Australopithecus anamensis: A finite-element approach to studying the functional adaptations of extinct hominins. Anatomical Record, 283A, 310-318

Palaeontology Research Group, Department of Human Anatomy and Cell Biology, University of Liverpool, Liverpool L69 3GE, UK.
The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology (Impact Factor: 1.54). 04/2005; 283(2):310-8. DOI: 10.1002/ar.a.20175
Source: PubMed


Australopithecus anamensis is the stem species of all later hominins and exhibits the suite of characters traditionally associated with hominins, i.e., bipedal locomotion when on the ground, canine reduction, and thick-enameled teeth. The functional consequences of its thick enamel are, however, unclear. Without appropriate structural reinforcement, these thick-enameled teeth may be prone to failure. This article investigates the mechanical behavior of A. anamensis enamel and represents the first in a series that will attempt to determine the functional adaptations of hominin teeth. First, the microstructural arrangement of enamel prisms in A. anamensis teeth was reconstructed using recently developed software and was compared with that of extant hominoids. Second, a finite-element model of a block of enamel containing one cycle of prism deviation was reconstructed for Homo, Pan, Gorilla, and A. anamensis and the behavior of these tissues under compressive stress was determined. Despite similarities in enamel microstructure between A. anamensis and the African great apes, the structural arrangement of prismatic enamel in A. anamensis appears to be more effective in load dissipation under these compressive loads. The findings may imply that this hominin species was well adapted to puncture crushing and are in some respects contrary to expectations based on macromorphology of teeth. Taking together, information obtained from both finite-element analyses and dental macroanatomy leads us to suggest that A. anamensis was probably adapted for habitually consuming a hard-tough diet. However, additional tests are needed to understand the functional adaptations of A. anamensis teeth fully.

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Available from: Gabriele A. Macho, Feb 01, 2014
    • "In addition, we use a second approach, finite element analysis (FEA) to predict cranial deformation under simulated biting loads. This technique has been increasingly used to study the response of the skull to masticatory loading in terms of the stresses and/or strains developed in the skeleton, relating these to ecological (Macho et al., 2005; Strait et al., 2009), anatomo-functional (Koolstra and Tanaka, 2009; Ross et al., 2011), evolutionary (Gröning et al., 2011; Wroe et al., 2010) and developmental factors (Kupczik et al., 2009). FEA is used in the present study to characterise the deformations of the cranium that arise in response to biting in two individuals representing the extremes of cranial variation in our available sample. "
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    ABSTRACT: The human skull is gracile when compared to many Middle Pleistocene hominins. It has been argued that it is less able to generate and withstand high masticatory forces, and that the morphology of the lower portion of the modern human face correlates most strongly with dietary characteristics. This study uses geometric morphometrics and finite element analysis (FEA) to assess the relationship between skull morphology, muscle force and cranial deformations arising from biting, which is relevant in understanding how skull morphology relates to mastication. The three-dimensional skull anatomies of 20 individuals were reconstructed from medical computed tomograms. Maximal contractile muscle forces were estimated from muscular anatomical cross-sectional areas (CSAs). Fifty-nine landmarks were used to represent skull morphology. A partial least squares analysis was performed to assess the association between skull shape and muscle force, and FEA was used to compare the deformation (strains) generated during incisor and molar bites in two individuals representing extremes of morphological variation in the sample. The results showed that only the proportion of total muscle CSA accounted for by the temporalis appears associated with skull morphology, albeit weekly. However, individuals with a large temporalis tend to possess a relatively wider face, a narrower, more vertically oriented maxilla and a lower positioning of the coronoid process. The FEAs showed that, despite differences in morphology, biting results in similar modes of deformation for both crania, but with localised lower magnitudes of strains arising in the individual with the narrowest, most vertically oriented maxilla. Our results suggest that the morphology of the maxilla modulates the transmission of forces generated during mastication to the rest of the cranium by deforming less in individuals with the ability to generate proportionately larger temporalis muscle forces.
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    • "confidencewithwhichfunctioncanbeinferredfrommorphology. Traitswhichareadvantageousandenhancethefitnessofthespeciesmayinfacthaveevolvedfor adifferentpurposeortheycouldinitiallyhavebeentheresultofrandomgeneticdrift,pleiotropy, orcorrelationwithotherstructures(GouldandLewontin1979;GouldandVrba1982).Until Fig.3Systematicdifferencesinisotropy,trabecularthickness,anddensitybetweenweight-bearing(navicular)and nonweight-bearing(capitate)bonesinmodernhumans(AdaptedfromMachoetal.2005).Ccapitate,Nnavicular; asterisksindicatesignificancelevelsusingpairedt-tests "
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    ABSTRACT: Anthropologists analyzing morphology for phylogenetic, functional, or behavioral purposes are confronted by a plethora of obstacles. Morphology is not free to vary but is subject to a number of constraints, which may be historical, developmental, and/or functional, while equivalency in function can be achieved by different means. This, together with the fact that the fossil record is scant, confounds meaningful interpretation of phylogenetic pathways and the reconstruction of function and behavior from fossilized remains. To overcome these difficulties, paleoanthropology is becoming increasingly inter- and multidisciplinary, whereby researchers draw on, and incorporate, approaches and findings obtained in other, sometimes very diverse, disciplines. This contribution briefly reviews the constraints acting on morphology, the limitations faced when interpreting form/function and behavior from morphology, and the different approaches currently explored in paleoanthropology to obtain a better understanding of hominin paleobiology. While offering exciting new possibilities, researchers should however be mindful of the limitations inherent in new technologies.
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    • "In the field of evolutionary morphology , geometric morphometric methods (GM) have transformed the ways in which evolutionary biologists study form (Kendall, 1977; Bookstein, 1991; Slice, 2005; Weber and Bookstein, 2011; Adams et al., 2013). In functional anatomy, finite element analysis (FEA) has become increasingly important for testing hypotheses in human and non-human primate evolutionary biomechanics (Macho et al., 2005; Marinescu et al., 2005; Strait et al., 2005, 2007, 2008, 2009, 2013; Kupczik et al., 2007, 2009; Wroe et al., 2007; Wang et al., 2008, 2010a,b, 2012; Gr€ oning et al., 2009; Berthaume, 2010; Panagiotopoulou, 2010, 2011a; Benazzi et al., 2011a; 2012; 2013a,b,c; Chalk et al., 2011; Dumont et al., 2011a,b; Nakashige et al., 2011; O'Higgins et al., 2011; Ross et al., 2011; Wood et al., 2011) and vertebrate biology in general (Guillet et al., 1985; Rayfield et al., 2001; Rayfield, 2004, 2005, 2011; Dumont et al., 2005, 2009; Metzger et al., 2005; Witzel, 2004; McHenry et al., 2006, 2007; Fagan et al., 2007; Bourke et al., 2008; Farke, 2008; Moreno et al., 2008; Pierce et al., 2008, 2009; Snively and Cox, 2008; Wroe et al., 2008; Arbour, 2009; Bell et al., 2009; Jasinoski et al., 2009, 2010; Manning et al., 2009; Moazen et al., 2009; Slater et al., 2009; Stayton, 2009; Fletcher et al., 2010; Panagiotopoulou, 2011b). The intersection of these two fields and the continuing integration of these two methods promises to provide a powerful toolkit with which researchers can study the mechanics and evolution of anatomical systems. "
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    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 on their magnitudes. Anat Rec, 298:122–144, 2015. © 2014 Wiley Periodicals, Inc.
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