BIOMECHANICAL ANALYSIS OF STYLOPHORAN (PHYLUM ECHINODERMATA) MOTION

The body plan of the extinct echinoderm class Stylophora, which consists of a flat, large body and thin flexible ‘tail’, is structurally unique. As such, the physiology of stylophorans has puzzled paleontologists since they were first discovered. Of particular interest is the mechanics underlying locomotion. Movement is an expected stylophoran capability, due to differential positioning of articulated tails (the aulacophore) in fossil specimens, the occurrence of ichnofossils directly associated with preserved individuals, and the lack of a holdfast that would have stabilized the organism if it were sessile. However, due to the non-analogous nature of the body plan, the mechanics behind movement and locomotion in this group are not immediately apparent. Many hypotheses have been suggested, including swimming and several strategies for crawling, but there has not been a satisfactory way to test them. Recent advances in biotechnology offer a platform for exploring the biomechanics of fossil organisms. In this study, 3D musculoskeletal models of stylophorans were generated using SIMM (Software for Interactive Musculoskeletal Modeling) and used to study their locomotion. The models were built by importing micro-CT scans of specimens into the software, and virtually recreating joint and muscular infrastructure to reconstruct the musculoskeletal system. The range of motion of the stylophoran aulacophore can be constrained by analyzing the morphology of articulated specimens within the SIMM models. This results in the first biomechanically rigorous prediction of the movement capabilities that permitted locomotion in the group.