Tail deflection but not bending varies with speed in lizards: results from an automated tracking analysis pipeline

R Scripts and data sheets used for the multi-species study on tail and spine biomechanics among lizards. Abstract: Tail movement is an important component of vertebrate locomotion, and likely contributes to dynamic stability during steady-state locomotion. Previous results suggest that the tail plays a significant role in lizard locomotion, but little data are available on tail motion during locomotion and how it differs with morphological, ecological, and phylogenetic parameters. We collected high-speed vertical climbing and horizontal locomotion video data from 43 lizard species from 4 taxonomic groups (Agamidae, Gekkota, Scincidae, Varanidae) and 4 habitats. We introduce a new semi-automated and generalizable analysis pipeline for tail and spine motion analysis including markerless pose-estimation, semi-automated kinematic recognition, and muti-species data analysis. We found that step length relative to SVL increased with tail length relative to SVL. Examining spine cycles agnostic of limb stride phase, we found that ranges of inter-tail bending compared to inter-spine bending increased with relative tail length while ranges of tail deflection relative to spine deflection increased with relative speed. Considering stepwise strides, we found that the angular amplitude of the tail center of mass decreased with relative speed while its angular velocity and acceleration increased with relative speed. These results will provide general insights into the biomechanics of tails in sprawling locomotion enabling biomimetic applications in robotics, and a better understanding of vertebrate form and function. We look forward to adding more species, behaviors, and locomotor speeds to our analysis pipeline through collaboration with other research groups.