An international team of scientists has completed the first 3D
virtual reconstruction of the ribcage of the most complete Neandertal
skeleton unearthed to date, potentially shedding new light on how this
ancient human moved and breathed.
The team, which included researchers from universities in Spain,
Israel, and the United States, including the University of Washington,
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.
Using CT scans of fossils from an approximately 60,000-year-old male
skeleton known as Kebara 2, researchers 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 study is published Oct. 30 in
Nature Communications.
"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, an Ikerbasque Fellow at the
University of the Basque Country and the study's lead author.
And how Neandertals moved would have had a direct impact on their
ability to survive on the resources available to them, said Patricia
Kramer, professor in the UW Department of Anthropology and corresponding
author on the paper.
"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," she said. "Understanding their
adaptations allows us to understand our own evolutionary path better."
Neandertals are a type of human that emerged about 400,000 years
ago, living mostly from what is today Western Europe to Central Asia.
They were hunter-gatherers who, in some areas, lived in caves and who
weathered several glacial periods before going extinct about 40,000
years ago. Studies in recent years have suggested that Neandertals and
early Homo sapiens interbred, because evidence of Neandertal DNA has
turned up in many populations.
Over the past 150 years, Neandertal remains have been found at many
sites in Europe, Asia and the Middle East. This team worked with a
skeleton labeled Kebara 2, also known as "Moshe," which was found in
Kebara Cave in Northern Israel's Carmel mountain range in 1983. Though
the cranium is missing, the remains of the young adult male are
considered one of the most complete Neandertal skeleton ever found. Two
different forms of dating of the surrounding soil, thermoluminescence
and electron spin resonance, put the age at somewhere between 59,000 and
64,000 years.
Discoveries and studies of other Neandertal 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 Neandertal traits, but some
debate has lingered over the structure of the thorax, the capacity of
the lungs and what conditions Neandertals might have been able to adapt
to, or not.
Over the past decade, virtual reconstruction has become more
commonplace in biological anthropology, Kramer explained. 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 research team created a virtual
reconstruction of the Kebara 2 spine, the first step in updating
theories of Neandertal biomechanics. The team's paper, published in the
book "
Human Paleontology and Prehistory," reaffirmed the likelihood of upright posture but pointed to a straighter spine than that of modern humans.
For this model of the thorax, researchers used both direct
observations of the Kebara 2 skeleton, currently housed at Tel Aviv
University, and medical CT scans of vertebrae, ribs and pelvic bones,
along with 3D software designed for scientific use. "This was meticulous
work," said Alon Barash, a lecturer at Bar Ilan University in Israel.
"We had to CT scan each vertebra and all of the ribs fragments
individually and then reassemble them in 3D."
They then used a technique called morphometric analysis to compare
the images of Neandertal bones with medical scans of bones from
present-day adult men. "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," said Gomez-Olivencia.
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 Neandertal and modern
human thorax are striking," said Markus Bastir, senior research
scientist at the Laboratory of Virtual Anthropology at the National
Museum of Natural History in Spain.
"The Neandertal spine is located more inside the thorax, which
provides more stability," said Gomez-Olivencia. "Also, the thorax is
wider in its lower part." This shape of the rib cage suggests a larger
diaphragm and thus, greater 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 senior author 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."
What that means for how Kebara 2 lived is ripe for further research,
Kramer said. How did Neandertals breathe, and for what physical demands
might they have needed powerful lungs? What does that tell us about how
they moved, and the environment in which they lived? Did any of these
physical traits make them more or less adaptive to climate change?
Reconstructing the thorax was an exercise in starting from scratch,
deliberately trying to avoid being influenced by past theories of how
Neandertals looked or lived, Kramer said.
"Thinking through all the permutations of the different fragments,
it was like a jigsaw without all the pieces. What do the pieces tell
us?" she said. "People have told you it should be a certain way, but you
want to make sure you're not over-reconstructing, or reconstructing it
the way you think it should be. You're trying to maintain a neutral
approach."
Other authors of the study were Daniel Garcia-Martinez of the
National Museum of Natural History and Mikel Arlegi, of the University
of the Basque Country.