Palate Prognathism Relative to Sellion

This is calculated as an index of palate length divided by plate protrusion (relative to sellion) as defined by Rak (1983; see his Plate 34 and Table 3). A prognathic premaxilla is defined by an index greater than 0.57; intermediate prognathism is between 0.30 and 0.57, and weak prognathism is an index less than 0.30. The mean indices for hominin taxa have been taken from Rak (1983). All hominin and extant African ape allocations follow Strait et al. (1997) and Strait & Grine (2001), except for Australopithecus, which has the intermediate condition. While no metric data are available for Kenyanthropus, M.G. Leakey et al. (2001) state that the overall degree of facial prognathism within this species (taking into account post-depositional distortion) is within the range observed in K. rudolfensis. Increased prognathism as observed in Pongo is also defined by increased prognathism with a mean index of 0.71 (n = 21 [see Cameron, 1997b]). While Graecopithecus specimen XIR-1 has been affected by some post-depositional distortion, an index of 0.61 (original specimen) is estimated as a minimum, so it is defined by increased prognathism.

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