Gamma-ray spectrometric dating of late Homo erectus skulls from Ngandong and Sambungmacan, Central Java, Indonesia.

Hominid fossils from Ngandong and Sambungmacan, Central Java, Indonesia, are considered to be the most anatomically derived and youngest representatives of Homo erectus. Nondestructive gamma-ray spectrometric dating of three of these Homo erectus skulls showed that all samples underwent uranium leaching. Nevertheless, we could establish minimum age estimates of around 40ka, with an upper age limit of around 60 to 70ka. This means that the Homo erectus of Java very likely survived the Toba eruption and may have been contemporaneous with the earliest Homo sapiens in Southeast Asia and Australasia.

Cranial morphology of Javanese Homo erectus: new evidence for continuous evolution, specialization, and terminal extinction.

Our current knowledge of the evolution of Homo during the early to middle Pleistocene is far from complete. This is not only because of the small number of fossil samples available, but also due to the scarcity of standardized datasets which are reliable in terms of landmark identification, interobserver error, and other distorting factors. This study aims to accurately describe the cranial morphological changes of H. erectus in Java using a standardized set of measurements taken by the authors from 18 adult crania from Sangiran, Trinil, Sambungmacan, and Ngandong. The identification of some obscure landmarks was aided by the use of micro-CT imaging. While recent studies tend to emphasize evolutionary conservatism in Javanese H. erectus, our results reinforce the theory that chronologically later groups experienced distinct morphological changes in a number of cranial traits. Some of these changes, particularly those related to brain size expansion, are similar to those observed for the genus Homo as a whole, whereas others are apparently unique specializations restricted to Javanese H. erectus. Such morphological specializations in Java include previously undescribed anteroposterior lengthening of the midcranial base and an anterior shift of the posterior temporal muscle, which might have influenced the morphology of the angular torus and supramastoid sulcus. Analyses of morphological variation indicate that the three crania from Sambungmacan variously fill the morphological gap between the chronologically earlier (Bapang-AG, Bapang Formation above the Grenzbank zone in Sangiran) and later (Ngandong) morphotypes of Java. At least one of the Bapang-AG crania, Sangiran 17, also exhibits a few characteristics which potentially indicate evolution toward the Ngandong condition. These strongly suggest the continuous, gradual morphological evolution of Javanese H. erectus from the Bapang-AG to Ngandong periods. The development of some unique features in later Javanese H. erectus supports the hypothesis that this Javanese lineage went extinct without making significant contributions to the ancestry of modern humans.

Internal cranial features of the Mojokerto child fossil (East Java, Indonesia).

The island of Java, Indonesia, has produced a remarkable number of fossil hominid remains. One of the earliest specimens was found in Perning and consists of an almost complete calvaria belonging to a juvenile individual, known as the Mojokerto child (Perning I). Using computed tomography, this study details its endocranial features. The specimen is still filled with sediment, but its inner surface is well preserved, and we were able to reconstruct its endocranial features electronically. The Mojokerto endocast is the only cerebral evidence available for such a young Homo erectus individual. We provide an analytical description, make comparisons with endocasts of other fossil hominids and modern humans, and discuss its individual age and taxonomic affinities. The ontogenetic pattern indicated by the Mojokerto child suggests that the growth and development of the Homo erectus brain was different from that of modern humans. The earliest stages of development, as characterized by this individual, correspond to important supero-inferior expansion, and relative rounding of the cerebrum. The following stages differ from that of modern humans by marked antero-posterior flattening of the brain and particularly antero-posterior development of the frontal lobes, resulting in the adult H. erectus morphology.

Taxonomic affinities and evolutionary history of the Early Pleistocene hominids of Java: dentognathic evidence.

Temporal changes, within-group variation, and phylogenetic positions of the Early Pleistocene Javanese hominids remain unclear. Recent debate focused on the age of the oldest Javanese hominids, but the argument so far includes little morphological basis for the fossils. To approach these questions, we analyzed a comprehensive dentognathic sample from Sangiran, which includes most of the existing hominid mandibles and teeth from the Early Pleistocene of Java. The sample was divided into chronologically younger and older groups. We examined morphological differences between these chronological groups, and investigated their affinities with other hominid groups from Africa and Eurasia. The results indicated that 1) there are remarkable morphological differences between the chronologically younger and older groups of Java, 2) the chronologically younger group is morphologically advanced, showing a similar degree of dentognathic reduction to that of Middle Pleistocene Chinese H. erectus, and 3) the chronologically older group exhibits some features that are equally primitive as or more primitive than early H. erectus of Africa. These findings suggest that the evolutionary history of early Javanese H. erectus was more dynamic than previously thought. Coupled with recent discoveries of the earliest form of H. erectus from Dmanisi, Georgia, the primitive aspects of the oldest Javanese hominid remains suggest that hominid groups prior to the grade of ca. 1.8-1.5 Ma African early H. erectus dispersed into eastern Eurasia during the earlier Early Pleistocene, although the age of the Javanese hominids themselves is yet to be resolved. Subsequent periods of the Early Pleistocene witnessed remarkable changes in the Javanese hominid record, which are ascribed either to significant in situ evolution or replacement of populations.

Homo erectus calvarium from the Pleistocene of Java.

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.