Peter S. Ungar, Frederick E. Grine and Mark F. Teaford

“ Seven specimens examined preserved unobscured antemortem molar microwear. These all show relatively low complexity and anisotropy values. This suggests that none of the individuals consumed especially hard or tough foods in the days before they died. The apparent discrepancy between microwear and functional anatomy is consistent with the idea that P. boisei presents a hominin example of Liem's Paradox, wherein a highly derived morphology need not reflect a specialized diet. ”

“ It has been recently argued, however, that specialized hominin morphology may indicate adaptations for the consumption of occasional fallback foods rather than preferred resources. Dental microwear offers a potential means by which to test this hypothesis in that it reflects actual use rather than genetic adaptation. High microwear surface texture complexity and anisotropy in extant primates can be associated with the consumption of exceptionally hard and tough foods respectively. Here we present the first quantitative analysis of dental microwear for P. boisei. ”

“ While no study to date has focused on dental microwear textures of Paranthropus boisei, its South African congener, Paranthropus robustus has been examined. Although early microwear study hinted at a diet dominated by hard, brittle objects [13] , more recent texture analysis suggests that P. robustus ate such foods only periodically throughout the year [11] . ”

“ Specialists should often reject the very resources that they have evolved traits to use” (p. 223) .
The differences between Paranthropus boisei and P. robustus microwear patterns are more difficult to interpret in this light. Paranthropus robustus has a microwear pattern similar to those of Lophocebus albigena and Cebus apella, two living primates that fall back on hard, brittle foods when less mechanically challenging, preferred resources are unavailable. ”

“ This is notably consistent with Walker's [23] early assertion that P. boisei microwear patterns resemble those of living frugivores, and differ from those of living grazers, leaf browsers, and bone feeders.
Comparisons with the South African hominins suggest that while Paranthropus boisei may have consumed foods with similar ranges of toughness as those eaten by Australopithecus africanus, the eastern African “robust” hominin did not eat harder and brittler foods than the South African “gracile” form. Further, the patterns for P. boisei and P. robustus are very different. ”

“ The idea is that P. robustus “fell back” on less preferred, mechanically challenging items at times of resource stress when preferred foods were unavailable, much like modern-day lowland gorillas do with tough foods. ”

“ Specifically, P. boisei had significantly lower Asfc values and variance than C. apella, and marginally lower Asfc values than L. albigena. Marginally lower is here defined as p≤0.05 for Fisher's LSD but not Tukey's HSD tests. The hominin also had marginally higher Asfc values and lower epLsar values than A. palliata.
The comparisons with other early hominins are even more telling (Fig 2b) . The points on a bivariate plot of Asfc and epLsar for Paranthropus boisei clustered separately from both Australopithecus africanus and P. robustus. ”