A team of scientists has pieced together how the hominin Australopithecus sediba (Au. sediba) walked, chewed, and moved nearly two million years ago. Their research, which appeared as six papers in the journal Science, also shows that Au. sediba had a notable feature that differed from that of modern humans—a functionally longer and more flexible lower back.
Together, the studies offer a comprehensive depiction of some of the most complete early human ancestral remains ever discovered.
Since its discovery in August 2008, the site of Malapa—located about 30 miles northwest of Johannesburg—has yielded more than 220 bones of early hominins representing more than five individuals, including the remains of babies, juveniles, and adults. The evidence published in Science is based on two individuals from the site. The fossils from the site are 1.977 to 1.98 million years in age.
“The abundance and remarkable preservation of fossils from Malapa provide unique insights into the way this fascinating extinct species interacted with and moved around in its environment,” says NYU anthropologist Scott Williams, the lead author of one of the six papers.
Williams, part of NYU’s Center for the Study of Human Origins, and his colleagues authored a paper describing Au. sediba’s vertebral column. The work is the first to analyze elements of its cervical, thoracic, lumbar, and sacral regions. Their analysis was based on partially complete spines of the two Au. sediba skeletons.
Their study reveals that Au. sediba had a human-like curvature of the lower back, but this was functionally longer and more flexible than that of modern humans.
“They probably walked in a way that we might find strange—a compromise form of bipedalism indicative of a hominin that still partially relied on climbing trees,” Williams explains.
He notes that “the adult female is the first early hominin skeleton that preserves an intact terminal thoracic region and this provides critical information on the transition in inter-vertebral joints, and, by inference, mobility of the lower back.
“The bony spine of Au. sediba likely had the same number of vertebrae as that of modern humans,” Williams adds. “However, it differed in one primary aspect of its configuration—the transition in inter-vertebral articular facets occurred at a higher level of the spine than normally occurs in modern humans. In combination with other features, a functionally longer lower back would have allowed for a more flexible spine in Au. sediba relative to that of modern humans.”
In addition, morphological indicators of strong lumbar curvature suggest that Au. sediba evolved in this regard relative to Au. africanus, which lived between 3.03 and 2.04 million years ago, and closer to the more recent Nariokotome Homo erectus skeleton—to date, the most complete early human skeleton discovered.
The research was conducted at the Evolutionary Studies Institute at the University of the Witwatersrand in South Africa, where Au. sediba’s remains were discovered.