Commonalities in dimorphism and variability in the anthropoid pelvis, with implications for the fossil record

Abstract

This study identifies commonalities in dimorphism and variability of the true pelvis in seven anthropoid species. The results are discussed in terms of selection and obstetrics, and the results are applied in an analysis of the australopithecine pelvis. Pongids and humans share a common pattern of pelvic dimorphism that is independent of obstetric relationships. The inference is that this pattern of pelvic dimorphism also characterized extinct pongids and hominids. Commonalities in pelvic variability are identified and are discussed within the context of phenotypic varability and selection intensity. The results show that circumferences of the pelvic planes are of low variability, whereas the shapes of the pelvic planes are highly variable. The inference is that selection on the true pelvis is principally associated with providing adequate potential space for the fetus, whereas pelvic shape is less important. For the measures of low variability, pelvimetrics from a single fossil specimen can be regarded as being generally representative for the species. With these results, the australopithecine pelvis is examined. Relative to estimated newborn brain size, the australopithecine pelvis was potentially more spacious than that in humans. The spacious pelvic inlet in Australopithecus is due to a long pubis and broad sacrum. However, selection for a long pubis and broad sacrum in Australopithecus was not related to obstetrics.