Biomechanical Implications of Intraspecific Shape Variation in Chimpanzee Crania: Moving Toward an Integration of Geometric Morphometrics and Finite Element Analysis

Abstract

In a broad range of evolutionary studies, an understanding of intraspecific variation is needed in order to contextualize and interpret the meaning of variation between species. However, mechanical analyses of primate crania using experimental or modeling methods typically encounter logistical constraints that force them to rely on data gathered from only one or a few individuals. This results in a lack of knowledge concerning the mechanical significance of intraspecific shape variation that limits our ability to infer the significance of interspecific differences. This study uses geometric morphometric methods (GM) and finite element analysis (FEA) to examine the biomechanical implications of shape variation in chimpanzee crania, thereby providing a comparative context in which to interpret shape-related mechanical variation between hominin species. Six finite element models (FEMs) of chimpanzee crania were constructed from CT scans following shape-space Principal Component Analysis (PCA) of a matrix of 709 Procrustes coordinates (digitized onto 21 specimens) to identify the individuals at the extremes of the first three principal components. The FEMs were assigned the material properties of bone and were loaded and constrained to simulate maximal bites on the P3 and M2. Resulting strains indicate that intraspecific cranial variation in morphology is associated with quantitatively high levels of variation in strain magnitudes, but qualitatively little variation in the distribution of strain concentrations. Thus, interspecific comparisons should include considerations of the spatial patterning of strains rather than focus only their magnitude.

The Effect of Varying Jaw‐elevator Muscle Forces on a Finite Element Model of a Human Cranium

“…Thus maximal muscle forces might be more or less accurately estimated from bony proxies (Wroe et al, ) or estimated from data corresponding to other, related species (Strait et al, ; Smith et al, ). Forces might be applied to simulate maximum (100%) activation of all muscles (Smith et al, ) or some more complex muscle activation pattern might be used (Kupczik et al, ). This study aimed to assess the sensitivity of some aspects of FE model performance to such variations in muscle activations; namely strains, bite forces, TMJ forces and global modes of model deformation.…”

Non‐Destructive Determination of Muscle Architectural Variables Through the Use of DiceCT

“…As mechanical advantage will vary throughout a single muscle, regional differences in architectural parameters such as fascicle length or pennation angle may be related to differences in moment arm length between anteriorly-and posteriorly-positioned fascicles within this muscle. Integrating data on muscle fascicle length and orientation into digital mediums of biomechanical modeling such as multibody dynamics (Curtis et al, 2008;Shi et al, 2012;Fitton et al, 2012;Gr€ oning et al, 2013;Watson et al, 2014) or finite element analysis (Kupczik et al, 2007(Kupczik et al, , 2009Chalk et al, 2011;Wang et al, 2010;Dumont et al, 2011;Ross et al, 2011;Tseng et al, 2011;Fitton et al, 2012;Smith et al, 2015) may allow us to directly address the relationship between muscle architectural variables and other functional determinants of muscle performance.…”

A Virtual geometric morphometric approach to the quantification of long bone bilateral asymmetry and cross‐sectional shape

“…This pattern raises a number of questions about the plasticity of size compared to shape, from a functional, but also developmental and evolutionary, perspective. FEA is an engineering technique that may be applied to CT scans of skeletal elements to assess the magnitude and distribution of stress under specific loading cases, and the possibility for integration with GMM data has been promoted as a valuable addition to virtual form-function studies (e.g., Parr et al, 2012;O'Higgins and Milne, 2013;Smith et al, 2015). At present, neither of these avenues has been explored in the biomechanical study of long bones because a GMM approach, which offers a pathway to address both, has yet to be implemented.…”

“…In one application, hypothetical forms could be created by warping GMM landmark configurations (e.g., Werneburg et al, 2015), and the function of hypothetical virtual forms may be tested using finite element analysis (FEA). FEA is an engineering technique that may be applied to CT scans of skeletal elements to assess the magnitude and distribution of stress under specific loading cases, and the possibility for integration with GMM data has been promoted as a valuable addition to virtual form-function studies (e.g., Parr et al, 2012;O'Higgins and Milne, 2013;Smith et al, 2015).…”