researchers say the owner of the mouth could well be an unknown ancestor of both modern humans and Neanderthals.
The almost complete jawbone was found alongside a partial skull and a few leg bones.
After conducting detailed tests, scientists found it resembled the same piece of bone found in Late Pleistocene hominids and modern humans.
In the Journal of Human Evolution, the researchers noted: “However, the weak expression of all these features indicates that this mandible does not possess a true chin.”
The lack of this feature places the ancient human closer to older species from the Middle Pleistocene than to modern-day humans.
“Moreover, a suite of archaic features that resemble those of Middle Pleistocene hominins includes pronounced alveolar planum, superior transverse torus, thick corpus, a pronounced endocondyloid crest, and a well-developed medial pterygoid tubercle,” the study’s authors wrote.
Generally, the characteristics are more closely related to the species Homo Erectus, which went extinct around 108,000 to 117,000 years ago.
For reference, our species, Homo Sapiens, only evolved in Africa around 300,000 years ago, showing just how long Erectus had lived before the next generation of humans came about.
Researchers say the mosaic morphological pattern — where evolutionary changes occur in some parts of the system without changes in others — has never been seen in a Middle Pleistocene hominid from East Asia.
It suggests that modern human traits began appearing in ancient species some 300,000 years ago.
Throwing yet more confusion into the mix, the team found that the facial bones were more similar to those of modern humans than the jawbone itself.
The researchers write: “Even though the predominantly modern human-like morphological features in the […] facial bones suggest that [the specimen] bears similarities to modern humans, the mosaic morphological pattern of the […] mandible revealed in the present study supports the complicated morphological diversity that existed in the late Middle Pleistocene hominin record in East Asia.”
Other mosaic morphologies have been seen in China previously attributed to Denisovans, an extinct species of humans that roamed Asia during the Lower and Middle Paleolithic periods, stretching from around 300,000 years ago to 50,000 years ago.
But this new discovery, given that it features a combination of traits, may belong to “a third lineage that is neither H. erectus nor Denisovan but one that is phylogenetically close to H. sapiens.”
“In this context, the population represented by [this specimen] could have some phylogenetic relationship with late Middle to Late Pleistocene hominins (H. sapiens, Neanderthals, and Denisovans) and share with them some of their features,” they conclude.
