Finite Element Analyses of the Mammalian Skull: The Impact of Biting Behavior

哺乳动物的咬人方式和进食的生物力学--伊丽莎白·R·杜蒙(PI)，伊恩·R·格罗斯(Co-PI)，马萨诸塞州阿默斯特大学哺乳动物的进化史在很大程度上是一个关于开发更广泛的食物资源的故事。虽然最早的哺乳动物是食虫动物，但现代哺乳动物专门从事从昆虫到水果、树叶、肉类和浮游生物的饮食。这种饮食的多样性反映在头骨的形状上--头骨是哺乳动物用来咬和咀嚼食物的主要工具。然而，重要的是，推动这种多样性演变的潜在机制尚不清楚。这项研究探索了咬合过程中产生的力与哺乳动物头骨的解剖之间生物力学联系的重要性，这些解剖可以安全和最佳地承受和分散这些力。此外，这项研究调查了这种关系在头骨形状多样性进化中的作用。以前对哺乳动物进食的分析采取了两种方法之一，每一种方法都有固有的局限性。广泛的比较研究证明了头骨形状和饮食之间的相关性，但没有测试这种相关性背后的因果机制。另一方面，详细的实验研究记录了骨骼和肌肉在进食过程中的行为，但实验条件往往与自然相去甚远。这项研究将首次将现场收集的咬合行为和咬合力数据与实验室进行的生物力学实验相结合。第一个目的是研究不同咬合方式如何对头骨施加载荷以及这些载荷是如何分配的。通过比较物种内不同咬合方式施加的载荷机制，将确定常规咬合行为与形态之间的因果联系。第二个目标是解决与哺乳动物进食有关的另外两个悬而未决的问题：头骨形状在多大程度上受到其他感官系统(在这种情况下是视觉)的限制，以及面部骨骼相对于进食过程中产生的力量的强度。这些问题的答案可能解释了为什么某些哺乳动物的谱系表现出比其他种类更多样的头骨形状。最初，将测量咬合产生的力，并在野外记录哺乳动物的进食行为。接下来，将在实验室使用有限元(FE)建模和分析来研究这些行为的力学含义，有限元建模和分析是工程师广泛使用的基于物理的数值技术，用于评估物理系统的力学行为。有限元分析(FEA)为形态-功能关系提供了一个真正新颖的视角，但大多数生物学家还不能接触到。一个目标是通过实现两个具体的方法学目标来使有限元分析更容易进行：1)确定哺乳动物头骨的有限元模型可以简化的程度，并且仍然可以产生足够准确的结果；2)开发有效地将CT扫描转换为三维有限元模型的协议。这些结果将通过同行评审的科学出版物、演示文稿和研讨会传达给生物界。功能解剖学家和机械工程师之间的这种合作提供了一个极好的机会来培训研究生，并让本科生接触到生物力学、比较解剖学和机械工程方面的协作、跨学科研究。研究生研究助理将进行他们自己的原创研究，并帮助PI指导4-6个本科生研究项目。这些项目将成为生物和/或工程学研究生学习的跳板。

Biting Style and the Biomechanics of Feeding in MammalsElizabeth R. Dumont (PI), Ian R. Grosse (Co-PI)University of Massachusetts, AmherstThe evolutionary history of mammals is largely a story about exploiting an ever broader array of food resources. While the first mammals were insect-eaters, modern mammals specialize in diets ranging from insects to fruits, foliage, meat, and plankton. This diversity in diet is reflected in the shape of the skull - the primary 'tool' that mammals use to bite and chew food. Importantly, however, the underlying mechanism driving the evolution of this diversity is unknown. This study explores the importance of the biomechanical link between the forces generated during biting and the anatomy of mammal skulls that safely and optimally bear and disperse these forces. Further, this study investigates the role of this relationship in the evolution of diversity in skull shape.Previous analyses of mammalian feeding have taken one of two approaches, each of which has inherent limitations. Broad comparative studies document correlations between skull shape and diet, but fall short of testing the causal mechanisms underlying the correlations. On the other hand, detailed experimental studies document how bones and muscles behave during feeding, but the experimental conditions are often far from natural. This study will be the first to combine data on biting behavior and bite force gathered in the field with biomechanical experiments carried out in the laboratory.The first aim is to investigate how different biting styles apply loads to the skull and how those loads are dispersed. Causal links between routine biting behaviors and morphology will be identified by comparing the loading regimes imposed by different biting styles within species. The second aim is to address two other unresolved issues regarding feeding in mammals: the extent to which skull shape is limited by other sensory systems (in this case, vision), and the strength of the facial skeleton relative to forces generated during feeding. Answers to these issues may explain why some lineages of mammals exhibit a wider variety of skull shapes than do others. Initially, the forces generated by biting will be measured and the feeding behavior of mammals will be documented in the field. Next, the mechanical implications of these behaviors will be investigated in the laboratory using finite element (FE) modeling and analysis, a physics-based numerical technique widely used by engineers to assess the mechanical behavior of physical systems. FE analysis (FEA) provides a truly novel perspective on form-function relationships, but is not yet accessible to most biologists. An objective is to make FEA more accessible by accomplishing two specific methodological aims: 1) determine the extent to which FE models of mammal skulls can be simplified and still yield sufficiently accurate results, and 2) develop protocols for efficiently translating CT-scans into three dimensional FE models. These results will be communicated to the biology community through peer-reviewed scientific publications, presentations, and workshops. This collaboration between a functional anatomist and a mechanical engineer offers an excellent opportunity to train graduate students and to expose undergraduates to collaborative, interdisciplinary research in biomechanics, comparative anatomy, and mechanical engineering. Graduate Research Assistants will conduct their own original research, and help the PIs to mentor 4-6 undergraduate research projects. These projects will serve as a springboard to graduate studies in biology and/or engineering.