Meeting Abstract
Many existing organisms use flipper-like limbs for both aquatic and terrestrial locomotion. In the transition from an aquatic to a terrestrial environment, early tetrapod walkers adapted to the challenges of locomotion on complex substrates (e.g. sand and mud), which can exhibit both solid and fluid-like properties. Laboratory studies of physical robot models reveal that locomotor performance on dry granular media is sensitive to variations in limb morphology and kinematics. Although previous studies have reconstructed skeletal morphologies of early walkers, the impact of kinematics on their locomotor performance, particularly the importance of the tail, remains unclear. To gain insight into how early walkers contended with complex substrates, we developed a flipper-driven physical robot model with limb-joint morphology inspired by the mudskipper fish (Oxudericinae), a model analog for early tetrapod walkers. We discovered that although mudskippers move effectively on level substrates with a crutching gait driven by their front fins, their locomotor ability becomes limited as substrate tilt is increased, unless they use their well-developed tails to prevent slipping and generate forward thrust. The addition of an actuated tail to the robot improved performance, simplifying the robot’s control strategy: tail use made the robot more robust to variations in morphology and kinematics, such as flipper tilt and flipper insertion depth, and made locomotion on inclines possible for morphological configurations that otherwise failed. With these discoveries, we are elucidating a minimal feature set that would have allowed the first terrestrial vertebrates to adapt to life and locomotion on complex terrestrial environments.
