Masticatory biomechanics in the rabbit : a multi-body dynamics analysis

Acknowledgement We thank Sue Taft (University of Hull) for the µCT-scanning of the rabbit specimen used in this study. We also thank Raphaël Cornette, Jacques Bonnin, Laurent Dufresne, and l'Amicale des Chasseurs Trappistes (ACT) for providing permission and helping us capture the rabbits used for the in vivo bite force measurements at la Réserve Naturelle Nationale de St Quentin en Yvelines, France.Peer reviewedPublisher PD

The Form-Function Complex of the Primate Masticatory Apparatus

Craniofacial morphology varies considerably between primate species with many aspects of structural variation occurring within the masticatory apparatus. These variations in masticatory fonn are frequently attributed to differences in diet however elucidating the relationship between masticatory form and function is complex. This study combines the techniques of shape analysis in a comparative study of the primate masticatory apparatus with three-dimensional biomechanical modelling of primate jaw mechanics. The relationship between masticatory form and function is investigated within a subfamily ofprimates, the Cercopithecinae. Species within this group display a range of masticatory forms, inhabit a wide range of environments, have varying diets and share close phylogenetic relationships making them an ideal group to investigate the relationship between structure and function. Using the techniques of geometric morphometrics a shape analysis was conducted in which variations within the masticatory forms of the Cercopithecinae were quantified. Functional predictions of observed shape differences were made and considered in light of known environmental and ecological factors with particular emphasis on dietary specialisations and fall back foods. The results of the shape analysis indicate that differences in body size, strata utilisation, and diet appear to play a major role in structuring adult morphological diversity within and among the Cercopithecinae. Many of the shape differences associated with an increased body size appear to reflect the selective pressures of increased predation risk, including increases in the length ofthe jaw and canine teeth. These morphological traits are associated with the production of a large gape and are hypothesised to be functional adaptations to the use of canines as weapons. Other major shape differences apparent between the Cercopithecinae were those associated with the proportion of leaves and fruit in the diet. The highly frugivorous Mandril/us species possessed features associated with increasing gape and retractile motions of the mandible ideal for incision of large fruits. By contrast the dietary specialist Theropithecus gelada possessed features associated with increasing the efficiency of food breakdown and muscle force production, necessary to process their more abrasive foodstuff (i.e. grasses)

The Mechanical Significance of the Temporal Fasciae in Macaca fascicularis: An Investigation Using Finite Element Analysis

Computational finite element analyses (FEAs) of the skull predict structural deformations under user specified loads and constraints, with results normally presented as stress and strain distributions over the skull's surface. The applied loads are generally a representation of the major adductor musculature, with the skull constrained at bite positions and at the articulating joints. However, virtually all analyses ignore potentially important anatomical structures, such as the fasciae that cover the temporalis muscle and attach onto the zygomatic arch. In vivo experimental studies have shown that removal of the temporal fasciae attachment onto the zygomatic arch in Cebus monkeys results in significant bone adaptation and remodeling in this region, suggesting the fasciae play an important role in stabilising the arch during biting. Here we investigate this potential stabilising role by carrying out FEAs of a macaque skull with and without temporal fasciae included. We explore the extent to which the zygomatic arch might be stabilized during biting by a synchronized tensioning of the temporal fasciae, acting to oppose masseteric contraction forces. According to our models, during temporalis muscle bulging the forces generated within the tensioned temporal fasciae are large enough to oppose the pull of the masseter. Further, a near bending-free state of equilibrium within the arch can be reached, even under forceful biting. We show that it is possible to eliminate the high strain gradients in and around the zygomatic arch that are present in past computational studies, with strains being more uniform in magnitude than previously thought. © 2011 Wiley-Liss, Inc

Finite element analysis of the cranium : Validity, sensitivity and future directions

Finite element analysis (FEA) is increasingly applied in skeletal biomechanical research in general, and in fossil studies in particular. Underlying such studies is the principle that FEA provides results that approximate reality. This paper provides further understanding of the reliability of FEA by presenting a validation study in which the deformations experienced by a real cadaveric human cranium are compared to those of an FE model of that cranium under equivalent simulated loading. Furthermore, model sensitivity to simplifications in segmentation and material properties is also assessed. Our results show that absolute deformations are not accurately predicted, but the distribution of the regions of relatively high and low strains, and so the modes of global deformation, are reasonably approximated

Geometric morphometrics and finite elements analysis : Assessing the functional implications of differences in craniofacial form in the hominin fossil record

The study of morphological variation in the hominin fossil record has been transformed in recent years by the advent of high resolution 3D imaging combined with improved geometric morphometric (GM) toolkits. In parallel, increasing numbers of studies have applied finite elements analysis (FEA) to the study of skeletal mechanics in fossil and extant hominoid material. While FEA studies of fossils are becoming ever more popular they are constrained by the difficulties of reconstruction and by the uncertainty that inevitably attaches to the estimation of forces and material properties. Adding to these modelling difficulties it is still unclear how FEA analyses should best deal with species variation.Comparative studies of skeletal form and function can be further advanced by applying tools from the GM toolkit to the inputs and outputs of FEA studies. First they facilitate virtual reconstruction of damaged material and can be used to rapidly create 3D models of skeletal structures. Second, GM methods allow variation to be accounted for in FEA by warping models to represent mean and extreme forms of interest. Third, GM methods can be applied to compare FEA outputs - the ways in which skeletal elements deform when loaded. Model comparisons are hampered by differences in material properties, forces and size among models but how deformations from FEA are impacted by these parameters is increasingly well understood, allowing them to be taken into account in comparing FEA outputs.In this paper we review recent advances in the application of GM in relation to FEA studies of craniofacial form in hominins, providing examples from our recent work and a critical appraisal of the state of the art

Metrics of biomass, live-weight gain and nitrogen loss of ryegrass sheep pasture in the 21st century

This study was partially supported by Soil to Nutrition, Rothamsted Research’s Institute Strategic Programme supported by the Biotechnology and Biological Sciences Research Council (BBS/E/C/000I0320).The North Wyke Farm Platform is a UK National Capability, also supported by the Biotechnology and Biological Sciences Research Council (BBS/E/C/000J0100).This study was also partially supported by the Natural Environment Research Council’s ADVENT project (NERC NE/M019691/1).Climate data were measured at the MIDAS Land Surface Station DLY3208 DEVON, UK, a weather station of the UK Meteorological Office. We would especially like to thank Dr Nadine Loick of Rothamsted Research for advice on preparation of N2O model calibration parameters, and the data team of the North Wyke Farm Platform. We owe our gratitude to the late Mr Robert Orr, grassland specialist at the North Wykesite, for his invaluable advice and information on sward growth.Peer reviewedPublisher PD

Comparison of cranial performance between mainland and two island subspecies of the Arctic fox Vulpes lagopus (Carnivora: Canidae) during simulated biting

Island subspecies of the Arctic fox Vulpes lagopus differ morphologically from the mainland subspecies. In particular, differences in cranial form may reflect varied biomechanical adaptations associated with hunting and feeding behaviours. We tested the hypothesis that the observed cranial differences between two island foxes (living on two North Pacific islands) and those living on the mainland have no impact on biomechanical performance during simulated biting. 3D cranial models of three Arctic fox subspecies were compared based on biomechanical parameters (e.g. local strain and large-scale deformation). Finite elements (FE) analyses were used to simulate equivalent biting loads, and geometric morphometrics was used to compare the modes of deformation among the models. The results showed differences in local strains and modes of global deformation among the three subspecies; the mainland subspecies was particularly distinct from the island subspecies. The representative cranium of the mainland subspecies experienced higher strain than that of both island subspecies during all bites. However, the findings highlight issues that arise when relating biomechanical performance, measured via FE analyses, to the foods consumed rather than to the mechanical properties of the individual’s diet. Additional physical properties data for each prey type are necessary to determine the extent to which the present findings reflect biomechanical adaptations to diet and prey acquisition