Upper Incisor Reduction II Area Orbital Area

Incisor size is usually related to dietary considerations and is thus of functional and phylogenetic interest (see Ungar & Kay, 1995; Kay & Ungar, 1997; Ungar, 2002). The index used here is the sum of I1 and I2 mesial-distal length divided by orbital area. All data for fossil hominins has been taken from Wood (1991). The mean for the extant hominids is 0.14 (n = 92) with one standard deviation of 0.03. This gives an intermediate range of 0.11-0.17. The minimum extant hominid value is 0.08 and maximum is 0.23.

Increased incisor area (= 0) is observed in Pongo with a mean index of 0.18 (n = 18). The intermediate condition (= 1) is observed in Graecopithecus specimen XIR-1 (original) with an index of 0.15, Australopithecus with a mean index of 0.13, P. robustus with a mean index of 0.12, H. habilis with a mean index of 0.13, Gorilla with a mean index of 0.12 (n = 23), Pan with a mean index of 0.13 (n = 51), and H. sapiens with a mean index of 0.12 (data from Thorne, 1976). The broad incisor alveolar border in P. walkeri specimen KNM-WT 17000 suggests that the incisors were probably within the range of Gorilla. While no data is available for Ardipithecus, the "anamensis group," Praeanthropus, and members of the "garhi group," they are said to be similar to either Australopithecus or early Homo, which are allocated here to the intermediate condition (Asfaw et al., 1999; Strait & Grine, 2001). Reduced incisor size (= 2) is observed in P. boisei specimen OH 5 with an index of 0.10.

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