| Natural environments offer constant challenges to locomotion since it is filled with obstacles to circumvent, predators to escape, and prey to capture. Locomotor surfaces also vary widely in stiffness such that the maintenance of stability in the real world can often be difficult. This dissertation explores how animals are able to maintain stability when they are already inherently unstable by studying two phenomena: the fantastic bipedal water-running ability of the basilisk lizard (a.k.a. the "Jesus Christ" lizard) and the extraordinary high-speed terrestrial and aerial locomotor feats of a small, amphibious fish, the Pacific leaping blenny. High-speed videography was used to quantify the motion of both of these animals. All two-dimensional data were transformed into three dimensions using direct linear transformation or image processing algorithms to correct for lens distortions. Digital particle image velocimetry, a technique traditionally used for measuring force production underwater, was then used to directly measure the forces produced by water-running lizards at the air-water interface. Finally, a novel force platform using optical sensors as strain gauges was designed and built to measure the millinewton forces produced by the amphibious blennies as they jumped. Results showed that when running on a yielding surface such as water basilisks traced complex, three-dimensional paths through the water, generating large medio-lateral forces (37-79% body weight) with each step. These forces are likely used to maintain stability when using an unstable surface such as water as a locomotor surface. In contrast, the Pacific leaping blenny does not have limbs or any obvious modifications to its external morphology that would afford it an advantage over its fully-aquatic sister taxa for moving about on land. Kinematic and kinetic results showed that the Pacific leaping blenny performs a novel axial tail twisting behavior that allows it to push off surfaces with the larger, lateral tail surface rather than the narrow, ventral tail edge. This kinematic innovation permits it greater control and stability when executing land-based jumps. |
