Torque limitations on cantilevering in <i>Dendrelaphis</i> snakes

Arboreal animals face potentially substantial torques when reaching across gaps, which may limit the size of the gap they can cross with non-dynamic behaviors. Snakes can experience particularly large torques during gap crossing, because they must counteract both pitching and buckling torques while extending into the gap in a cantilever-like posture. Pitching and buckling limits may impose different constraints on gap-crossing locomotion, but their relative importance remains unclear. To investigate this problem, we analyzed kinematic and morphological data related to gap crossing in Dendrelaphis snakes, complemented by data from their sister taxon, Chrysopelea, to test predictions from a theoretical model of cantilever failure. Specifically, we evaluated whether the existing model of buckling predicts maximum observed cantilever performance in these snakes, and compared those predictions with pitching limits estimated from body mass distributions. The buckling model produced estimates far below observed cantilever extents, even across plausible ranges of tendon ratio and multi-articular span, indicating that the current model does not yet capture the mechanics of buckling in cantilevering snakes. By contrast, snakes switched to dynamic movements close to their theoretical pitching limit, supporting the idea that pitching torques constrain cantilever abilities. These results suggest that pitching torque is a major constraint on cantilever-based gap crossing, while also identifying the need for improved buckling models with higher anatomical fidelity. More broadly, this study shows how testing mechanical models against behavior can reveal both the limits shaping locomotor performance and the limitations of existing models.