DISSERTATION RESEARCH: Mechanical Properties and Functional Morphology of Mammalian Footpads

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Dr. Virginia L. Roth & Kai-Jung ChiFootpads are found universally in terrestrial mammals; however, how footpads function during locomotion is poorly understood. At each step, footpads are believed to cushion impact, stabilize the foot, and return elastic energy. To perform all these roles, the pad must have the paradoxical properties of being compliant and stiff, resilient and damped. This study proposes a solution to this apparent paradox- the footpad has mechanical anisotropy. This hypothesis has been supported by results on plantigrade footpads in the context of locomotion, and will be tested on two lineages that evolved digitigrady separately: cats and dogs. Furthermore, this study also proposes to identify the morphological determinants that explain footpads' mechanical variation observed both intra- and interspecifically. Mechanical and morphological parameters measured on each species will be compared to examine whether footpad properties reflect locomotor habits as suggested in previous studies. The goals of this study will be achieved by three approaches: (1) Investigation of foot kinematics and mechanical roles of footpads in moving digitigrade mammals, (2) Measurement of compressive and shear properties of isolated footpads both statically and dynamically, and (3) Examination of the compositional and structural morphology of footpads. This study will provide the first experimental and comparative analysis of mechanisms of footpad function, especially in the context of locomotion. Such an integrative study will lay the framework for future work focused on structure and function of pads in animals less tolerant of laboratory conditions, and on scaling, adaptation, diversity, and evolution of mammalian feet and footpads.