Sharks That Walk On Land PDF Download

Abstract: Aquatic and terrestrial environments exhibit physical disparities that introduce contrasting challenges to vertebrate locomotion. Extant vertebrates with amphibious capabilities provide valuable study systems to test functional hypotheses on how organisms modulate their locomotion between environments. One species of cartilaginous fish, the epaulette shark (Hemiscyllium ocellatum), moves between aquatic and terrestrial environments and uses a diagonal sequence “walking-trot” that resembles the locomotion of salamanders, a common model for the water-land transition in vertebrate evolution. I quantified the locomotor kinematics of H. ocellatum while in a fully submerged and partially emerged environment, and then compared the findings to published data on salamander walking to investigate the role of fins vs. limbs when performing a similar gait. These data suggest that the epaulette shark relies primarily on appendage-based locomotion across both environments and produces ~50–70% more angular movement in the pelvic girdle compared to the pectoral girdle. The pelvic fin produces ~15–25% more angular movement compared to the pelvic fin while they are being adducted. The pelvic fin also adducts more when in a partially emerged condition, while the pectoral fin tends to show greater abduction when partially emerged out of water compared to fully submerged trials. Hemiscyllium ocellatum exhibits minimum lateral bending between the girdles and a lower range of girdle angles when compared to salamander walking on land which may limit stride length and, therefore, forward movement across environments. Yet, H. ocellatum retains a duty factor representative of a walking gait between environments. In this study, I have quantified differences in the roles of fins vs. limbs in a diagonal sequence gait and describe how the biomechanics of H. ocellatum may be a more appropriate model for studying the locomotor capabilities of stem tetrapods that still resemble their more fish-like ancestors.