Allometry of masticatory loading parameters in mammals.

Considerable research on the scaling of loading patterns in mammalian locomotor systems has not been accompanied by a similarly comprehensive analysis of the interspecific scaling of loading regimes in the mammalian masticatory complex. To address this deficiency, we analyzed mandibular corpus bone strain in 11 mammalian taxa varying in body size by over 2.5 orders of magnitude, including goats, horses, alpacas, pigs, and seven primate taxa. During alert chewing and biting of hard/tough foods, bone-strain data were collected with rosette gauges placed along the lateral aspect of the mandibular corpus below the molars or premolars. Bone-strain data were used to characterize relevant masticatory loading parameters: peak loading magnitudes, chewing cycle duration, chewing frequency, occlusal duty factor, loading rate, and loading time. Interspecific analyses indicate that much as observed in limb elements, corpus peak-strain magnitudes are similar across mammals of disparate body sizes. Chewing frequency is inversely correlated with body size, much as with locomotor stride frequency. Some of this allometric variation in chewing frequency appears to be due to a negative correlation with loading time, which increases with body size. Similar to the locomotor apparatus, occlusal duty factor, or the duration of the chewing cycle during which the corpus is loaded, does not vary with body size. Peak principal-strain magnitudes are most strongly positively correlated with loading rate and only secondarily with loading, with this complex relationship best described by a multiple regression equation with an interaction term between loading rate and loading time. In addition to informing interpretations of craniomandibular growth, form, function, and allometry, these comparisons provide a skeleton-wide perspective on the patterning of osteogenic stimuli across body sizes.