A newly published study is shedding light on the anatomical diversity of our extinct relatives, revealing a previously unknown trait in Neanderthals. Researchers have discovered an unfused opening in the first cervical vertebra – a variation also found in a small percentage of modern humans – and its prevalence in Neanderthal fossils suggests a more complex picture of hominin evolution than previously understood. The international study, appearing in The Anatomical Record this month, could reshape our understanding of skeletal advancement and variation across human lineages.
A recently published study has revealed a previously overlooked anatomical feature in Neanderthals – an unfused opening in the first cervical vertebra, also known as the atlas. Researchers say this trait, present in a small percentage of modern humans, could offer new insights into the evolution of our species.
The international research effort, involving specialists from Spain, the United Kingdom, France, and Chile, published its findings in early November in the journal The Anatomical Record.
What did they discover in Neanderthals?
The study centers around an unusual, incompletely closed opening in the atlas (C1) vertebra. Scientists now believe this characteristic may hold important clues about human evolution.
While the C1 vertebra appears small and symmetrical at first glance, analysis of fossilized remains from both pre-Neanderthal and Neanderthal populations revealed the presence of an unfused transverse foramen (UTF) – a variation in anatomy also observed in some people today.
This opening is located on each side of the vertebra and is crucial, as it allows the vertebral artery and several veins to pass through, supplying blood to the brain.
*Neanderthal fossil vertebrae | Asier Gómez-Olivencia et al.
According to a statement from the Universidad Andrés Bello (UNAB), between 8% and 10% of the modern human population exhibits this trait. However, until now, it was unknown whether it also existed in other human species.
The research team, including UNAB Department of Morphology academics Juan José Valenzuela and Mathias Orellana, identified this feature in three fossil atlas vertebrae from different regions of the world.
One specimen originates from the Sima de los Huesos (Burgos, Spain), a Middle Pleistocene site dating back approximately 430,000 years. The other two came from Neanderthal remains discovered in Kebara (Israel) and Krapina (Croatia).
While the sample size is limited, researchers estimate that at least 13% to 20% of Neanderthals may have had this foramen in their C1 vertebra – a percentage equal to, or even higher than, that seen in modern humans. This discovery underscores the anatomical diversity within Neanderthal populations.
What does this trait signify?
This anatomical variation develops during human growth. The C1 vertebra forms during childhood, and the parts that typically cause the UTF usually fuse between the ages of 3 and 4. However, this fusion doesn’t always occur completely, leaving the opening intact.
Juan José Valenzuela, a UNAB academic and one of the study’s authors, explained that “the finding of this trait in fossils from the Neanderthal lineage is particularly relevant because it allows us to explore how certain anatomical variations arose and were maintained throughout human evolution.”
“Vertebrae are fragile bones and often fragmented, making studies of them scarce. Complete specimens are therefore especially valuable,” he added.
The presence of this opening in the first cervical vertebra of Neanderthals raises questions about anatomical diversity within these populations and how subtle changes in development can influence the final shape of the skeleton, according to the study. Understanding these variations can provide a more complete picture of hominin evolution.
Referencia:
Asier Gómez-Olivencia, Mikel Arlegi, Juan José Valenzuela Fuenzalida, Mathias Orellana-Donoso, Juan Luis Arsuaga y Juan A. Sanchis-Gimeno. Unfused transverse foramen of the atlas vertebra in the Neandertal lineage fossils. The Anatomical Record, 2025.
