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Session Schedule & Abstracts




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Thursday 30th June, 2016

MFS3
Symposium: Determinants of the mammalian feeding system design 3

Room: Salon B   2:30 pm–4:00 pm

Moderator(s): O. Panagiotopoulou & J. Iriarte-Diaz
MFS3-1  2:30 pm  Functional and evolutionary relationships between jaw-muscle fiber architecture and behavior: a disturbance in the force. Taylor AB*, Duke University School of Medicine; Vinyard CJ, Northeast Ohio Medical University   andrea.b.taylor@gmail.com
Abstract: Maximum bite force has long been recognized as a key performance variable related to biting and chewing and is believed to have played a critical role in the evolution of mammalian craniodental morphology. In the absence of fossilized soft tissues, paleobiological interpretations of craniofacial muscles have been forced to rely on the assumption that muscle size is a reliable proxy for muscle force and hence the key functional property of the jaw muscles. Whole muscle function is primarily influenced by two architectural properties: physiologic cross-sectional area (PCSA), which is proportional to a muscle's maximum force-generating capacity, and fiber length (Lf), which is proportional to maximum muscle excursion/stretch. Here we highlight functional and evolutionary trends in the architectural features of anthropoid primate jaw muscles. We show that while some hard-object feeders, such as tufted capuchins, have jaw-muscle architectures that improve muscle and bite forces for feeding on mechanically resistant foods, others, such as sooty mangabeys, do not. Additionally, some species have architectural features that favor jaw-muscle stretch to improve access to foods, while others have evolved architectural features that favor jaw-muscle stretching to facilitate gape and canine display to potentially improve access to mates. Some primates experience trade-offs between maximizing muscle force and muscle stretch, but others circumvent this trade-off in ways that are potentially metabolically expensive. Collectively, these findings suggest there are multiple selection pressures placed on feeding-system morphology and a variety of ways species meet competing functional demands. The multiple potential morphological solutions emphasize the importance of incorporating muscle morphology in studies linking behavioral ecology and functional morphology of the feeding system. Supported by the National Science Foundation (BCS 0452160, BCS 0962677).

MFS3-2  3:00 pm  The effect of variation of the jaw adductor musculature and cranial morphology on the masticatory performance of primates. Iriarte-Diaz J*, University of Illinois at Chicago; Akif Y, University of Illinois at Chicago; Deshpande R, University of Illinois at Chicago; Al-Hamawi O, University of Illinois at Chicago   jiriarte@uic.edu
Abstract: Substantial variation in the structural relationships within the masticatory system (i.e., among teeth, joints, and muscles) through the evolutionary history of mammals has greatly influenced the mechanical performance of the system. These changes are typically viewed as evolutionary responses associated to specific pressures; such as the need to generate occlusal force, the need to resist masticatory stresses, or the need for delicate motor control. Thus, changes in the musculo-skeletal configuration are expected to reflect adaptations to these competing and varying demands. To evaluate the relative importance of these elements in shaping the evolution of the masticatory system necessitates adequate understanding of how variation in each factor affects the mechanical performance of the system as a whole. In this study, we created a 3D mechanical model of the masticatory system to evaluate how variation in various aspects of cranio-mandibular morphology affect feeding performance. The model takes inputs from 3D models to measure the location and relative force generation of the masseter, medial pterygoid and temporalis muscles, as well as the effect of asymmetrical activation patterns, like those needed for lateral mandible displacement during feeding. We collected 3D data from a morphologically and phylogenetically diverse group of primates to evaluate the evolution of the mechanical performance of feeding. We show that the musculo-skeletal configuration of the masticatory apparatus is mechanically labile and can be varied substantially while maintaining good masticatory performance. We also evaluated clade-specific morphological changes, such as elevation of the jaw joint with respect to the occlusal plane, and their effect on the mechanical performance of the feeding system.

MFS3-3  3:30 pm  Mandibular loading, jaw-muscle activity, and symphyseal performance: elucidating the relationships among mastication, morphology, and biomechanics of the mammalian jaw. Williams SH*, Ohio University; Vinyard CJ, NEOMED; Ravosa MJ, University of Notre Dame   willias7@ohio.edu
Abstract: The morphology of the mammalian jaw is traditionally interpreted as reflecting the loading patterns it incurs during various oral behaviors such as chewing and biting. These loads are a result of jaw adductor muscle force as well as bite and temporomandibular joint reaction forces. This interpretation spans many different groups of mammals, from primates to carnivores, yet the available evidence suggesting that forces incurred during these behaviors has an evolutionary impact on jaw morphology is primarily limited to primates. Here, we relate in vivo jaw-muscle activity patterns and bone strains to patterns of jaw morphology and in vitro estimates of jaw strength in several pairwise comparisons across diverse groups of mammals including carnivores, ungulates and primates. Whereas some aspects of morphology (e.g., symphyseal fusion and a relatively large symphyseal cross-sectional area) have relatively consistent links to muscle activity patterns and strength estimates across mammals, the relationship between morphology and specific loading patterns derived from strain data is less clear. Moreover, mandibular strain patterns during mastication are varied and complex when considered relative to variation in symphyseal fusion across mammals, making links among specific in vivo loading regimes, performance and morphology more difficult to interpret across mammals. We consider the consistent features across these clade-specific relationships among activity, performance and form to help identify persistent factors driving the evolutionary changes in mammalian jaw form across mammals. Funding: National Science Foundation IOS-0520855 and DBI-1062327 to SHW, BCS-0959438 and DBI-1062332 to CJV, and BCS-0924592/1214766 to MJR and CJV.



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