Viewpoints: Diet and dietary adaptations in early hominins: The hard food perspective

Abstract

Recent biomechanical analyses examining the feeding adaptations of early hominins have yielded results consistent with the hypothesis that hard foods exerted a selection pressure that influenced the evolution of australopith morphology. However, this hypothesis appears inconsistent with recent reconstructions of early hominin diet based on dental microwear and stable isotopes. Thus, it is likely that either the diets of some australopiths included a high proportion of foods these taxa were poorly adapted to consume (i.e., foods that they would not have processed efficiently), or that aspects of what we thought we knew about the functional morphology of teeth must be wrong. Evaluation of these possibilities requires a recognition that analyses based on microwear, isotopes, finite element modeling, and enamel chips and cracks each test different types of hypotheses and allow different types of inferences. Microwear and isotopic analyses are best suited to reconstructing broad dietary patterns, but are limited in their ability to falsify specific hypotheses about morphological adaptation. Conversely, finite element analysis is a tool for evaluating the mechanical basis of form-function relationships, but says little about the frequency with which specific behaviors were performed or the particular types of food that were consumed. Enamel chip and crack analyses are means of both reconstructing diet and examining biomechanics. We suggest that current evidence is consistent with the hypothesis that certain derived australopith traits are adaptations for consuming hard foods, but that australopiths had generalized diets that could include high proportions of foods that were both compliant and tough.

New model to explain tooth wear with implications for microwear formation and diet reconstruction

“…Recent challenges to the efficacy of microwear as a tool for reconstructing diet center on the notion that "the geometry of microwear features depends critically on the hardness (i.e., resistance to indentation) of microscopic particles in relation to that of enamel," and that phytoliths are not "hard enough to create steep, sharp angled pits or scratches on enamel surfaces" (22). These arguments are based on the innovative nanowear experiments of Lucas et al (19).…”

Dental microwear differences between eastern and southern African fossil bovids and hominins

“…6 This diet-microwear pattern association has been used to infer feeding behaviours of many fossil species, including early hominins. 7 However, a recent study 8 has called into question the efficacy of microwear as a proxy for diet, suggesting that experimental validation is needed to affirm relationships between pattern and foods eaten. For example, in an in vitro wear simulation study, Lucas and coauthors 9 found that while quartz dust on foods can easily wear tooth enamel, phytoliths within them might not.…”

“…This finding has led some to suggest that grit in the environment may be more important to wear pattern than factors intrinsic to items eaten. 10 In fact, Strait et al 8 argued that microwear patterns for early hominins may reflect the dustiness of the environment and, 'say little about the nature of the foods themselves' 8(p.348) . The argument follows that the more striated and less pitted microwear seen for Plio-Pleistocene hominins from eastern Africa than those from southern Africa 7 may have more to do with where they lived than what they ate.…”

“…This possibility has important implications not only for studies of early hominins, but also for the countless other fossil vertebrates for which microwear has been documented and related to diet. 11 Strait et al 8 suggested that quartz dust might cause heavy microwear pitting, and Williams 12 opined that exogenous grit could lead to especially complex surface textures. These suggestions do not explain the lack of such pitting on Paranthropus boisei teeth, which have been suggested to evince extreme macrowear indicative of a gritty, abrasive environment.…”

Dietary variation and food hardness in sooty mangabeys (Cercocebus atys): Implications for fallback foods and dental adaptation

“…The potential significance of fallback foods has been widely embraced by the anthropological community (e.g., Rosenberger, 2013) and is increasingly used to explain dietary variation and interpret masticatory morphology in a variety of extant and extinct primates (e.g., Alba et al, 2010;Chancellor et al, 2012;Daegling et al, 2013;Doran-Sheehy et al, 2009;Etiendem and Tagg, 2013;Grine et al, 2006aGrine et al, , 2006bGrueter et al, 2009;Hanya and Bernard, 2012;Irwin et al, 2014;Laden and Wrangham, 2005;Porter et al, 2009;Strait et al, 2009Strait et al, , 2013Ungar et al, 2008;Vogel et al, 2009;Wright et al, 2009). One feature linked to the fallback food concept is primate molar enamel thickness Lambert et al, 2004).…”