A reanalysis of the Taung endocranial surface: Comparison with large samples of living hominids

Abstract

Since its discovery, the natural endocast of the Taung cranium has played a central role in the interpretation of human brain evolution. Aspects of the endocast including the identification of the lunate sulcus, possible expansion of the parietal lobe, and rounded profile suggested to R. Dart that the Taung individual was aligned with humans and not with other anthropoid primates, yet these interpretations were immediately controversial and remain so today. We have generated a detailed curvature map of the Taung endocast to evaluate its surface organization with reference to 189 chimpanzee and 20 human brains. These data enable evolutionary consideration of the surface detail of depressions and projections sufficient to mark primary sulci and variations in sulcal organization due to superficial bridges between adjacent gyri. Our results suggest that the lunate sulcus in the Taung endocast displays a gyral bridge between the occipital lobe and the inferior parietal lobule seen in 65% of our adult human brain hemispheres but in only 1.8% of our chimpanzee ones. The frontal lobe organization of the Taung endocast reflects a superior frontal sulcus pattern seen in 92.8% of our adult human brain hemispheres, but in 0% of our adult chimpanzee sample, and an inferior frontal sulcus pattern seen in 100% of our adult human brain hemispheres but in only 2.1% of our chimpanzee ones. The Taung inferior frontal gyrus retains a fronto-orbital sulcus which is seen in 0% of our adult human brain hemispheres and in 100% of our adult chimpanzee ones. These observations help to resolve some apparent inconsistencies of interpretation of the posterior endocast of the Taung specimen while showing that the specimen shared some derived aspects of endocast organization with humans that were not found in chimpanzees.