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Session Schedule & Abstracts

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Thursday 30th June, 2016

Symposium: Determinants of the mammalian feeding system design 2

Room: Salon B   11:30 am–1:00 pm

Moderator(s): O. Panagiotopoulou & J. Iriarte-Diaz
MFS2-1  11:30 am  Variations in the material properties of mammalian and non-human primate jaws. Dechow PC*, Texas A&M University Baylor College of Dentistry
Abstract: Cortical bone material properties including density and elastic properties (elastic and shear moduli, and Poisson's ratios) are essential for understanding the complex biomechanics of individual bones to muscle forces and extrinsic loadings. In particular, variations in cortical bone anisotropies are significant in determining the relationship between stress and strain in bone. In primate and human evolution, research on the craniofacial skeleton, including the mandible, suggest that variations in such properties may represent evolutionary adaptations to unique craniofacial functions or patterns of development. My laboratory has conducted comparative studies on the material properties of macaques, baboons, chimpanzees, gorillas, capuchins, alligators, bats, pigs, and humans. Methodology included measurements of bone density using Archimedes principle, and ultrasonic techniques modified to calculate 3D material properties of cortical bone. Such data are required to improve the accuracy of finite element models. Here comparisons are made across species to assess commonalities and differences in mandibular material structure. Overall, these results reveal complex patterns of skeletal maturation, much of which can be attributed to increasing bone density with age, especially regarding elastic and shear moduli. Other variables such as anisotropy and orientation of maximum stiffness are less related to bone density and differences suggest variations in internal microstructure with adaptation and growth. Interpretation of the impact of these differences between regions on the relationship between stress and strain patterns requires an understanding of the different loading and boundary conditions at each region during function. For this reason, it is doubtful whether one can generalize from region to region and across species on the impact of including material properties in a functional analysis. Support: NSF Physical Anthropology HOMINID program NSF-BCS-0725141.

MFS2-2  12:00 pm  Impact of feeding behavior on the deformations of the macaque mandible. Panagiotopoulou O*, School of Biomedical Sciences, The University of Queensland, Australia and Department of Biomedical Sciences, The Royal Veterinary College, UK; Iriarte-Diaz J, Department of Oral Biology, University of Illinois Chicago, USA; Wilshin S, Department of Biomedical Sciences, The Royal Veterinary College, UK; Dechow PC, Department of Biomedical Sciences, Texas A&M University Baylor College of Dentistry, USA; Taylor AB, Department of Orthopaedic Surgery, Duke University School of Medicine, USA and Department of Evolutionary Anthropology, Duke University, USA; Grosse I, Department of Mechanical and Industrial Engineering, University of Massachusetts, USA; Ross CF, Department of Organismal Biology and Anatomy, University of Chicago, USA
Abstract: Developmental studies reveal links between mandibular corpus morphology and diet. However, comparative research in primates does not strongly support links between food mechanical properties (FMPs) and mandibular corpus morphology. We investigated the effects of FMPs with variable stiffness (E, range=0.5-34MPa) and toughness (R, range=105-965Jm-2) on mandibular strain patterns and magnitudes using in vivo experiments and finite element models (FEMs). We hypothesized that variation in strain magnitudes and orientations when chewing items with different FMPs is minimal at the corpus and maximal at the lingual symphysis, since the latter is subjected to high strains during mastication. We further hypothesized that principal strain in the mandibular corpora is more strongly affected by variations in bite locations than is the symphysis. Results confirm that across all food items mean in vivo maximum principal strain (ε1) in the corpus had a range of 13-227 µε for nuts; 15-291 µε for dry fruit and 9-149 µε for soft food and comparative results were obtained from the FEMs. Nevertheless, the mean ε1 in the symphysis in FEMs had a range of 19-1682 µε for nuts, 3-1773 µε for dry fruit, and 7-768 µε for soft food, evidently higher than the corpus. Results also confirmed that ε1 at the lingual symphysis is relatively insensitive to variation in bite location, whilst variations in magnitudes and patterns were encountered in the chewing side corpus. These data suggest that if variation in primate mandibular morphology is driven by variation in strain patterns and magnitudes, then it is likely related to a combination of both feeding behavior and FMPs, but with different factors being important at different mandibular sites. Funding: Marie Curie European Re-integration Grant ERG-MACACA 267207 to OP. SBMS, UQ start up Project Grant 606441 to OP. BBSRC Grant BB/J021504/1 to SW. NSF BCS 0962677 Grant to ABT.

MFS2-3  12:30 pm  What's gape got to do with it? Examining osteological correlates of jaw gape in primates. Terhune CE*, University of Arkansas
Abstract: Considerable attention has been given to bite force as a performance variable in vertebrate and mammalian feeding, yet until recently less interest has been given to the adaptive significance of variation in jaw gape. The publication of in vivo primate gapes by Hylander provides an opportunity to examine potential correlates between gape and osteology, which can help to elucidate the morphological patterns employed by primates to achieve large gapes, whether for dietary or social behaviors. The present study examines osteological features of the mandible, temporomandibular joint, and masticatory muscles in a sample of 21 catarrhine primates. The relationship between gape, canine projection, and body mass were examined, and osteological measurements were regressed on gape separately for females and males. A significant but weak relationship was identified between body mass and gape and, as in previous work, canine projection was significantly correlated with gape. Nearly all osteological features examined scaled with negative allometry and were significantly correlated with gape in both sexes; males showed especially strong relationships between gape and mandible length and measures of TMJ length and curvature. Similarly, geometric morphometric analyses found a strong relationship between overall craniofacial shape and gape. However, t-tests for relative differences between sexes within each species revealed that patterns of osteological differences varied considerably across taxa. Together, these data suggest that, though there are general patterns across catarrhine primates in how craniofacial morphology is linked to gape, species with considerable sexual dimorphism in gape achieve these differences in multiple ways. These differences in the osteological correlates of gape within species may be informative for understanding the trade-offs between gape vs. bite force production.

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