According to a new analysis, a severely fragmented skull excavated along the riverbanks in central China decades ago was once unclassifiable, but is now shaking up the human family tree.

Scientists digitally reconstructed the flattened skull, which is believed to be 1 million years old. Its features suggest that the fossil belongs to the same lineage as the intriguing "Dragon Man" specimen and the Denisovans, a mysterious, recently discovered prehistoric human group with an unknown origin. The age of the skull and its classification as an early Denisovan ancestor imply that this group's origins are much earlier than previously thought.

The newly reconstructed Yunxian 2 skull (center), which was crushed, alongside another flattened skull (left) found at the same site in China.

Researchers published an article in the journal Science on Thursday, stating that they conducted a broader analysis based on the reconstruction and over 100 other skull fossils, depicting a radically different picture of human evolution. These findings significantly alter the timeline of species such as our own, Homo sapiens, and Neanderthals. Neanderthals were ancient humans who lived in Europe and Central Asia before disappearing around 40,000 years ago, and it is known that they coexisted with the Denisovans and interbred with them.

Chris Stringer, a paleoanthropologist at the Natural History Museum in London and head of human evolution research, said in an email, "This changes many ideas because it shows that by 1 million years ago, our ancestors had already split into different groups, indicating that the divergence of human evolution happened much earlier and more complexly than previously thought."

If these findings are widely accepted, they will push back the emergence of our own species by 400,000 years and dramatically reshape our understanding of human origins.

Based on the reconstruction of the Yunxian 2 skull, illustrating what the Yunxian people may have looked like

Confusing ancestors. This skull was one of two partially mineralized specimens unearthed in 1989 and 1990 in Yun County, Hubei Province, central China. According to Stringer, a third skull found nearby in 2022 has not yet been formally described in scientific literature.

"We decided to re-examine this fossil because it has a reliable geological age, being one of the few human fossils from several million years ago," said the study's first author, Professor *** from Shanxi University in China, in a statement. "Fossils of this age are crucial for reconstructing our family tree."

Both Yunxian skulls were deformed due to being underground for thousands of years, but the second one, called Yunxian 2, was better preserved. This specimen formed the basis of the new reconstruction. The new reconstruction used cutting-edge CT scans, optical imaging, and virtual technology to separate the bones from the rock matrix surrounding them and correct the distortions inherent in the fossils.

The age of the skull was determined by the sediment layer where it was found and the mammal fossils discovered in the same layer. Some experts believe it belongs to Homo erectus, a more primitive human species known to have lived worldwide at that time. However, although the large and stocky braincase of Yunxian 2 does resemble Homo erectus, other features of the skull, such as the flat and shallow zygomatic bones, are not similar.

Stringer and his colleagues concluded that Yunxian 2 belongs to an early ancestor of the Dragon Man, officially named the Dragon Man. Scientists discovered the Dragon Man from a skull found in a well in northeastern China in 2021, and the authors of a study published in June used ancient DNA to link the Dragon Man to the Denisovans. The Denisovans are a vague group known from genetic information extracted from some fossil fragments, but are believed to have lived across most of Asia.

The latest analysis also suggests that other difficult-to-classify fossils found in China should be categorized with the Dragon Man and the Denisovans—including fossils of a newly discovered species recently proposed by another research team, which they call the Zhuolu Man, roughly translated as the "Big-Headed Person."

Stringer said that once researchers conduct detailed preparation and study of the third Yun County skull fossil, they will be able to test the accuracy of the reconstruction and its position in the human family tree.

Re-writing history

The skull has prominent bumps and ridges, making it particularly informative in human evolutionary research because it has many features that can be used to identify a new species.

Stringer and his co-author, Professor Ni Xijun from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, used new digital reconstruction information and anatomical data from 104 skulls and jawbones in the human fossil record, applying mathematical procedures used in evolutionary biology to reconstruct the evolutionary relationships between different groups. The team pieced together what is called a phylogenetic tree, showing how different human species have diversified over the past 1 million years.

The analysis shows that the origins of Homo sapiens, the Denisovans, and the Neanderthals are much older than previously thought.

Original: https://www.toutiao.com/article/7554183977465102867/

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