New fossils of Australopithecus Sediba reveal a nearly complete lower back

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

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba. We show that MH2 possessed a lower back consistent with lumbar lordosis and other adaptations to bipedalism, including an increase in the width of intervertebral articular facets from the upper to lower lumbar column (‘pyramidal configuration’). These results contrast with some recent work on lordosis in fossil hominins, where MH2 was argued to demonstrate no appreciable lordosis (‘hypolordosis’) similar to Neandertals. Our three-dimensional geometric morphometric (3D GM) analyses show that MH2’s nearly complete middle lumbar vertebra is human-like in overall shape but its vertebral body is somewhat intermediate in shape between modern humans and great apes. Additionally, it bears long, cranially and ventrally oriented costal (transverse) processes, implying powerful trunk musculature. We interpret this combination of features to indicate that A. sediba used its lower back in both bipedal and arboreal positional behaviors, as previously suggested based on multiple lines of evidence from other parts of the skeleton and reconstructed paleobiology of A. sediba.

    Original languageEnglish (US)
    Article numbere70447
    JournaleLife
    Volume10
    DOIs
    StatePublished - 2021

    Keywords

    • Animals
    • Back/anatomy & histology
    • Female
    • Fossils/anatomy & histology
    • Hominidae/anatomy & histology
    • Locomotion
    • Posture

    ASJC Scopus subject areas

    • Biochemistry, Genetics and Molecular Biology(all)
    • Immunology and Microbiology(all)
    • Neuroscience(all)

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