Comparing submerged walking and swimming kinematics in epaulette sharks

{Extract} The transition from swimming to walking was an important event in the evolution of tetrapods. To understand this transition, researchers have studied movement in many extinct and extant aquatic and semi-aquatic species. The epaulette shark Hemiscillum ocellatum uses slow-to-medium walking, fast walking, and swimming forms of aquatic locomotion. We described kinematic differences between the three gaits in neonate (n=6) and juvenile (n=6) sharks hatched and reared in the laboratory. Neonates retain nutrition from an internal yolk until they develop a consistent feeding schedule (~35d post-hatch). They are then classified as juveniles, foraging for worms, crustaceans, and small fish. We hypothesized that changes in diet and feeding habits would affect gait performance between neonates and juveniles. Using video tracking software and 13 anatomical landmarks along the fins, girdles, and body mid-line, whole body velocity, duty factor, fin frequency, girdle rotation, and body curvature were calculated to identify characteristic movements of the gaits for each shark. Velocity was greater in neonates when compared to juveniles across all gaits; however, both groups increased velocity from walking to swimming. Regardless of gait, pelvic girdles had a greater range of motion than pectoral girdles for both neonates and juveniles. In juveniles, regardless of gait, the contralateral sides of the pectoral and pelvic girdles were synchronized during lateral excursions. Neonates, however, exhibited overlapping of ipsilateral sides of the girdles. Understanding the transition from neonate to juvenile locomotory forms in this species could provide insight on the water to land transition of tetrapods