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Abstract The evolution of complex dentitions in mammals was a major innovation that facilitated the expansion into new dietary niches, which imposed selection for tight form–function relationships. Teeth allow mammals to ingest and process food items by applying forces produced by a third-class lever system composed by the jaw adductors, the cranium, and the mandible. Physical laws determine changes in jaw adductor (biting) forces at different bite point locations along the mandible (outlever), thus, individual teeth are expected to experience different mechanical regimes during feeding. If the mammal dentition exhibits functional adaptations to mandible feeding biomechanics, then teeth are expected to have evolved to develop mechanically advantageous sizes, shapes, and positions. Here, we present bats as a model system to test this hypothesis and, more generally, for integrative studies of mammal dental diversity. We combine a field-collected dataset of bite forces along the tooth row with data on dental and mandible morphology across 30 bat species. We (1) describe, for the first time, bite force trends along the tooth row of bats; (2) use phylogenetic comparative methods to investigate relationships among bite force patterns, tooth, and mandible morphology; and (3) hypothesize how these biting mechanics patterns may relate to the developmental processes controlling tooth formation. We find that bite force variation along the tooth row is consistent with predictions from lever mechanics models, with most species having the greatest bite force at the first lower molar. The cross-sectional shape of the mandible body is strongly associated with the position of maximum bite force along the tooth row, likely reflecting mandibular adaptations to varying stress patterns among species. Further, dental dietary adaptations seem to be related to bite force variation along molariform teeth, with insectivorous species exhibiting greater bite force more anteriorly, narrower teeth and mandibles, and frugivores/omnivores showing greater bite force more posteriorly, wider teeth and mandibles. As these craniodental traits are linked through development, dietary specialization appears to have shaped intrinsic mechanisms controlling traits relevant to feeding performance.
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This content will become publicly available on August 20, 2026
Multiscale functional specialization of rodent jaw systems; correlated bite force adaptations at molecular, muscular, and skeletal scales
Abstract Bite force is a key metric of organismal performance, and expression of masticatory myosin (MHC-M) is associated with high bite force. However, skeletal muscles are multiscale structures, and it remains unclear how adaptations for force production are integrated across scales. We analyzed myosin isoform composition and physiological cross-sectional area of the jaw muscles and measured their dynamic moment armsex vivousing XROMM (X-ray Reconstruction Of Moving Morphology) in six rodent species. We found modifications at all scales in hard biters (grey squirrels) to prioritize force production. Related species (chipmunk, woodchuck and red squirrel) showed a mix of adaptations across scales, with different muscle phenotypes producing equivalent bite force outputs. By contrast, rat and guinea pig showed modifications at all scales consistent with reduced force production. Our results suggest that selection for ecologically relevant traits – including MHC-M expression – occurs at multiple organizational scales within the rodent craniofacial system.
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- Award ID(s):
- 2217246
- PAR ID:
- 10632490
- Publisher / Repository:
- Research Square
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Research Square
- Sponsoring Org:
- National Science Foundation
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