Mandibular Symphysis Orientation

This feature is of developmental interest because it relates to patterns of bone growth and drift within the mandible (see Enlow & Hans, 1996). Symphyseal development probably is also influenced by twisting requirements of this region during mastication (see partly Hylander, 1988). The character states and allocations for the fossil hominins are taken directly from Strait et al. (1997), with one exception, H. sapiens, which is defined here as having a unique pattern, that is, a chin. A receding external symphyseal region (= 0) is observed in Kenyapithecus, Dryopithecus, Graecopithecus, Pongo, Gorilla, Pan, and members of the "anamensis group" (Andrews, 1971; Walker & Andrews, 1973; McCrossin & Benefit, 1997; B. Brown, 1997; C.V. Ward et al., 2001; Begun, 2002). The intermediate condition (= 1) between a receding symphysis and a near-identical symphysis can be observed in Praeanthropus and Australopithecus (Strait et al., 1997). The external mandibular symphyseal orientation is near vertical (= 2) in P. boisei, P. robustus, K. rudolfensis, H. habilis, and H. ergaster (Strait et al., 1997). Homo sapiens is unique in its near vertical orientation with a distinct chin (= 3).

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