This is used here as an important feature relating to masseter muscle leverage; that is, it is implied that the shorter the index, the greater the leverage. This character is defined using the index zygomaticoalveolar height relative to orbitoalveolar height (Kimbel et al., 1984). The results and allocations for the fossil hominins and extant African apes have been taken directly from Strait et al. (1997) and Strait and Grine (2001), while the author generated the indices for Pongo from unpublished data. Most are considered as having a low origin for the master (an index of over 56), which is the primitive condition. Only Pongo with a mean of 57.2 (n = 19), Australopithecus, and species within Paranthropus, are considered to have a high origin (see Strait et al., 1997; Kimbel et al., 1984).
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