Methods of Measurement

In all instances, only a single tooth of any one molar type was included for each individual. Thus, unlike the studies by Suwa et al. (1994, 1996), antimeric values were not averaged. As detailed by Smith (1999), cusp area measurements for the living apes were recorded by placing the individual molars in occlusal view below a Canon Hi8 video camera equipped with a 10x macro lens. Each crown was orientated such that the occlusal crown area was maximized. For the fossil specimens, occlusal photographs of either the original specimens or high definition casts were taken following the same method of crown orientation. This method of orientation is likely equivalent to that of Suwa et al. (1994, 1996), in which the area of the occlusal fovea was maximized to define "horizontal." It differs somewhat from the methods employed by Wood et al. (1983), who used "plane of the cervical line," and Bailey (2004), who used the buccal and distal cervices of upper molars for orientation. Nevertheless, such differences in technique result in only slight differences of cusp area measurement that are comparable to intra-observer error rates using only a single method of measurement (Suwa et al., 1994; Bailey et al., 2004). Indeed, Bailey et al. (2004: 329) concluded that "if certain prescribed standards are employed then cusp and crown base areas measured by different workers can be pooled into a single database." Thus, there is no a priori reason to preclude the data from these different sources being combined.

Measurements of individual cusps followed the procedure established by Wood et al. (1983). Interstitial wear was conservatively corrected, and accessory cusps (e.g., tubercu-lum sextum and tuberculum intermedium) were subdivided, with equal parts being added to the areas of the adjacent principal cusps (Wood et al., 1983; Wood, 1991; Suwa et al., 1994, 1996). Crowns on which any one of the occlusal fissures was completely obliterated were excluded from consideration. Other studies of early hominin molars have emphasized relative cusp proportions (Wood et al., 1983; Wood and Engleman, 1988; Suwa et al., 1994, 1996). However, we utilized raw area measurements, which impart information relating to both size and shape (Stumpf et al., 2002), in addition to relative (scale-free) proportional data. Relative cusp areas were calculated simply by dividing the total occlusal area of each crown by the area of each of its constituent cusps.

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