Facial Dishing

This character is of functional and developmental interest because it relates to masseter muscle development, mid-facial prognathism, as well as patterns of bone growth within this area. This character is also defined by the morphological pattern originally noted by Robinson (1962). Robinson defined facial dishing as a result of the expanded and anteriorly positioned zygomatic prominence, relative to the more posterior "sunken" nasal aperture and infraorbital plane (see also Tobias, 1967; Rak, 1983). Using this morphological pattern, four conditions are recognized: absent (a developed premaxilla; i.e, prognathic to varying degrees, which negates the formation of mid-facial depression) (= 0); lateral and upper face near vertical and mid-face concave (= 1); the whole facial region is strongly convex (= 2); and facial dishing as defined by Robinson is present (= 3).

A developed mid-face-premaxilla (= 0) is observed in Dryopithecus, Gorilla, Pan, Sahelanthropus, both species of Kenyanthropus, Praeanthropus, Australopithecus, the "garhi group," and species of Homo. Shallow mid and lateral upper facial dishing defines Pongo (= 1). The condition in Graecopithecus is unique because it is marked by strong convexity and a mid-face that is more prognathic relative to Pongo, but it also lacks the "snout-like" appearance seen in the African hominids (= 2) (Cameron 1997a; partly de Bonis & Koufos, 1993). Facial dishing as described by Robinson (1962) is observed only within species of Paranthropus (= 3) (Asfaw et al., 1999; Skelton et al., 1986; Skelton & McHenry, 1992).

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