Viewpoints: Feeding mechanics, diet, and dietary adaptations in early hominins

Abstract

Inference of feeding adaptation in extinct species is challenging, and reconstructions of the paleobiology of our ancestors have utilized an array of analytical approaches. Comparative anatomy and finite element analysis assist in bracketing the range of capabilities in taxa, while microwear and isotopic analyses give glimpses of individual behavior in the past. These myriad approaches have limitations, but each contributes incrementally toward the recognition of adaptation in the hominin fossil record. Microwear and stable isotope analysis together suggest that australopiths are not united by a single, increasingly specialized dietary adaptation. Their traditional (i.e., morphological) characterization as "nutcrackers" may only apply to a single taxon, Paranthropus robustus. These inferences can be rejected if interpretation of microwear and isotopic data can be shown to be misguided or altogether erroneous. Alternatively, if these sources of inference are valid, it merely indicates that there are phylogenetic and developmental constraints on morphology. Inherently, finite element analysis is limited in its ability to identify adaptation in paleobiological contexts. Its application to the hominin fossil record to date demonstrates only that under similar loading conditions, the form of the stress field in the australopith facial skeleton differs from that in living primates. This observation, by itself, does not reveal feeding adaptation. Ontogenetic studies indicate that functional and evolutionary adaptation need not be conceptually isolated phenomena. Such a perspective helps to inject consideration of mechanobiological principles of bone formation into paleontological inferences. Finite element analysis must employ such principles to become an effective research tool in this context. Am J Phys Anthropol 151:356-371, 2013. V C 2013 Wiley Periodicals, Inc.

Testing Dietary Hypotheses of East African Hominines Using Buccal Dental Microwear Data

“…It also depends on the mechanical energy attributable to particles, especially their speed, while moving between the cheek and the buccal enamel surfaces of teeth during food chewing. As has been acknowledged, the precise causes of microwear formation are difficult to "pin down" and involve mechanics that are more complex than imagined [118]. More specific research on enamel etching, analyzing both forces and particle speed, are yet required.…”

“…The occlusal microwear pattern of A . afarensis have suggested that Gorilla and/or Theropithecus constitute the best modern analogues for dietary preference of this species, and that there is no occlusal microwear evidence of the mastication of hard, brittle items [118]. The buccal microwear pattern of A .…”

Trabecular bone recovers from mechanical unloading primarily by restoring its mechanical function rather than its morphology

“…However, limitations of FE models need to be considered. Data output can be highly dependent on loading and material assumptions [42,43], a concern that was addressed here by using a simple uni-axial compression test and a linear elastic solution that reduces the influence of material properties as only relative differences within and between groups were considered. Our FE model also did not produce important data on fracture risk that is routinely generated with invasive mechanical testing procedures such as post-yield properties.…”

Experimental perspective on fallback foods and dietary adaptations in early hominins

“…However, the role of dietary seasonality in shaping the masticatory apparatus of primates and other mammals is unclear. Indeed, there is little evidence that the highly robust jaws of the australopiths Paranthropus robustus and especially Paranthropus boisei would be required of an organism that relies only seasonally on mechanically challenging foods [13]. Here, we report the results of a long-term diet-manipulation experiment conducted using an animal model that examines adaptive plasticity [14,15] in craniomandibular development vis-à-vis temporal variation in food mechanical properties.…”