First Steps: The Dynamics and Control of Underwater Walking

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The colonization of land by animals is one of the greatest evolutionary events in the history of life, but our understanding of the physics of this occurrence is limited. Long before animals walked on land, the first steps were taken beneath the water's surface by animals walking on submerged substrates. This behavior formed the basis for eventual movement on land, but the physics display a complex mix of fluid forces (drag, buoyancy) and typical walking forces (foot-substrate interactions, gravity). Understanding of this behavior is limited by the inability to effectively measure the forces exerted on the substrate. This project will create a custom-designed force sensing system to record the small substrate forces that occur during underwater walking, and, combined with measurements of drag, buoyancy, and other fluid forces, will provide the first complete picture of the mechanics of this behavior. This will provide crucial insights into the evolution of walking and how animals adapted to the eventual transition onto land. In addition to providing valuable training for graduate students, this project will provide the scientific community with a new tool for investigating underwater forces and provide insights for the design of biologically-inspired underwater exploration vehicles.Effective locomotion was crucial to the initial invasion of land, and underwater walking was the key behavioral predecessor that was exapted into terrestrial use during this transition. However, the biomechanics and control of underwater walking are poorly known, in part due to the difficulty of measuring small substrate reaction forces. The combination of both fluid and substrate forces could make typical walking dynamics untenable, particularly the reduced effective body weight due to buoyant support, and damping effects from the surrounding fluid (particularly drag and the added mass effect). This project will investigate the dynamics and control of underwater walking via direct measurement of substrate reaction forces using a novel underwater force sensing system, combined with measurements of fluid forces, across variable substrates and environmental conditions. This will provide insights into how these forces interact and how animals control these interactions to produce controlled locomotion, as well as how changes in environment could affect these dynamics and how underwater walking could be exapted to a terrestrial setting. Effective understanding of these dynamics could provide insight into the use of underwater walking in extant species, the biomechanics of the ancient transitions from underwater to terrestrial walking, and insight into the control of underwater walking robotic systems for exploration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.