The first 3D virtual reconstruction of a Neanderthal ribcage has revealed that they had straighter spines and a greater lung capacity than modern humans. The findings about the Neanderthal, also spelled Neandertal, were published Tuesday in the journal Nature Communications.
"Neandertals 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," said Patricia Kramer, corresponding study author and professor in the University of Washington department of anthropology. "Understanding their adaptations allows us to understand our own evolutionary path better."
The skeleton, first uncovered in 1983 in Israel's Kebara Cave, is considered to be the most complete Neanderthal remains to date -- although it's missing a cranium. In life, the male Neanderthal, known as Kebara 2 or K2, stood around 5 1/2 feet tall and weighed 166 pounds. He walked the Earth 60,000 years ago and died at 32 years of age.
Kebara 2 is one of several Neanderthal remains recovered from this cave.
Researchers from Spain, Israel and the United States worked together on the study. "Three continents, three languages, one fascination with how the world worked for our shared ancestors," Kramer said.
The international team of researchers used CT scans of K2's fossils to recreate a 3D model of his chest and focused on reconstructing the thorax. The thorax comprises the rib cage and upper spine, forming a cavity that houses the lungs and heart.
These rare Neanderthal bones are typically fragile, and it's easier and less risky to assemble them using a virtual method.
"The shape of the thorax is key to understanding how Neandertals moved in their environment because it informs us about their breathing and balance," said Asier Gomez-Olivencia, lead study author and Ikerbasque Fellow at the University of the Basque Country.
The Neanderthal thorax has actually been the subject of debate among scientists for years due to the stereotypical view of "hunched-over cavemen" based on studies from the 19th and 20th centuries.
The researchers used scientific 3D software, medical scans of the skeleton and direct observations of the K2 skeleton, currently at Tel Aviv University, to piece together their ancient puzzle.
"This was meticulous work," said Alon Barash, a co-author of the study and lecturer at Israel's Bar Ilan University. "We had to CT scan each vertebra and all of the ribs fragments individually and then reassemble them in 3D."
They also compared the medical scans of the bones along with those of modern adult men.
The completed puzzle revealed that Neanderthal ribs connected to the spine more inwardly, which forces the chest cavity out and causes the spine to tilt back. The result is a spinal column that lacks the lumbar curve of modern humans.
"I am really curious about how the straightness of the Neandertal lower back, combined with the shape of the ribcage, impacts forces in the lower spine and pelvis," Kramer said. "Modern humans and the other hominins that preserve this region have a lumbar curve but not Neandertals. Why? As a structural engineer and functional morphologist, these questions of shapes connected to behaviors fascinate me."
The researchers called this difference "striking." This skeletal structure not only provided Neanderthals with more stability, but allowed for a larger diaphragm and more lung capacity.
"The wide lower thorax of Neandertals and the horizontal orientation of the ribs suggest that Neandertals relied more on their diaphragm for breathing," said Ella Been, study co-author and physical therapist at 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 researchers have no reason to believe that this is specific to the Neanderthal skeleton they studied because these traits are shared by other Neanderthal bones that have been analyzed.
But it opens up new questions as to why Neanderthals had such a different skeletal structure. Perhaps they needed a larger lung capacity to survive climate change, support their large body masses and support a rugged hunter-gatherer lifestyle.
"The study that I am most interested in pursuing is what this difference in the body shape means for how Neandertals moved around in their world," Kramer said. "Mobility is a fundamental aspect of an individual's life, as anyone who has ever had an injury to their lower body or limbs knows, so I can't help but wonder what this information will allow us to learn about how they walked, how they carried their possessions and their babies, how their groups moved on foraging trips and who went along in the group, and where they might have travelled."
The 3D modeling used in the study could open up this field of research. If Kramer could apply it to any fossil, she said she would love to virtually reconstruct the famed Lucy fossil.
"Having a virtual reconstruction allows us to do all sorts of new computer modeling," Kramer said. "For me, though, the most exciting piece is thinking about the impact of a differently shaped body on mobility. With the computer models, we can begin to 'reanimate' them to see how they moved on hills, for instance, or how carrying burdens impacted their movements."
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