The occipital torus and developmental age of Sangiran-3.

Abstract

Since its discovery in 1938 Sangiran-3 has been considered a juvenile Pithecanthropus (Homo) erectus, and therefore, excluded from studies of adult H. erectus. Although morphological features align Sangiran-3 with H. erectus, its age designation rests on an unconvincing reconstruction of the occipital torus and lack of sutural fusion. Evaluation of the occipital shows the original reconstruction is faulty and that the current midline occipital torus is actually the right lateral torus. The new reconstruction of Sangiran-3 results in midline toral morphology and development that is comparable with that in Sangiran-2. Compared with juvenile and adult H. erectus and Homo sapiens Sangiran-3 has three fully developed layers of vault bone with localized hypertrophy of the outer table into a sagittal keel, bregmatic eminence, and occipital torus. Sangiran-3's absolute vault thickness is also within the range of adult H. erectus. In addition, the coronal suture is fully interdigitated and sagittal sutural complexity is consistent with adult H. erectus. Sangiran-3's parietal sagittal contours are indistinguishable from adult H. erectus, whereas sagittal vault contours of juvenile H. erectus are usually more rounded than adults. These features indicate that Sangiran-3 is best considered a young adult H. erectus and should be included in metric and non-metric analyses of this taxon.