School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin, China.
Johannes Gutenberg University Mainz, Institute of Geosciences, Mainz, Germany.
PLoS One. 2019 Apr 17;14(4):e0214510. doi: 10.1371/journal.pone.0214510. eCollection 2019.
There is considerable debate regarding whether mandibular morphology in ungulates primarily reflects phylogenetic affinities or adaptation to specific diet. In an effort to help resolve this debate, we use three-dimensional finite element analysis (FEA) to assess the biomechanical performance of mandibles in eleven ungulate taxa with well-established but distinct dietary preferences. We found notable differences in the magnitude and the distribution of von Mises stress between Artiodactyla and Perissodactyla, with the latter displaying lower overall stress values. Additionally, within the order Artiodactyla the suborders Ruminantia and Tylopoda showed further distinctive stress patterns. Our data suggest that a strong phylogenetic signal can be detected in biomechanical performance of the ungulate mandible. In general, Perissodactyla have stiffer mandibles than Artiodactyla. This difference is more evident between Perissodactyla and ruminant species. Perissodactyla likely rely more heavily on thoroughly chewing their food upon initial ingestion, which demands higher bite forces and greater stress resistance, while ruminants shift comminution to a later state (rumination) where less mechanical effort is required by the jaw to obtain sufficient disintegration. We therefore suggest that ruminants can afford to chew sloppily regardless of ingesta, while hindgut fermenters cannot. Additionally, our data support a secondary degree of adaptation towards specific diet. We find that mandibular morphologies reflect the masticatory demands of specific ingesta within the orders Artiodactyla and Perissodactyla. Of particular note, stress patterns in the white rhinoceros (C. simum) look more like those of a general grazer than like other rhinoceros' taxa. Similarly, the camelids (Tylopoda) appear to occupy an intermediate position in the stress patterns, which reflects the more ancestral ruminating system of the Tylopoda.
关于有蹄类动物的下颌形态主要反映系统发育关系还是适应特定饮食，存在相当大的争议。为了帮助解决这一争议，我们使用三维有限元分析（FEA）来评估 11 种具有明确但不同饮食偏好的有蹄类动物的下颌骨的生物力学性能。我们发现偶蹄目和奇蹄目之间在 von Mises 应力的大小和分布上存在显著差异，后者的整体应力值较低。此外，在偶蹄目内部，反刍亚目和奇蹄目显示出进一步独特的应力模式。我们的数据表明，在有蹄类动物下颌骨的生物力学性能中可以检测到强烈的系统发育信号。一般来说，奇蹄目动物的下颌骨比偶蹄目动物更硬。这种差异在奇蹄目动物和反刍动物之间更为明显。奇蹄目动物可能更依赖于在最初摄入时彻底咀嚼食物，这需要更高的咬合力和更高的抗应力能力，而反刍动物则将粉碎过程转移到后期（反刍），此时下颌需要更少的机械力即可获得足够的分解。因此，我们认为反刍动物可以随意咀嚼，而不管食物如何，而后肠发酵动物则不能。此外，我们的数据支持对特定饮食的二级适应。我们发现，下颌形态反映了特定有蹄目和奇蹄目动物的饮食需求。值得注意的是，白犀牛（Ceratotherium simum）的应力模式看起来更像是一般食草动物，而不是其他犀牛类群。同样，骆驼类（奇蹄目）在应力模式中似乎占据了中间位置，这反映了奇蹄目更原始的反刍系统。
