HYDROSTATIC LOCOMOTION IN A LIMBLESS TETRAPOD

Caecilians are an ancient and enigmatic group of limbless, burrowing a mphibians found throughout most of the humid tropics(1,2). Over the pa st 100 million years, the majority of caecilian lineages seem to have retained a series of highly derived musculoskeletal traits from a comm on ancestor. Among these features are unusually oriented body wall mus cles' and a vertebral column that moves independently of the skin(4-9) . Until now, these strange characteristics have defied a satisfying fu nctional explanation. Our data suggest that the unique morphology of c aecilians enables them to power locomotion hydrostatically by applying force to a crossed-helical array of tendons that surrounds their body cavity. Using this system, the Central American Dermophis mexicanus c an generate approximately twice the maximum forward force as similar-s ized burrowing snakes that rely solely on longitudinally oriented musc ulature of the body wall and vertebral column for forward force produc tion. Although many groups of invertebrates use hydrostatic systems to move(10-13) and many vertebrates use hydrostatic systems in localized body parts(13-14), caecilians are the first vetebrates known to use t he entire body as a hydrostatic system for locomotion.