A 300,000-year-old skull recovered from an archaeological dig in China could prompt a new branch on the human family tree. The development comes after scientists have spent years studying the skull and puzzling over its combination of archaic and modern features.

The new paper published in the Journal of Human Evolution joins an existing call to found a new human species closely related to our Homo Sapiens.

The study is the first attempt to fully classify the skull and its features of a flat face and teeth of a modern human. These characteristics clash with other skulls derived from earlier in evolutionary history, including the flattened chin of a Denisovan, and the skull cavity and jaw of a more archaic human.

Fossils That Don’t Fit the Mold

The proposal wades into a long-running controversy over how to classify China’s many human fossils, which often don’t fit neatly into existing categories, including modern-day humans, European Neanderthals and the Denisovans of Asia.

Read More: Who Were the Denisovans?

Over the past 50 years, archaeologists have recovered many fossils in the country that resembled modern Homo sapiens but with many archaic characteristics. Some researchers have thought the specimens must represent a midway point between our ancient forebear, Homo erectus, and modern humans.

“However, such an opinion has never been widely accepted,” says the new paper.

Many of the fossils have come from the Middle Pleistocene age, the period between 126,000 years and 770,000 years ago, a crucial time for human evolution.

Genetic Intermediaries?

In the past 10 years, archaeologists working in China have discovered even more ancient specimens.

They’ve given them a variety of names: East Asian Middle Pleistocene hominins, the population of unclear taxonomic status, the East Asian variant of Neanderthals, and simply “Non-Erectus.”

And one more name: Homo sapiens. Some researchers have argued that the Middle Pleistocene mystery bones mark the transition between archaic and modern humans, who strode onto the scene some 160,000 years ago.

The new skull does have modern human features, but the paper says they are “weakly expressed” when compared to fossils from the more recent Late Pleistocene.

Two Skulls

In 2021, different groups of researchers reported on the discovery of a massive ancient skull in northeastern China that was at least 146,000 years old. The big noggin sent out reverberations through ancient hominin archaeology, and certain scientific teams called for a new early human species.

Based on the “Harbin” skull, it would hew closer to modern humans than Neanderthals or other archaic groups.

One of the related papers stated that the human fossils from Hualongdong area (that of the new skull) resemble the Harbin cranium, which has a similar shape.

As if accepting the invitation, the new paper also calls for a new lineage “that is neither H. erectus nor Denisovan but one that is phylogenetically close to H. sapiens.”

“It is likely that during this period several hominin lineages or taxa coexisted,” the paper says, “but only some of them may be considered putative ancestors to H. sapiens.”

Read More: When Did Homo Sapiens First Appear?