Doctoral Dissertation Research: The Biomechanical Evolution of Echinoderm Locomotion

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Brittle stars, close relatives of sea stars, move in a different manner from all other mobile animals. Their arms consist of hundreds of moving parts. As a result, brittle stars can travel rapidly in any direction. They also easily adapt their method of locomotion in response to limb damage and loss. This project will identify the mechanical steps that characterize the evolution of this unique pattern of locomotion. Fossil brittle stars show much greater diversity of arm structure than living brittle stars, making interpretation of their mode of locomotion a challenge. These researchers will characterize the anatomy of fossil brittle stars using 3D imaging and infer their movement capabilities based on biomechanical modeling. This is the first project to employ state-of-the-art 3D imaging and biomechanical modeling techniques to study the mechanics of movement in any non-vertebrate animal. A broader impact of this research is that it opens the door for the systematic investigation of diverse movement strategies across the animal kingdom and their application to mechanical engineering. The unique movement strategy employed by these animals may also help improve robot design. The first step in modeling brittle star movement is to digitize their internal skeleton using 3D x-ray imaging. A computer program is then used to make a skeletal model and to reconstruct movement at the articulations. Muscle attachment sites are identified in the fossils using high-resolution 3D imaging; the microstructure of the skeleton reveals where muscles insert. A second program is used to incorporate the muscle reconstructions into the skeletal models. The force applied by each arm segment and by the entire arm can be calculated to reveal whether fossil brittle stars could move like their modern relatives, or used a different strategy more similar, for example, to that in living sea stars. These models will allow the mechanical steps leading to the unique form of movement in living brittle stars to be determined, and show how their mode of locomotion evolved.