Virtual reconstruction of the MH2 pelvis (Australopithecus sediba) and obstetrical implications.

The shape of the pelvis is central for locomotion and obstetrics and thus shows fundamental differences between australopithecines and humans. The presence of derived morphologies in Australopithecus sediba, including a reduced lateral flare of the vertically-oriented iliac blades, a well-developed sigmoid curvature and an anteriorly deflected ASIS, suggested that pelvic reorganization preceded the emergence of bigger-brained babies and modern form of bipedalism. Here, we present a virtual reconstruction of the MH2 pelvis. The tight articulation of the left and right pubic fragments at the symphysis guided the orientation of the midsagittal mirror plane. The fragment of the right pubic basis could then
closely be aligned with the pubic ramus. Finally, the right ilium fragment was fitted in between the pubic basis fragment and the mirror-imaged reconstruction of the MH2 sacrum, using the articulation point at the inferior sacroiliac joint and congruence with the arcuate line. Our reconstruction confirms a more gynaecoid pelvic inlet shape compared to A.L. 288-1, but challenges the presence of other derived features in A. sediba.
Based on this reconstruction we simulated childbirth using 3D-models of minimum and maximum newborn head sizes and shapes predicted by applying a reverse chimpanzee growth curve for DIK-1-1 and Taung. We performed simulations with varying degrees of sacro-iliac joint laxity and different orientations of the fetal head (left occipital anterior, transverse and occipital posterior, thus including the most eutocic and dystocic configurations). Most birth simulations showed eutocic deliveries, suggesting that feto-pelvic constraint
was smaller in MH2 than in extant humans.