A new study ends a decades-old debate about how early hominins moved.
Australopithecus sediba was first described as an extinct human relative in 2010. It was a small hominin that lived about 2 million years ago. Thanks to the examination of the fossil lumbar vertebrae, a team of international paleoanthropologists, led by the University of New York and the University of the Witwatersrand in Johannesburg, has concluded that Australopithecus sediba would have had an upright posture and would have walked comfortably on two legs; however, other aspects of bone shape suggest that, in addition to walking, this hominin also spent a significant amount of time climbing trees.
A bipedal species part of the time
The bones were discovered in the Malapa cave system northwest of Johannesburg, South Africa (World Heritage Site), and the first analysis determined that they were a male child, christened Karabo and an adult female, named Issa (who means “protector” in Swahili). Together with previously discovered vertebrae, they form one of the most complete lower vertebrae ever discovered in the early hominin record and give insight into how this ancient human relative walked and climbed.
“The lumbar region is critical to understanding the nature of bipedalism in our earliest ancestors and to understanding how well adapted they were to walking on two legs,” says Scott Williams of New York University and Wits University and lead author of the Article. “Associated series of lumbar vertebrae are extraordinarily rare in the hominin fossil record, and only three comparable lower spines are actually known from the entire early African record.”
Hominid in transition
After joining the vertebrae together, the team concluded that his spine was curved so that, when viewed from the side, it forms a smooth S-shape, a characteristic of humans that keeps the body mass centered over the pelvis for a efficient biped walk. But clear upper body adaptations had also been found for climbing trees.
While Issa was already one of the most complete skeletons of an ancient hominin ever discovered, these vertebrae practically complete the lower back and make Issa’s lumbar region a competitor for not just the lower back of the hominin. best-preserved ever discovered, but also probably the best-preserved , the authors note.
Previous studies of this ancient species had highlighted mixed adaptations across the skeleton in sediba that have indicated its transitional nature between walking like a human and climbing like an ape.
The study concludes that sediba is a transitional form of an ancient human relative , and its spine is clearly intermediate in shape between modern humans (and Neanderthals) and great apes.
Referencia: Scott A Williams, Thomas Cody Prang, Marc R Meyer, Thierra K Nalley, Renier Van Der Merwe, Christopher Yelverton, Daniel García-Martínez, Gabrielle A Russo, Kelly R Ostrofsky, Jeffrey Spear, Jennifer Eyre, Mark Grabowski, Shahed Nalla, Markus Bastir, Peter Schmid, Steven E Churchill, Lee R Berger. New fossils of Australopithecus sediba reveal a nearly complete lower back. eLife, 2021; 10 DOI: 10.7554/eLife.70447