Meeting Abstract

S3-2.3  Saturday, Jan. 5  Comparative appendicular function during terrestrial locomotion: implications for the invasion of land KAWANO, S.M.*; BLOB, R.W.; Clemson Univ.; Clemson Univ.

The invasion of land was a pivotal event in vertebrate evolution that was associated with major appendicular modifications. Although fossils indicate that the evolution of fundamentally limb-like appendages may have occurred in aquatic environments, the functional consequences of using early limbs, rather than fins, for terrestrial propulsion have had little empirical investigation. Moreover, while many fossil specimens have indicated that terrestrial adaptations first arose anteriorly in tetrapodomorphs, some experimental data have suggested a greater antiquity to “hindlimb driven” locomotion. To examine these aspects of vertebrate locomotor evolution during the invasion of land, we measured three-dimensional ground reaction forces (GRF) produced by isolated pectoral fins of mudskipper fishes (Periophthalmus barbarus) during terrestrial crutching and compared these to isolated walking footfalls by the fore- and hindlimbs of tiger salamanders (Ambystoma tigrinum). As a proportion of body weight, isolated fins of mudskippers bear similar peak net GRF magnitudes as salamander limbs, but fin GRFs are inclined more medially. Comparing salamander fore- and hindlimbs, although the peak net GRF occurs later in stance for the forelimb, both limbs experience nearly identical mediolateral and vertical GRF components, suggesting they make comparable contributions to support. Thus, a major locomotor role for the forelimb may have persisted extensively among basal tetrapods. However, the salamander forelimb was typically deceleratory at peak GRF, whereas the hindlimb and mudskipper pectoral fin were mainly acceleratory. Together, data from these extant taxa help clarify how structural change may have influenced locomotor function through the evolutionary invasion of land by vertebrates.