Mandibular Corpus Robusticity Breadth Height

This character measures the robusticity of the corpus at M2. This feature is of functional and developmental interests because it relates to bone deposition associated with tensile and compressive stress during the masticatory cycle (see Hylander, 1984, 1988; Hylander & Johnson, 1994; Hylander et al., 2000; B. Brown, 1997). All data for the hominins has been taken from B.A. Wood (1991), while all extant hominid data is from DWC (unpublished). Most of the values for the Miocene hominids have been taken from Begun (1994b). The mean hominid index for this character is 0.56 (n = 103), with one standard deviation equal to 0.08. Thus, the intermediate condition is defined by values between 0.48 and 0.64. The minimum extant hominid value is 0.38, and the maximum extant value is 0.75. Note, while Begun (1994b) gives values for Kenyapithecus, the specimens used to define this genus (from Maboko Island) have since been reallocated to Equatorius (see Ward et al., 1999).

Intermediate corpus robusticity (= 0) is seen in Kenyapithecus with a mean index of 0.55 (taken from M1 [Andrews, 1971]), Dryopithecus with a mean index of 0.64 (n = 7), Pongo with a mean index of 0.57 (n = 18), Gorilla with a mean index of 0.56 (n = 22), Pan with a mean index of 0.55 (n = 63), and H. sapiens with a mean index of 0.56 (n = 8). While no data were available for the corpus at M2 for members of the "anamensis group," specimen KNM-KP 29281 has a robusticity of 0.58 from the P4/M1 junction (data taken from C.V. Ward et al., 2001). Also, Strait and Grine (2001) allocate the "anamensis group" to the same condition observed in H. sapiens and Pan. Thus, this group is defined here by having the intermediate condition. A relatively robust corpus (= 1) is observed in Graecopithecus with a mean index of 0.66 (n = 3), Praeanthropus with a mean index of 0.71 (n = 7), H. habilis with a mean index of 0.71 (n = 3), and K. rudolfensis with a mean index of 0.70 (n = 3). An extremely robust corpus (= 2) is observed in Australopithecus with a mean index of 0.76 (n = 5), P. boisei with a mean index of 0.78 (n = 22), and P. robustus with a mean index of 0.79 (n = 4).

0 0

Post a comment