The robotic approach to the passive interlocking mechanism in the hindlimb musculoskeletal system of Crocodylus porosus.

Efficient locomotion in terrestrial vertebrates relies on intra-limb coordination that emerges through interaction with the environment and passive interlocking of the musculoskeletal system. These structures have been well investigated in some mammals and birds, but the presence of similar structures in other terrestrial vertebrates has been under appreciated. This study addresses the functionality of the passive interlocking system in reptilian hindlimb locomotion by dissecting Crocodylus porosus and constructing a robot. Based on the dissection, we hypothesized that the passive interlocking mechanism consisted of multiple muscles to maintain the semi-erect limb posture and support its weight. The mechanism is provided by the caudifemoralis longus muscle, along with its tendon and the gastrocnemius externus, acting as a passive element that interacts with the ground reaction force. Accordingly, the feasibility of the interlocking function was demonstrated by a robot implementing the hindlimb and pelvic musculoskeletal system of crocodilians. This study provides new insights into the locomotion mechanism of crocodilians and emphasizes the importance of passive interlocking in efficient locomotion in terrestrial vertebrates. The findings could have implications for developing biomimetic robots and understanding the evolution of terrestrial locomotion in vertebrates. [ABSTRACT FROM AUTHOR]