Summary: A new study reveals portions of the human skeletal structure evolved millions of years earlier than previously believed.
Source: University of Missouri Columbia.
Portions of human skeletal structure were established millions of years earlier than previously thought, Mizzou researcher finds.
For more than 3 million years, Selam lay silent and still. Eager to tell her story, the almost perfect fossil skeleton of a 2 1/2 year-old toddler was discovered at Dikika, Ethiopia — and she had a lot to say. An international research team slowly chipped away at the sandstone surrounding Selam at the National Museums of Ethiopia to reveal something remarkable — even though millions of years have passed, she’s a lot like us. Selam, which means “peace” in the Ethiopian Amharic language, was an early human relative from the species Australopithecus afarensis — the same species as the famous Lucy skeleton. The findings, published this week in the Proceedings of the National Academy of Science, indicate that Selam possesses the most complete spinal column of any early fossil human relative, and her vertebral bones, neck and rib cage are mainly intact. This new research demonstrates that portions of the human skeletal structure were established millions of years earlier than previously thought.
Many features of the human spinal column and rib cage are shared among primates. The human spine reflects the distinctive mode of walking upright on two feet. Among the distinctive features is that humans have fewer rib-bearing vertebrae, bones of the back, than those of our closest relatives, and more vertebrae in the lower back allowing motions for walking effectively. When and how this pattern evolved has been unknown because complete sets of vertebrae are rarely preserved in the fossil record.
“For many years we have known of fragmentary remains of early fossil species that suggest that the shift from rib-bearing, or thoracic, vertebrae to lumbar, or lower back, vertebrae was positioned higher in the spinal column than in living humans, but we have not been able to determine how many vertebrae our early ancestors had,” said Carol Ward, a Curators Distinguished Professor of Pathology and Anatomical Sciences in the MU School of Medicine, and lead author on the study. “Selam has provided us the first glimpse into how our early ancestors’ spines were organized.”
Selam was discovered by Zeresenay Alemseged, a professor in the Department of Organismal Biology and Anatomy at the University of Chicago. The skeleton was surrounded by sandstone, and Alemseged and his team have been preparing the delicate fossil for 13 years at the National Museum of Ethiopia.
“Continued and painstaking research on the Selam shows that the general structure of the human spinal column emerged over 3.3 million years ago, shedding light on one of the hallmarks of human evolution,” Alemseged said. “This type of preservation is unprecedented, particularly in a young individual whose vertebrae are not yet fully fused.”
In order to be analyzed, Selam had to take a trip. She traveled to the European Synchrotron Radiation Facility in Grenoble, France, where Alemseged and the research team used high-resolution imaging technology to visualize the bones. Scans were later sent to Ward at MU for further comparative studies.
“This technology provides the opportunity to virtually examine aspects of the vertebrae otherwise unattainable from the original specimen,” said coauthor of the study Fred Spoor, a professor of evolutionary anatomy in the Department of Biosciences at the University College London.
Ward says the scans indicated that Selam had the distinctive thoracic-to-lumbar joint transition found in other fossil human relatives, but the specimen is the first to show that, like modern humans, our earliest ancestors had only twelve thoracic vertebrae and twelve pairs of ribs, which is fewer than in most apes.
“This unusual early human configuration may be a key in developing more accurate scenarios concerning the evolution of bipedality and modern human body shape,” said Thierra Nalley, an assistant professor of anatomy at Western University of Health Sciences in Pomona, California, also an author of the paper.
About this neuroscience research article
Funding: Funding for the research was provided by Margaret and Will Hearst, the National Science Foundation and the European Synchrotron Radiation Facility. The content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agencies.
Source: Jeff Sossamon – University of Missouri Columbia Image Source: NeuroscienceNews.com image is credited to Zeray Alemseged, University of Chicago. Original Research:Abstract for “Thoracic vertebral count and thoracolumbar transition in Australopithecus afarensis” by Carol V. Ward, Thierra K. Nalley, Fred Spoor, Paul Tafforeau, and Zeresenay Alemseged in PNAS. Published online May 22 2017 doi:10.1073/pnas.1702229114
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]University of Missouri Columbia “3.3 Million Year Old Fossil Reveals the Antiquity of the Human Spine.” NeuroscienceNews. NeuroscienceNews, 22 May 2017. <https://neurosciencenews.com/spine-evolution-6749/>.[/cbtab][cbtab title=”APA”]University of Missouri Columbia (2017, May 22). 3.3 Million Year Old Fossil Reveals the Antiquity of the Human Spine. NeuroscienceNew. Retrieved May 22, 2017 from https://neurosciencenews.com/spine-evolution-6749/[/cbtab][cbtab title=”Chicago”]University of Missouri Columbia “3.3 Million Year Old Fossil Reveals the Antiquity of the Human Spine.” https://neurosciencenews.com/spine-evolution-6749/ (accessed May 22, 2017).[/cbtab][/cbtabs]
Thoracic vertebral count and thoracolumbar transition in Australopithecus afarensis
The evolution of the human pattern of axial segmentation has been the focus of considerable discussion in paleoanthropology. Although several complete lumbar vertebral columns are known for early hominins, to date, no complete cervical or thoracic series has been recovered. Several partial skeletons have revealed that the thoracolumbar transition in early hominins differed from that of most extant apes and humans. Australopithecus africanus, Australopithecus sediba, and Homo erectus all had zygapophyseal facets that shift from thoracic-like to lumbar-like at the penultimate rib-bearing level, rather than the ultimate rib-bearing level, as in most humans and extant African apes. What has not been clear is whether Australopithecus had 12 thoracic vertebrae as in most humans, or 13 as in most African apes, and where the position of the thoracolumbar transitional element was. The discovery, preparation, and synchrotron scanning of the Australopithecus afarensis partial skeleton DIK-1-1, from Dikika, Ethiopia, provides the only known complete hominin cervical and thoracic vertebral column before 60,000 years ago. DIK-1-1 is the only known Australopithecus skeleton to preserve all seven cervical vertebrae and provides evidence for 12 thoracic vertebrae with a transition in facet morphology at the 11th thoracic level. The location of this transition, one segment cranial to the ultimate rib-bearing vertebra, also occurs in all other early hominins and is higher than in most humans or extant apes. At 3.3 million years ago, the DIK-1-1 skeleton is the earliest example of this distinctive and unusual pattern of axial segmentation.
“Thoracic vertebral count and thoracolumbar transition in Australopithecus afarensis” by Carol V. Ward, Thierra K. Nalley, Fred Spoor, Paul Tafforeau, and Zeresenay Alemseged in PNAS. Published online May 22 2017 doi:10.1073/pnas.1702229114