Finite Element Analysis of the Cingulata Jaw: An Ecomorphological Approach to Armadillo’s Diets

Abstract

Finite element analyses (FEA) were applied to assess the lower jaw biomechanics of cingulate xenarthrans: 14 species of armadillos as well as one Pleistocene pampathere (11 extant taxa and the extinct forms Vassallia, Eutatus and Macroeuphractus). The principal goal of this work is to comparatively assess the biomechanical capabilities of the mandible based on FEA and to relate the obtained stress patterns with diet preferences and variability, in extant and extinct species through an ecomorphology approach. The results of FEA showed that omnivorous species have stronger mandibles than insectivorous species. Moreover, this latter group of species showed high variability, including some similar biomechanical features of the insectivorous Tolypeutes matacus and Chlamyphorus truncatus to those of omnivorous species, in agreement with reported diets that include items other than insects. It remains unclear the reasons behind the stronger than expected lower jaw of Dasypus kappleri. On the other hand, the very strong mandible of the fossil taxon Vassallia maxima agrees well with the proposed herbivorous diet. Moreover, Eutatus seguini yielded a stress pattern similar to Vassalia in the posterior part of the lower jaw, but resembling that of the stoutly built Macroeuphractus outesi in the anterior part. The results highlight the need for more detailed studies on the natural history of extant armadillos. FEA proved a powerful tool for biomechanical studies in a comparative framework.

Accounting for differences in element size and homogeneity when comparing Finite Element models: Armadillos as a case study

“…This material is housed in different museums (Table 1). Although we previously developed an FEA on these species (Serrano-Fochs et al, 2015), this time we add six new specimens in an effort to examine intraspecific variability. FEA models.…”

“…Two main muscles (temporalis and masseter) were included in the model as force vector between the centroid of the muscular attachment in the lower mandible and the centroid of the equivalent muscle attachment in the skull (Serrano-Fochs et al, 2015). Following this direction, the force vector was applied in the insertion area of each muscle and because the amount of force that a muscle produces depends on the section of the muscle (Alexander, 1992), the force was applied to all the models in both muscles insertion areas (masseter and temporalis) and depending of the proportion of its insertion area described in Table 1.…”

“…The boundary conditions were defined and placed representing the loads, displacements and constraining anchors that the structure experiences during function as in previous works (Serrano-Fochs et al, 2015). They simulate the mandible constrained at the most anterior part and a constraint on the condyle at the level of the mandibular notch representing the immobilization of the mandible.…”

“…In the absence of data for Cingulata or any close relative, or any mammal clade with similar bone structure, the mandible properties of Macaca mulatta was used: E (Elasticity Modulus) = 21,000 MPa and v (Poisson coefficient) = 0.45 (Dechow and Hylander, 2000). The choice of this taxon it is due to its ecological history and is discussed in Serrano-Fochs et al (2015), although in a comparative analysis, these material properties are not relevant in the results of stress . The data obtained in the FEA will be the Von Mises stress distribution which, according to Doblaré et al (2004), is the most accurate variable to predict stresses when isotropic properties with a cortical bone as a material are used.…”

“…There is a certain lack of information about good quantitative descriptors to compare different computational models. Quantifying stress data at specific points has been useful in ecomorphological analyses (Fortuny et al, 2011;Serrano-Fochs et al, 2015), but these analyses are hindered by the lack of information about the whole model. Dumont et al (2005) and McHenry et al (2007) first used Von Mises Stress values as a descriptive statistic to compare the results of different FE analyses, and this method has been used frequently since then (Parr et al, 2012;Aquilina et al, 2013;Figueirido et al, 2014;Fish and Stayton, 2014;Neenan et al, 2014).…”