Meeting Abstract
Becoming terrestrial was a pivotal event in vertebrate evolution that placed new physical demands on the musculoskeletal system. Increased gravitational loads on land can make bones more prone to injury, but how stressful was terrestrial locomotion for early tetrapods? We used a computational model to estimate the magnitude of peak bone stresses, across limb postures ranging from hyper-sprawling to upright, by integrating experimental data from live animals with morphological data from fossils. Although salamanders are often used to model some of the earliest tetrapods due to their generalized tetrapod Bauplan, they may better represent stages that occurred later in the transition to land. Our laboratory studies show that a semi-aquatic salamander (Pleurodeles waltl) had a hyper-sprawled limb posture compared to the terrestrial tiger salamander (Ambystoma tigrinum), with ground reaction forces intermediate between semi-aquatic mudskipper fish and terrestrial A. tigrinum. When these data were used in our computational model of a crownward early tetrapod (Greererpeton burkemorani) using a salamander-like gait, femoral stresses decreased as the limbs became more sprawled. Moreover, stresses were lower when Greererpeton was modelled with limb mechanics resembling those of salamanders rather than alligators, supporting salamanders as a reasonable model for Greererpeton. Our results also indicate that the estimated peak stresses on the Greererpeton femur never exceeded typical values of ultimate bending strength for amphibian limb bones, suggesting appendicular bones were likely well suited for terrestrial locomotion relatively early in their evolution. These analyses set the stage for further evaluations of limb posture and terrestrial locomotor capacity across the water-to-land transition.
