Researchers have discovered a 300,000-year-old skull in eastern China that defies categorization among premodern human fossils. This finding could potentially indicate a new branch in the human family tree. The skull, specifically the mandible or lower jaw, was excavated in 2015 alongside 15 other specimens from the late Middle Pleistocene period. This era, starting around 300,000 years ago, was a crucial time for the evolution of hominins, species closely related to humans.

Published on July 31 in the Journal of Human Evolution, the study reveals that the mandible, referred to as HLD 6, possesses unexpected characteristics and doesn’t fit into existing taxonomic groups. Previously, Pleistocene hominin fossils discovered in China posed classification challenges and were seen as anomalies. However, recent research, including this discovery, is reshaping knowledge of the evolutionary patterns in this period.

Upon comparing HLD 6 to Pleistocene hominins and modern humans, researchers identified features of both. The mandible shares a similar shape with Homo sapiens, modern humans evolved from Homo erectus. Yet, it also shares a trait with another branch that stemmed from Homo erectus, the Denisovans. Notably, like the Denisovans, HLD 6 lacks a chin.

María Martinón-Torres, a study author, explained that while HLD 6 doesn’t possess a true chin, it displays faint traits that hint at this characteristic seen in H. sapiens. This amalgamation of primitive and H. sapiens-like features makes HLD 6 unique among the earliest known fossil populations in Asia.

The researchers propose that HLD 6 belongs to a classification that remains unnamed and that modern human traits could have emerged as early as 300,000 years ago, predating the appearance of modern humans in East Asia.

Considering the age of the individual to which the jawbone belonged is important, as skull shapes differ between children and adults. HLD 6 is believed to have belonged to a 12- to 13-year-old. Although an adult skull of the same species was unavailable for comparison, the researchers found consistent shape patterns across Middle and Late Pleistocene hominin skulls of similar ages, supporting their theory.

María Martinón-Torres emphasized that further research is necessary to accurately position HLD 6 in the context of human evolutionary history, stating that “more fossils and studies are necessary to understand their precise position in the human family tree.”

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