Salamanders are often used as representatives of the basal tetrapod body plan in functional studies. However, little is known about the loads experienced by their limb bones during locomotion; previous studies of bone loading have focused mainly on animals such as mammals and birds with parasagittal limb posture. This study evaluates the loads on the limb bones of the tiger salamander (Ambystoma tigrinum) during terrestrial locomotion using three-dimensional measurements of the ground reaction force (GRF) and hindlimb kinematics, as well as anatomical measurements of the femur and hindlimb muscles. Peak GRFs acting on a single limb were about half the body weight of the salamander. The GRF is initially oriented posteriorly but shifts to an anterior direction later in the step, and has very little medio-lateral inclination. At the time of peak stress, the GRF is primarily vertical and perpendicular to the femur. Peak stresses were generally below 15 MPa, which is fairly low compared to observations from other vertebrate lineages. The peak stress was primarily associated with dorso-ventral bending, which may be partially due to a lack of activity in knee extensor muscles that span the length of the femur. Using mechanical property values collected from hardness tests, we calculated a safety factor exceeding 10. Together with data from other amphibian and reptile lineages, these results suggest that low magnitude loading and high limb bone safety factors may have an ancient evolutionary history. Supported by NSF (IOB-0517340).
Available at: http://works.bepress.com/megan_sheffield/10/