Were Neanderthals cold-adapted or were they just ready for anything? Ribcage reconstruction may hold the answer

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Researchers at the Department of Paleobiology, Museo Nacional de Ciencias Naturales in Madrid report that analysis of a Neanderthal ribcage from a cave in Iraq exhibits a "bell-shaped" thorax configuration typical of Neanderthals elsewhere, differing from that of modern humans.

The findings are published in the Journal of Human Evolution.

Neanderthal ribcage configuration is a subject of great interest to paleoanthropologists due to its implications for physiology, climate adaptation, and diet. Previous research suggests Neanderthals had stockier torsos and larger respiratory systems, potentially adaptations for thermoregulation or high-protein diets.

Previous studies on Neanderthal ribcages have often suffered from incomplete and fragmentary fossil records, limiting some anatomical and functional insights.

A Neanderthal fossil from Shanidar cave in Northern Iraq, named Shanidar 3, is a rarity among Neanderthal fossil records. It is among a small group of skeletal remains almost definitively (though still controversially) laid to rest in intentional burials.

Shanidar 3 likely died from an injury that he initially survived. Previous research has observed that there is a partially healed wound on his ninth left rib, likely the result of a stabbing by a sharp instrument. Based on the deep cut into the rib and incomplete healing of the bone, the wound was likely fatal.

Whether murdered or the victim of an unfortunate hunting accident, Shanidar 3 was buried soon after death. His remains were in an articulated position and had not been disturbed for 45,000 to 60,000 years before discovery. Rib and vertebrae fossils are relatively complete, well-preserved and there is no commingling with other fossils, all particularly suitable conditions for a detailed virtual reconstruction.

Previous reconstructions of Neanderthal ribcages, such as Kebara 2 from Kebara Cave in Israel, have also relied on relatively intact remains.

In the study, titled "Shanidar 3 'rings the bell': Virtual ribcage reconstruction and its implications for understanding the Neanderthal bauplan," researchers from the Museo Nacional de Ciencias Naturales-CSIC, Universidad Autónoma de Madrid, and other institutions performed a virtual reconstruction of Shanidar 3's ribcage.

Through advanced CT scans, missing element estimations, and geometric morphometric analyses, Shanidar 3 exhibited a bell-shaped thorax with ribs that are longer and more horizontally oriented than those of modern humans. This resulted in an expanded lower thorax. The team compared Shanidar 3 to Kebara 2 and 58 globally distributed modern humans grouped by climatic adaptations (cold, temperate, and tropical).

Results show that Shanidar 3 and Kebara 2's ribcages cluster together, separate from modern humans, but closer to cold-adapted modern individuals. Neanderthals showed larger ribcages than modern people from moderate or warmer climates, sharing closer similarity to those adapted to colder climates.

Implications of the results challenge the notion of a Neanderthal ribcage uniquely adapted to cold environments. Shanidar 3 and Kebara 2 both lived in Levantine regions with relatively mild climates, suggesting this morphology was not specific to ecological settings.

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The findings support the picture of a Neanderthal physical build well-suited to many climate types, one of which may have been very cold, across Europe, Asia and the Middle East.

While some Neanderthal evidence exists in what are traditionally cold climates, there is no evidence that they preferred cold weather. Many of the northernmost Neanderthal stomping grounds are thought to have been inhabited primarily in summer seasons.

The larger ribcage affinity in the northernmost modern humans raises new questions about where the current human trait came from. Is this a convergent trait that happens to work well for those in cold climates, or did this trait arrive through genetic exchange with Neanderthals, allowing the modern human offspring to be better adapted?

More information: José M. López-Rey et al, Shanidar 3 'rings the bell': Virtual ribcage reconstruction and its implications for understanding the Neanderthal bauplan, Journal of Human Evolution (2024). DOI: 10.1016/j.jhevol.2024.103629

Journal information: Journal of Human Evolution

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