First virtual reconstructions of the frontal lobe and temporal pole of the Taung (Australopithecus africanus) endocast

Abstract : The Taung type specimen for Australopithecus africanus includes a natural endocast that reproduces external morphology of a large portion of the right cerebral hemisphere, and a separate fragment of the fossilized face that articulates with the endocast. The natural endocast lacks the right temporal pole and rostral part of the frontal lobes, which were embedded in the back of the facial fragment. Although these structures have previously been reconstructed manually using the external morphology of the facial fragment as a guide, we used advanced 3D-CT technology to prepare virtual reconstructions of the frontal lobes and right temporal pole. We then joined these parts of Taung's virtual endocast to a virtual image of the natural endocast, and reconstructed the remaining missing areas using mirror imaging. The resulting virtual endocast of Taung was compared with 3D geometrical models of chimpanzee and bonobo endocasts reconstructed from CT scans of dry skulls representing individuals at the same dental developmental age as Taung. We employed recently developed automated computational tools that allowed processing of 3D free-form surfaces and quantification of the mean anatomy within each species (chimpanzees and bonobos) as well as the pattern of variability around these means. These results were compared to those for Taung, and allowed us to test Raymond Dart's hypothesis that Taung's brain was advanced toward a human condition in the shape of its prefrontal as well as parieto-occipital association cortices. Our findings lend strength to Dart's suggestion that australopithecine brains evolved in a global rather than mosaic manner.