Auditory Meatus

This character defines the relative position of the inferior tympanic edge relative to porion. This feature can be partially related to the length of the auditory tube, lateral expansion of the cranial base, lateral inflation of the mastoid process, and the development of the supramastoid crest. It is difficult to disentangle this feature from a number of functional and developmental processes, and it is for this reason that it is maintained as a separate feature.

The condition observed in Pongo, Pan, Sahelanthropus, the "anamensis group", Praeanthropus, Australopithecus, P. walkeri, both species of Kenyanthropus, H. ergaster, and H. sapiens is defined by a tympanic edge that is medially positioned, relative to porion (= 0) (see Kimbel et al., 1994; M.G. Leakey et al., 1995; Strait et al., 1997; Strait & Grine, 1998, 2001; M.G. Leakey et al., 2001; Brunet et al., 2002). The condition observed in Gorilla, Ardipithecus, P. boisei, P. robustus, and H. habilis is for the tympanic to be laterally placed relative to porion (= 1) (see B. Brown et al., 1993; T.D. White et al., 1994; Strait & Grine, 2001; Strait et al., 1997). Because the South African specimens of H. habilis are not considered here, and because the inferior tympanic edge is laterally placed in the east African H. habilis specimen KNM-ER 1805 (Strait & Grine, 1998; Strait et al., 1997), H. habilis is allocated as displaying the derived condition.

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