The highly derived facial morphologyMorphology of the genus Paranthropus is sensibly linked to feeding behavior. While there have been detailed assessments of biomechanical performance in Paranthropus, there is justified skepticism over whether the particulars of diet are recoverable from consideration of morphologyMorphology alone. At issue are conflicting interpretations over microwearMicrowear and isotopic data, in addition to the question of what aspects of the masticatory stress environmentEnvironment are tangibly associated with osseous facial anatomy. The mechanobiological perspective proceeds from the premise the stress environmentEnvironment shapes skeletal morphologyMorphology in predictable, but not necessarily optimal ways. The rich experimental foundation of this research suggests that a number of distinct load histories could induce facial hypertrophy, including, but not limited to, one induced by hard-object feeding. MasticationMastication of a tough diet, which involves more masticatory cycles per day but with reduced peak stresses compared to durophagyDurophagy, is also plausible from a mechanobiological perspective. Consideration of the fossil mandibular evidence suggests that the most important aspect of masticatory stress in Paranthropus was shearShear, under which bone has relatively low strength and reduced fatigueFatigue life. Published reconstructions of masticatory forces in OH 5OH 5 suggest that peak shear stressesShear stress may have been relatively low in Paranthropus. This yields a needlessly high nominal safety factorSafety factor in these australopith mandibles. The possibility that Paranthropus mandibles were adapted to resist fatigueFatigue failure is explored.