Kavli Affiliate: L. Mahadevan
| First 5 Authors: N. Charles, R. Chelakkot, M. Gazzola, B. Young, L. Mahadevan
| Summary:
Of the vast variety of animal gaits, one of the most striking is the
non-planar undulating motion of a sidewinder. But non-planar gaits are not
limited to sidewinders. Here we report a new non-planar mode used as an escape
strategy in juvenile anacondas (Eunectes notaeus). In the S-start, named for
its eponymous shape, transient locomotion arises when the snake writhes and
bends out of the plane while rolling forward about its midsection without
slippage. To quantify our observations, we present a mathematical model for an
active non-planar filament that interacts anisotropically with a frictional
substrate and show that locomotion is due to a propagating localized pulse of a
topological quantity, the link density. A two-dimensional phase space
characterized by scaled body weight and muscular torque shows that relatively
light juveniles are capable of S-starts but heavy adults are not, consistent
with our experiments. Finally, we show that a periodic sequence of S-starts
naturally leads to a sidewinding gait. All together, our characterization of a
novel escape strategy in snakes highlights the role of topology in locomotion,
provides a phase diagram for mode feasibility as a function of body size, and
suggests a role for the S-start in the evolution of sidewinding.
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