This character state is defined by an index of minimum frontal breadth (just posterior to the supraorbital torus) divided by maximum upper facial breadth (bi-frontomalare temporale). The extant hominids have a mean index value of 0.66, with one standard deviation of 0.08 (n = 122). This gives an intermediate range of 0.58-0.74. Thus, any value below 0.58 suggests increased postorbital constriction, while any value above 0.74 is reduced. The minimum extant hominid value is 0.46 and the maximum value is 0.80.
Increased postorbital constriction (= 0) is observed in Gorilla, with a mean value of 0.57 (n = 36), P walkeri (KNM-WT 17000) with a value of 0.57, and P. boisei (KNM-ER 406), also with an index of 0.57. The intermediate condition (= 1) is observed in Dryopithecus specimen RUD 77 (original), with an estimated index of 0.73, Sahelanthropus specimen TM 266-01-060-1 with an index of 0.59 (data from Brunet et al., 2002), Australopithecus with a mean index of 0.66 (Kimbel et al., 1984), P robustus with a mean index of 0.70 (data from B.A. Wood, 1991), H. habilis (OH 24 & KNM-ER 1813) with a mean index of 0.72, K. rudolfensis with a mean index of 0.70, H. ergaster with a mean index of 0.75 (data from B.A. Wood, 1991), Pongo with a mean index of 0.66 (n = 22), and Pan with a mean index of 0.70 (n = 64). While no data is available for the "garhi group," it is said to be similar to that observed in Australopithecus (Asfaw et al., 1999; Strait & Grine, 2001). Also, while no raw data is available for K. platyops, postorbital constriction is said to be similar to that of the "1470 group" (K. rudolfensis); thus, it is considered to be within the range of Pan and Pongo (see Lieberman, 2001). Reduced postorbital constriction (= 2) is observed in Praeanthropus with an index of 0.80. Absolutely reduced postorbital constriction (= 3) is observed in H. sapiens with a mean index of 0.92 (n = 168 [data from Thome, 1976]).
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