M Shape

This feature is of functional interest because it relates to tooth crowding of the palate. For instance, an increase in molar breadth may be a requirement to increase its occlusal surface while maintaining reduced palate prognathism. As such, it is also of likely phylogenetic interest. A square tooth is defined by a length/breadth value that is within 5% of both dimensions, with a broad tooth less than 0.95 and a long tooth beyond 1.05 (see Cameron, 1997a). The values for the Miocene hominoids and fossil and extant hominids have been taken from Cameron (1998) unless stated otherwise, while all of the fossil hominin values have been generated from B.A. Wood (1991).

A relatively broad molar (= 0) is observed in Dryopithecus with a mean of 0.93, Graecopithecus with a mean of 0.91 (n = 6 [Koufos, 1995]), Ardipithecus with a mean index of 0.81 (n = 2), and members of the "ana-mensis group" with a mean index of 0.94 (n = 3) (data from Ward et al., 2001), Praeanthropus with a mean value of 0.88, Australopithecus with a mean of 0.90, P boisei specimen OH 5 with an index of 0.82, P robustus with an index of 0.90, H. habilis with a mean index of 0.88, K. rudolfensis with a value of 0.83, H. ergaster specimen KNM-ER 3733 with an index of 0.92, Pongo with a mean index of 0.90 (n = 72), Pan with a mean index of 0.88 (n = 89), and H. sapiens with a mean index of 0.83 (n = 168 to 241, values generated from Thorne, 1976). Square molars (= 1) are observed in Kenyapithecus specimen KNM-FT 46 with an index of 1.02 (Leakey, 1962), Sahelanthropus with an index of 1.02 (Brunet et al., 2002), and Gorilla with a mean index of 0.97 (n = 74).

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