The elephant proboscis (trunk), which functions as a muscular hydrostat with a virtually infinite number of degrees of freedom, is a spectacular organ for delicate to heavy objects manipulation as well as social and sensory functions. Using high-resolution motion capture and functional morphology analyses, we show here that elephants evolved strategies which reduce the biomechanical complexity of their trunk. Indeed, our behavioural experiments with objects of various shapes, sizes and weights indicate that (i) complex behaviours emerge from the combination of a finite set of basic movements, (ii) curvature, torsion and strain provide an appropriate kinematic representation, allowing to extract motion primitives from the trunk trajectories, (iii) transport of objects involves the proximal propagation of an inward curvature front initiated at the tip, (iv) the trunk can also form pseudo-joints for point-to-point motion, and (v) the trunk tip velocity obeys a power law with its path curvature, similar to human hand drawing movements. We also reveal with unprecedented precision the functional anatomy of the African and Asian elephant trunks using medical imaging and macro-scale serial sectioning, thus drawing strong connections between motion primitives and muscular synergies. Our study is the first combined quantitative analysis of the mechanical performance, kinematic strategies and functional morphology of the largest animal muscular hydrostat on Earth. It provides data for developing innovative ‘soft-robotic’ manipulators devoid of articulations, replicating the high compliance, flexibility and strength of the elephant trunk.
This website contains supplementary material for the research article:
‘Elephants evolved strategies reducing the biomechanical complexity of their trunk’
Paule Dagenais, Sean Hensman, Valérie Haechler and Michel C. Milinkovitch
Current Biology, Vol. 31, (August 2021)
https://doi.org/10.1016/j.cub.2021.08.029
Experiments were conducted in collaboration with Adventures with Elephants: https://adventureswithelephants.com
More information about how these results can inspire the design of an innovative soft robot: https://proboscis.eu