Discussions on the Significance and Geologic Age of Penghu 1 Mandible
WU Xinzhi, TONG Haowen
2015, 34(03):
281-287.
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This human mandible has been reported by Chang et al. in Nature Communications, 2015. The present authors consider that it is worthy to give further analysis and discussion on the significance and date of this important specimen. The extraordinarily high index of robustness, large bicondylar breadth, large P1-P2 alveolar length, robust lateral superior torus, wide extramolar sulcus, especially big molar and absence of the mental protuberance, suggest the mandible belonging to Middle Pleistocene. While the alveolar index at M2, superior mandibular length and ramus heights may represent the progressive features of this mandible. The positions of the lateral prominence and mental foramen, the deep depression formed on the planum triangulaire between the crista endocoronoidea and the crista endocondyloidea, congenital agenesis of the third molar, absence of the retromolar space, short condyle and large M2 indicate the mandible’s closer affinity with the East Asian than with European Pleistocene humans. The lack of typical member of Stegodon-Ailuropoda fauna in Penghu fauna suggest that the Penghu mandible was more probably derived from northern than southern China. The single mental foramen and wide extramolar sulcus suggest this mandible not belonging to Homo erectus. The authors incline to tentatively classify the mandible into archaic Homo sapiens without excluding the possibility of raising a new species name for it after discovering relevant fossils in the future. If the the standard for sexing in Homo erectus proposed by Weidenreich could be applied to the Penghu mandible, it is reasonable to be of a female individual. Among human fossils the lack of chin could be seen in Neanderthals, Middle Plesistocene and earlier humans. The absence of retromolar space, congenital agenesis of third molar, and the position of the mental foramen, wide extramolar sulcus, and the alveolar index at M2 are unfavourable to attribute the Penghu mandible to Neanderthals. The index of robustness, P1-P2 alveolar length, condyle length, the position of lateral prominence support the Penghu mandible being closer to Middle Pleistocene Homo of East Asia than to Neanderthals. So the lack of chin in Penghu mandible more probably reflex its Middle Pleistocene age than its attributing to the Neanderthal lineage. Until present mandibles with incipient chin have been found at Klasies River Mouth of South Africa and Zhirendong Cave, Chongzuo, South China. The former is estimated as around 90 ka BP, the latter was dated as around 110 ka BP. Penghu mandible has no chin at all, so it could not be as late as the mandibles of these two sites or it should be in Middle Pleistocene. The sea bottom of Penghu channel was exposed in several time periods including 10ka~70ka, 130ka~190ka, 225ka, 240ka~280ka, (300ka?,) 335ka~360ka and 425ka~450ka BP. Judging from the dates of exposures of sea bottom in this area of Taiwan Strait and morphology of the Penghu mandible especially the difference between Penghu and Zhirendong mandibles in the morphology of symphyseal region, the date of the former could be in the range between 130 ka and 450 ka BP.
