Mysterious skull points to a possible new branch on human family tree

A 300,000 year-old fossilized skull discovered in China is proving to be an evolutionary puzzle. The specimen dating back to the late middle Pleistocene doesn’t look like other skulls that have been found from this time period, and could possibly point to a previously unknown human species. The findings were published late last month in the Journal of Human Evolution. A team of scientists from institutions in Spain, the United Kingdom, and China found the lower jaw–or mandible–and 15 other separate specimens in eastern China’s Hualongdong region in 2015. The mandible in question is named HLD 6 and dates back to an important period in hominin evolution, just before some of the traits that are still seen in modern humans began to evolve in East Asia.

The study noted that HLD 6 was “unexpected” since it doesn’t currently fit into any known taxonomic groups. The skull has similar facial features to those of early modern humans. The skull could potentially belong to a direct human ancestor called Homo erectus sometime between 550,000 and 750,000 years ago.

However, it also shares some of the characteristics of the Denisovans, who belong on a different branch on the human family tree than Homo Erectus. HLD 6 does not appear to have a chin, just like previously discovered Denisovan specimens. Denisovans are now extinct and split from Neanderthals about 400,000 years ago.