The Vertebrae, Ribs, and Sternum of Australopithecus sediba: Special Issue: Australopithecus sediba

Australopithecus sediba is known from two partial skeletons, Malapa Hominins 1 and 2 (MH1 and MH2), a juvenile male and an adult female, respectively. Forty-eight elements of the axial skeleton, including vertebrae, ribs, a sternum, and a sacrum, are known from MH1 and MH2. Here, we describe these ~2.0 Ma fossils and provide raw data and plots of standardized measurements. We revisit the serial positions of the previously described vertebrae and ribs proposed in their initial announcements and provide revised identifications. Additionally, we include in our descriptions and analyses new axial material. Finally, we also test the hypothesis that multiple species are represented in the MH1 and MH2 material and specifically that MH1’s lumbar vertebrae belong to a member of
the genus Homo, whereas those of MH2 belong to Australopithecus. We do not find support for this hypothesis, and instead attribute differences between MH1 and MH2 to their age difference and incomplete growth of the vertebral body in juvenile MH1.