Exploratory Analysis and Three Dimensional Characterization of the Terrestrial Locomotion of South American Sea Lions (Otaria flavescens)

Abstract

This study aimed to characterise the three-dimensional terrestrial locomotion of male and female South American sea lions (Otaria flavescens), with particular emphasis on their spatiotemporal organisation and three-dimensional body and limb movements. Two females and one male were recorded during the half-bound gait using a four-camera system, allowing the trajectories of six anatomical landmarks (Eye, the cranial part of the carpus (“Wrist”), the tip of digit I and digit V of the forelimb (respectively “F1” and “F5”), the tip of digit I of the hindlimb (“H1”), and the caudal part of the tarsus (“Ankle”)) to be analysed throughout the locomotor cycle. The results showed a relatively consistent spatiotemporal organisation of locomotion among individuals, with mean speeds ranging from 2.01 to 2.31 BL/s and cycle frequencies from 1.25 to 1.66 Hz. However, individual differences were observed in hindlimb use: H1 was not used as a supporting point by the male, whereas it remained in contact with the substrate in both females. The three-dimensional analysis revealed substantial vertical and lateral oscillations, particularly for the Eye and H1, while F1 and Ankle generally exhibited smaller vertical ranges. Head movement also included a marked horizontal component, suggesting a more complex three-dimensional trajectory than the vertical head bobbing previously described in California sea lions. Overall, this study provides a first three-dimensional description of terrestrial locomotion in O. flavescens and demonstrates the relevance of considering movements outside the sagittal plane. Although the limited number of individuals prevents firm conclusions regarding sexual differences, the observed individual variability provides a basis for future studies involving larger samples, additional species, and other locomotor gaits.