A Preliminary Analysis of Correlations between Chewing Motor Patterns and Mandibular Morphology across Mammals

What does feeding system morphology tell us about feeding?

“…These results support Hiiemae and Kay's hypothesis that: “changes in the morphology of the masticatory apparatus in general, and of the cheek teeth in particular, have not involved any significant change in the pattern of mastication as expressed by absolute cycle times or the percentage duration of each of the strokes” . Whether this reflects conservation of an inherited central motor pattern across generations and lineages and/or geometric constraints imposed by the functional requirements of mastication remains to be determined …”

“…Another reason for the lack of strong relationships between craniomandibular morphology and either feeding behavior or diet may be the influence of phylogenetic history on primate feeding system design. When analyses have been done in a phylogenetic context, they have revealed important patterns: very weak scaling of daily feeding time with body size; no relationship between gut mean retention time and body size; no relationship between working or balancing jaw elevator EMG amplitude ratios and jaw robusticity; and no relationship between superficial masseter W/B ratios and mandibular corpus area; but a relationship between balancing‐side deep masseter timing and symphyseal cross‐sectional area . Many of the biomechanical studies of the last few decades have not used phylogenetic techniques.…”

“…The distribution of variance in feeding system morphology and behavior across primate phylogeny needs to be better documented. As more data on jaw kinematics and jaw muscle EMG patterns accumulate, it will be interesting to see whether the conserved primate jaw kinematic patterns reflect conservation of an inherited central motor pattern and/or geometric constraints imposed by the functional requirements of mastication …”

“…Recent support for this hypothesis comes from the observation that adult Propithecus verreauxi , which have convergently evolved a nearly completely fused mandibular symphysis, also resemble anthropoids in displaying relatively high EMG amplitudes in the balancing‐side deep masseter and posterior temporalis, which also peak late in the power stroke . Thus, differences between anthropoids and most strepsirrhines in how jaw movements are produced and how working and balancing muscles are recruited have consequences for mandibular design . Indeed, balancing‐side deep masseter amplitudes and timing appear to be linked to symphyseal morphology across other mammals that display transverse movements of the mandible during the power stroke of mastication …”

“…Thus, differences between anthropoids and most strepsirrhines in how jaw movements are produced and how working and balancing muscles are recruited have consequences for mandibular design . Indeed, balancing‐side deep masseter amplitudes and timing appear to be linked to symphyseal morphology across other mammals that display transverse movements of the mandible during the power stroke of mastication …”