Upper Second Molar Area Orbital Area

This character gives a relative statement of the molar complex as defined by the M2 area (divided by orbital area). Combined with the previous character, we can determine whether any identified changes in the premolar/ molar complex are the result of increased molar size or reduced premolar size. That is, the previous character on its own does not enable us to determine whether the premolar complex has increased or reduced in size. All data to generate the fossil hominin has been taken from B.A. Wood (1991) unless stated otherwise. The extant hominid mean value is 0.11 (n = 124), with one standard deviation of 0.03. The intermediate range is between 0.08 and 0.14. The minimum extant hominid value was 0.06 and the maximum value was 0.18.

A reduced molar complex (= 0) is observed in Dryopithecus specimen RUD 77 with an estimated index of 0.11 (data from Kordos, 1988), Sahelanthropus specimen TM266-01-060-1 with an index of 0.13 (data from Brunet et al., 2002), H. ergaster specimen KNM-ER 3733 with an index of 0.12, Pongo with a mean index of 0.12 (n = 22), Gorilla with a mean index of 0.13 (n = 36), Pan with a mean index of 0.09 (n = 66), and H. sapiens with a mean index of 0.13 (values generated from Thorne, 1976). While no data are available for Kenyanthropus, M.G. Leakey et al. (2001; see also their Figure 3a) state that it has among the smallest M2 relative to all other Pliocene hominins. A large molar complex (= 1) is observed only in H. habilis with a mean index of 0.18. An extremely large molar complex (= 2) is observed in Graecopithecus specimen XIR-1 (original) with an index of 0.23, Australopithecus with a mean index of 0.21, P. boisei specimen OH 5 with an index of 0.27, P. robustus with a mean value of 0.23, and the "1470 group" with a mean index of 0.20. While no values could be generated using this index for either Praeanthropus or the "garhi group," Asfaw et al. (1999) demonstrate that Praeanthropus and specimen B0U-VP-12/130 (the "garhi group") are within the size range of both Australopithecus and K. rudolfensis. This also applies to Ardipithecus and members of the "anamensis group" because M.G. Leakey et al. (2001) show that both groups in overall area are within the range observed in Praeanthropus, Australopithecus, and K. rudolfensis. Finally, while no upper molars are available for P walkeri, the massive tooth roots observed in KNM-WT 17000 clearly indicate that the molars were extremely large.

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