BIOFLow International Research Experience for Students (IRES)

Hydrodynamics of underwater walking in early tetrapods


While the first steps onto land were one of the greatest evolutionary transitions in animals, walking first arose underwater for movement along the submerged substrate, and was used in this manner long before being co-opted to terrestrial locomotion [1–3]. However, in spite of the evolutionary importance of underwater walking, our knowledge is mostly limited to descriptions of movement patterns [4–7], with the minimal study of either the mechanical forces or how animals control their interactions (i.e. dynamics) to produce effective locomotion.

The forces governing underwater walking represent a mix of those seen in pelagic swimming and terrestrial walking.  Like pelagic swimming, the bodyweight nearly completely supported by buoyant force and hydrodynamic drag opposes forward motion, but, like in terrestrial walking, forward propulsive force is generated the limbs pressing against the substrate.

Dr. Astley’s lab is currently working on a mechanism to measure the substrate reaction forces during underwater walking in a model species, the axolotl (Ambystoma mexicanum).  This additional project would explore the hydrodynamics of this movement, including estimating overall body drag, the contribution of limb movements, and the role of the added mass effect.

​​​​​​​IRES student involvement

Dr. Astley will work with an IRES student. The IRES student will reconstruct a model of our axolotls and determine basic hydrodynamic parameters, namely drag and added mass effect, as well as modeling the influence of limb motion of these parameters.


  1. Clack JA. Gaining Ground: The Origin and Evolution of Tetrapods. Bloomington: Indiana University Press; 2002. 369 p.
  2. Edwards JL. Two Perspectives on the Evolution of the Tetrapod Limb. Am Zool [Internet]. 1989 Feb 1 [cited 2019 Jan 25];29(1):235–54. Available from:
  3. Eaton TH. The Aquatic Origin of Tetrapods. Trans Kansas Acad Sci [Internet]. 1960 [cited 2019 Jan 25];63(3):115. Available from:
  4. Pridmore PA. Submerged walking in the epaulette shark Hemiscyllium ocellatum (Hemiscyllidae) and its implications for locomotion in rhipidistian fishes and early tetrapods. Zoology. 1994;98(95):278–97. K.S. Sheldon, L. Zhao, A. Chuang, I. N.
  5. Martinez MM, Full RJ, Koehl MA. Underwater punting by an intertidal crab: a novel gait revealed by the kinematics of pedestrian locomotion in air versus water. J Exp Biol [Internet]. 1998;201(18):2609. Available from:
  6. Ashley-Ross MA, Lundin R, Johnson KL. Kinematics of level terrestrial and underwater walking in the California newt, Taricha torosa. J Exp Zool Part A Ecol Genet Physiol [Internet]. 2009;311A(4):240–57. Available from:
  7. Macesic LJ, Kajiura SM. Comparative punting kinematics and pelvic fin musculature of benthic batoids. J Morphol [Internet]. 2010;271(10):1219–28. Available from: