Early Modern Human from Tianyuan Cave, China

Chapter 6 The Tianyuan 1 Mandible

54 C h a p t e r 6 The Tianyuan 1 Mandible THE TIANYUAN 1 mandible is largely complete from the left P4 M1 region, around the symphysis and the right corpus, to the mandibular notch (Figures 6-1 and 6-2). As such, it provides data on the symphyseal region, the lateral corpus, and all of the ramus except the coronoid tip and the condyle. The mandible had been altered as a result of antemortem tooth loss (Chapters 5 and 12), but it appears that the associated pathological alterations were limited to the alveolar process. The changes primarily affected the left corpus, and as a result the morphological assessment of the corpus employs only the symphyseal region and the right side. Both I1 s were lost antemortem, and their sockets completely closed over; therefore in the assessment of the symphysis, the original alveolar bone was estimated using the preserved labial and lingual contours and the level of the alveolar plane at the right I1 I2 and I2 C1 interdental septa. The alveolar bone changes associated with the extensive wear of the molars and the supereruption of the right molars, and especially the right M3 (Chapters 5 and 12), appear to have affected only the alveolar margin and not the underlying corpus, and those alveolar changes are taken into account in the assessment of the lateral corpus and anterior ramus. The extensive interproximal wear of the teeth almost certainly produced mesial drift of the dentition, such that the more distal teeth may well be farther mesial than they would have been when they were all first erupted in the late 2nd decade of life. This would have mainly affected the perceived positions of the mental foramen relative to the dentition, the possibility of a retromolar space, and to a lesser extent the exact positions of corpus heights and breadths taken relative to the dentition. The overall effect of these changes should be minimal. THE TIANYUAN 1 MANDIBLE 55 Overall Size and Dimensions Despite the postmortem damage to the Tianyuan 1 mandible, it is possible to estimate reliably its overall length and, through mirror imaging, its dental arcade breadth. Mandibular breadths across the condyles and gonion are less reliable , given the complete absence of the condyle and lack of knowledge of its posiFigure 6-1. Superior (above) and inferior (below) views of the Tianyuan 1 mandible. Scale in centimeters. CHAPTER 6 56 tion relative to the mandibular notch crest and given the trigonometric effects of being farther from the symphysis. Moreover, reliable bigonial and/or bicondylar breadths are rare in the fossil record, given ramal damage and/or distortion along the mandible. The estimated superior mandible length (midsagittal distance from the midFigure 6-2. Lateral (top) and medial (bottom) views of the Tianyuan 1 mandible. Lateral view is in norma lateralis (perpendicular to the sagittal plane); medial view is an oblique one perpendicular to the lateral corpus. Scale in centimeters. THE TIANYUAN 1 MANDIBLE 57 condyles to infradentale) of Tianyuan 1 (Table 6-1) of ~98 mm is relatively small (Table 6-2). It is slightly below the smallest Neandertal value (Regourdou 1 at 100 mm; although La Naulette 1 was probably smaller), and it is below the three available Middle Paleolithic modern human (MPMH) values and the two western Early Upper Paleolithic (EUP) lengths. It is nonetheless well within the ranges of variation of the western Mid Upper Paleolithic (MUP) sample and the eastern Asian early modern human sample, falling slightly below Minatogawa 1 and ZKD-UC 101 and slightly above ZKD-UC 104. It is in the middle of recent human sample distributions (Trinkaus, 2003). At the same time, the dental arcade breadth of ~64.5 mm is modest but unexceptional for a Late Pleistocene human. It is essentially on the means of the western early modern human samples, but it is moderately low for a Neandertal or for an eastern Asian early modern human (Table 6-2). It remains within the ranges of variation of all of the comparative samples. The minimum ramus breadth of Tianyuan 1 of 39.5 mm (Tables 6-1 and 6-2) is small compared to the two Middle Paleolithic samples and especially relative to the very high values for the EUP Nazlet Khater 2 and Oase 1 mandibles. Nonetheless , three of the Neandertals have small ramus breadths; it is small for Muierii 1 (Soficaru et al., 2006), and they...