New Year, New Look: Recent Discoveries Concerning Australopithecus sediba

 

Figure 1: Newly discovered lumbar vertebrae of Australopithecus sediba (Image Credit: Williams et al., 2021)

Paleoanthropologists focus their research on understanding the biological and cultural adaptations of our hominids (early human) ancestors.  Paleoanthropologists are responsible for providing a variety of information concerning who our hominid ancestors were (and were not), as well as how they evolved both biologically and culturally over time.  One popular research question among paleoanthropologists has concerned adaptations from quadrupedal to bipedal locomotion.  Paleoanthropologists have been clear about what specific morphological features were required for bipedal locomotion, but what remains unclear is how long the transition from quadrupedal to bipedal locomotion took place.  Evidence from Ardipithecus ramidus supports the long standing idea that our early human ancestors transitioned from climbing in the trees to bipedal walking, but until recently there was no evidence between Ardipithecus ramidus and Australopithecus afarensis, a full biped, on any additional transitional fossils.  A discovery announced in late November 2021 provides us with more evidence of the locomotion transition, and this blog post will provide you with the information of that discovery.

 

Australopithecus sediba was initially discovered in 2008 by world renowned paleoanthropologist Lee Berger’s son.  The initial discovery near the Malapa Cave site in South Africa yielded two individuals: a juvenile and adult female.  The analysis of the adult female’s remains were incomplete, but they did yield strong evidence that she was mostly arboreally adapted, meaning she spent a lot of time living in the trees.  This was very similarly to Ardipithecus ramidus, who was also arboreal.  The adult female Australopithecus sediba remains demonstrated weak evidence of potential bipedal locomotion, which was found in the knee and ankle bones, but scholars were very reluctant to confirm this species’ bipedal abilities. 

 

That was until the discovery of additional lumbar (lower spine) vertebrae that were discovered adjacent to the original place of discovery (Figure 1).  These lumbar vertebrae were articulated, meaning the bones were found together where they would have existed in the body, and they were matched up to the original adult female Australopithecus sediba specimen.  They matched, leading the new team to conclude that they may have belonged to that individual.  Through extensive reconstructions of the original bones and subsequent rigorous testing it was concluded that the curvature of the spine would have undoubtedly allowed for Australopithecus sediba to bipedally locomote.  This means that much like Ardipethicus ramidus Australopithecus sediba was a transitional species that was both arboreal and bipedal!

 

The team that made this discovery note that this new evidence only confirms the previous evidence, which already reached that conclusion, but their discovery is monumental in doing just that-confirming that which had been previously suspected but not fully realized.  It also provides greater insights into understanding the length of time it took to become fully bipedal, specifically transitioning out of the trees to fully walking on two legs on land.  As Australopithecus sediba is a species that existed between Ardipithecus ramidus and Australopithecus afarensis the timeline and the morphological evolutionary changes are becoming both clearer.

 

Bibliography

Marshall, M. (2021, November 23). New Australopithecus sediba bones suggest extinct hominin was bipedal. New Scientist.

Williams, S. A., Prang, T. C., Meyer, M. R., Nally, T. K., Van Der Merwe, R., Yelverton, C., . . . Ostrofsky, K. R. (2021). New fossils of Australopithecus sediba reveal a nearly complete lower back. eLife.