After a 3.3-million-year-old hominin fossil that was found back in 2000 was analyzed, researchers have gotten the most complete spinal column of any early human relative, and now we have a unique snapshot of the crucial transition point where our ancestors evolved towards bipedalism, and according to this, the key segments of the spinal structure emerged millions of years earlier than previously thought.
The bones in question, known as Selam, were discovered in Dikika, on Ethiopia, by Zeresenay Alemseged, a paleoanthropologist at the University of Chicago, during a research expedition. He studied this ancient remains since the discovery, which are odd not only because of its completeness, but also because of its age of death, with just 2.5 years old, making it unique since it’s the earliest and most complete juvenile human ancestor ever discovered.
“Continued and painstaking research on 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”, says Alemseged. “This type of preservation is unprecedented, particularly in a young individual whose vertebrae are not yet fully fused”.
Selam is a member of Australopithecus afarensis, which means she is a relative of the famous fossil discovered on the 1970’s, Lucy, and Selam as many times been nicknamed as ‘Lucy’s Baby’, although she is actually 120 000 years older.
The fossil has been analyzed in this latest study, by using imaging technology at the European Synchrotron Radiation Facility in France, to visualize its missing parts.
“This technology provides the opportunity to virtually examine aspects of the vertebrae otherwise unattainable from the original specimen”, says one of the team members, evolutionary anatomist Fred Spoor from University College London.
When they did it, they found out that the spinal structure occupies a halfway point between living humans and its predecessors, and Selam, like us, had only 12 thoracic vertebrae and 12 pairs of ribs, which is way less than most apes have. We humans, have more vertebrae in our lower back, making it easier for us to walk upright.
Although Selam’s spinal structure exhibits a thoracic-to-lombar joint transition like other human ancestors had, it is the first-time researchers have seen such feature in conjunction with our vertebrae count.
“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”, says one of the team elements, Carol Ward from the University of Missouri. “But we have not been able to determine how many vertebrae our early ancestors had. Selam has provided us the first glimpse into how our early ancestors’ spines were organized”.
The study of this fossil, may help us to better understand how humans actually evolved to walk upright, as we do today.