A comparative analysis of the novel terrestrial locomotion of the tidepool sculpin, Oligocottus maculosus

Abstract

Tidepool sculpins (Oligocottus maculosus) are intertidal fish that use a novel mode of terrestrial locomotion to traverse their semi-terrestrial environment. Our goals were to describe the kinematics of the terrestrial locomotion of O. maculosus and compare their terrestrial locomotion to their aquatic locomotion, the terrestrial locomotion of subtidal sculpin species (Leptocottus armatus and Icelinus borealis), and the terrestrial locomotion of walking catfish (Clarias spp.). We used high-speed video to record locomotion on a terrestrial platforms and in water, and landmark tracking software in MATLAB to analyze their locomotion. O. maculosus use a novel form of axial-appendage-based locomotion, driven by lateral oscillations of the tail synchronized with alternating rotation about the base of their pectoral fins, described as an “army crawl”. Unlike Clarias spp., which use a diagonal gait, O. maculosus use a lateral gait. The army crawl likely originates from a modified series of aquatic fast starts in a terrestrial environment. However, they use axial undulation of the body during aquatic locomotion, whereas they use axial oscillation and pectoral fins in terrestrial locomotion. The army crawl is more effective at moving linearly on land than the terrestrial “wiggle” used by subtidal sculpins. It is possible that the earliest vertebrates on land used forms of terrestrial locomotion analogous to the terrestrial locomotion of fishes. Actinopterygians like O. maculosus may have begun the transition onto land before the rise and terrestrial success of sarcopterygians by using behavioral adaptions, which would not show in the fossil record like morphological adaptations.