Developmental Plasticity and the Origin of Tetrapods (video) McGill University Share Print E-Mail Loading video... Caption Polypterus senegalus walks across a sandy substrate. Fish use their fins and body in combination to move across a terrestrial substrate. Fins are planted one after the other to lift the head and anteriobody and the tail and body are used to push the fish forward over the planted fin. Credit E.M. Standen and T.Y. Du, H. Larsson Usage Restrictions Please credit Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.