Meeting Abstract
The integration of experimental data and modelling techniques have generated novel hypotheses about the fin-to-limb transition. One such hypothesis suggests that early tetrapods were incapable of salamander-like walking gaits. However, some dipnoans are well-known for their propensity for underwater walking. As such, it is possible that the neuromuscular substrates for quadrupedal gaits did not evolve during the invasion onto land, but instead for movement on benthic substrates. If true, living salamanders may be too anatomically derived to be particularly informative about the locomotor patterns of early tetrapodomorphs. In this study, we collect limb-loading data and three-dimensional femoral kinematics using X-ray Reconstruction of Moving Morphology from the West African lungfish (Protopterus annectens) during underwater walking. These data are compared to patterns of terrestrial locomotion in three species of salamander. Limb-loading in lungfish is dramatically lower than predicted based on their body mass, presumably due to the lungs providing additional buoyancy. However, when scaled to the underwater mass of the animal, limb-loading patterns and magnitudes are comparable to salamanders. Movements and overall excursion of femoral protraction/retraction and abduction/adduction are similar between walking lungfish and salamanders. However, long-axis rotation of the femur is substantially lower during quadrupedal walking in lungfish. These findings suggest that despite limited long-axis rotation of the femur, as has been posited for some stem tetrapods, quadrupedal gaits and tetrapod-like limb loading patterns can be achieved.
