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Our close evolutionary cousins may have had a subtle, but somewhat different breathing mechanism compared to anatomically modern humans, according to a team of scientists who completed the first 3D virtual reconstruction of the rib cage of an adult male Neanderthal.
Reconstruction of a Neanderthal. Image credit: Neanderthal Museum.
The team, led by University of the Basque Country’s Dr. Asier Gomez-Olivencia, focused on the thorax — the area of the body containing the rib cage and upper spine, which forms a cavity to house the heart and lungs.
The researchers worked with a 60,000-year-old skeleton of a male Neanderthal, labeled Kebara 2, which was found in Kebara Cave in Israel in 1983.
Using CT scans of Kebara 2 fossils, they were able to create a 3D model of the chest — one that is different from the longstanding image of the barrel-chested, hunched-over ‘caveman.’
The conclusions point to what may have been an upright individual with greater lung capacity and a straighter spine than today’s modern human.
“The shape of the thorax is key to understanding how Neanderthals moved in their environment because it informs us about their breathing and balance,” Dr. Gomez-Olivencia said.
“And how Neanderthals moved would have had a direct impact on their ability to survive on the resources available to them,” added co-author Professor Patricia Kramer, of the University of Washington.
“Neanderthals are closely related to us with complex cultural adaptations much like those of modern humans, but their physical form is different from us in important ways. Understanding their adaptations allows us to understand our own evolutionary path better.”
Comparison of the Kebara 2 thorax (left column) to the modern human male sample (in gray; middle column) and superposition of the two morphologies (in blue, Kebara 2; in gray, the modern human sample male mean; right column) in cranial (top row), ventral (middle row) and left lateral (lower row) views. Image credit: Gómez-Olivencia et al, doi: 10.1038/s41467-018-06803-z.
Discoveries and studies of other Neanderthal remains in the 19th and early 20th centuries gave rise to theories and images of a stereotypical, hunched-over caveman.
Over time, further research clarified scientific understanding of many Neanderthal traits, but some debate has lingered over the structure of the thorax, the capacity of the lungs and what conditions Neanderthals might have been able to adapt to, or not.
“Over the past decade, virtual reconstruction has become more commonplace in biological anthropology,” Professor Kramer said.
“The approach is useful with fossils such as the thorax, where fragile bones make physical reconstruction difficult and risky.”
Nearly two years ago, the same team created a virtual reconstruction of the Kebara 2 spine, the first step in updating theories of Neanderthal biomechanics.
For their model of the thorax, the scientists used both direct observations of the Kebara 2 skeleton and medical CT scans of vertebrae, ribs and pelvic bones, along with 3D software designed for scientific use.
“In the reconstruction process, it was necessary to virtually ‘cut’ and realign some of the parts that showed deformation, and mirror-image some of those that were not so well-preserved in order to get a complete thorax,” Dr. Gomez-Olivencia said.
The reconstruction of the thorax, coupled with the team’s earlier finding, shows ribs that connect to the spine in an inward direction, forcing the chest cavity outward and allowing the spine to tilt slightly back, with little of the lumbar curve that is part of the modern human skeletal structure.
“The differences between a Neanderthal and modern human thorax are striking,” said co-author Dr. Markus Bastir, a researcher at the Laboratory of Virtual Anthropology at the National Museum of Natural History.
“The Neanderthal spine is located more inside the thorax, which provides more stability. Also, the thorax is wider in its lower part. This shape of the rib cage suggests a larger diaphragm and thus, greater lung capacity,” Dr. Gomez-Olivencia said.
“The wide lower thorax of Neanderthals and the horizontal orientation of the ribs suggest that Neanderthals relied more on their diaphragm for breathing,” said senior author Dr. Ella Been, of Ono Academic College.
“Modern humans, on the other hand, rely both on the diaphragm and on the expansion of the rib cage for breathing. Here we see how new technologies in the study of fossil remains is providing new information to understand extinct species.”
The research is published in the journal Nature Communications.
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Asier Gómez-Olivencia et al. 2018. 3D virtual reconstruction of the Kebara 2 Neandertal thorax. Nature Communications 9, article number: 4387; doi: 10.1038/s41467-018-06803-z
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