Ross Callum F, Iriarte-Diaz Jose, Platts Ellen, Walsh Treva, Heins Liam, Gerstner Geoffrey E, Taylor Andrea B
Department of Organismal Biology and Anatomy, The University of Chicago, USA.
Department of Oral Biology, College of Dentistry, University of Illinois at Chicago, USA.
J Hum Evol. 2017 May;106:119-132. doi: 10.1016/j.jhevol.2017.02.007. Epub 2017 Mar 31.
The relative importance of pendulum mechanics and muscle mechanics in chewing dynamics has implications for understanding the optimality criteria driving the evolution of primate feeding systems. The Spring Model (Ross et al., 2009b), which modeled the primate chewing system as a forced mass-spring system, predicted that chew cycle time would increase faster than was actually observed. We hypothesized that if mandibular momentum plays an important role in chewing dynamics, more accurate estimates of the rotational inertia of the mandible would improve the accuracy with which the Spring Model predicts the scaling of primate chew cycle period. However, if mass-related momentum effects are of negligible importance in the scaling of primate chew cycle period, this hypothesis would be falsified. We also predicted that greater "robusticity" of anthropoid mandibles compared with prosimians would be associated with higher moments of inertia. From computed tomography scans, we estimated the scaling of the moment of inertia (I) of the mandibles of thirty-one species of primates, including 22 anthropoid and nine prosimian species, separating I into the moment about a transverse axis through the center of mass (I) and the moment of the center of mass about plausible axes of rotation. We found that across primates I increases with positive allometry relative to jaw length, primarily due to positive allometry of jaw mass and I, and that anthropoid mandibles have greater rotational inertia compared with prosimian mandibles of similar length. Positive allometry of I of primate mandibles actually lowers the predictive ability of the Spring Model, suggesting that scaling of primate chew cycle period, and chewing dynamics in general, are more strongly influenced by factors other than scaling of inertial properties of the mandible, such as the dynamic properties of the jaw muscles and neural control. Differences in cycle period scaling between chewing and locomotion systems reinforce the suggestion that displacement and force control are more important in the design of feeding systems than energetics and speed.
钟摆力学和肌肉力学在咀嚼动力学中的相对重要性，对于理解驱动灵长类动物进食系统进化的最优标准具有重要意义。弹簧模型（Ross等人，2009b）将灵长类动物的咀嚼系统模拟为一个受迫质量 - 弹簧系统，预测咀嚼周期时间的增加速度会比实际观察到的更快。我们假设，如果下颌动量在咀嚼动力学中起重要作用，那么对下颌转动惯量的更准确估计将提高弹簧模型预测灵长类动物咀嚼周期缩放的准确性。然而，如果与质量相关的动量效应在灵长类动物咀嚼周期缩放中重要性可忽略不计，那么这个假设将被证伪。我们还预测，与原猴亚目相比，类人猿下颌更大的“粗壮度”将与更高的转动惯量相关。通过计算机断层扫描，我们估计了31种灵长类动物下颌的转动惯量（I）缩放情况，包括22种类人猿和9种原猴亚目物种，将I分为通过质心的横轴方向的转动惯量（I）和质心绕合理旋转轴的转动惯量。我们发现，在所有灵长类动物中，I相对于颌骨长度呈正异速生长增加，这主要是由于颌骨质量和I的正异速生长，并且与类似长度的原猴亚目下颌相比，类人猿下颌具有更大的转动惯量。灵长类动物下颌I的正异速生长实际上降低了弹簧模型的预测能力，这表明灵长类动物咀嚼周期缩放以及一般的咀嚼动力学，受下颌惯性特性缩放之外的其他因素影响更大，如下颌肌肉的动力学特性和神经控制。咀嚼和运动系统在周期缩放方面的差异进一步表明，在进食系统设计中，位移和力控制比能量和速度更重要。
