A Homo erectus calvarium [Sambungmacan 4 (Sm 4)] was recovered from Pleistocene sediments at Sambungmacan in central Java. Micro–computed tomography analysis shows a modern human–like cranial base flexion associated with a low platycephalic vault, implying that the evolution of human cranial globularity was independent of cranial base flexion. The overall morphology of Sm 4 is intermediate between that of earlier and later Javanese Homo erectus ; apparent morphological specializations are more strongly expressed in the latter. This supports the hypothesis that later Pleistocene Javanese populations were substantially isolated and made minimal contributions to the ancestry of modern humans.