New ‘S-Start’ Locomotion Discovered in Yellow Anacondas
The discovery of a new escape movement in newborn yellow anacondas has expanded our understanding of limbless locomotion. Known as the ‘S-start’, this motion is a rapid, non-planar movement used by the snakes to flee threats. An international team of researchers including experts from the USA and India documented and modelled this unique behaviour. The study offers fresh vital information about snake evolution and could inspire advances in soft-bodied robotics.
Recent Discovery of the ‘S-Start’ Escape Movement
Newborn yellow anacondas use a previously undocumented escape movement. When threatened, they lift their heads slightly and coil into an ‘S’ shape. This S-curve travels down the body, propelling the snake forward quickly. Unlike common snake locomotion, this motion is transient and energetically costly. It is used only briefly to escape danger before resetting for another attempt.
Traditional Snake Locomotion Types
Snake movement is generally classified into three types – rectilinear crawling, undulatory motion, and sidewinding. Rectilinear crawling involves straight-line movement. Undulatory motion is wave-like bending of the body. Sidewinding is a specialised movement seen in desert snakes. The S-start does not fit into these categories, showing that snake locomotion is more diverse than previously thought.
Scientific Modelling of the Motion
Researchers modelled the snake’s body as a flexible, active filament to simulate the S-start. The challenge was to replicate internal forces and torques that produce the complex posture. Surprisingly, just three localised torque pulses moving along the body recreated the motion. The model combined in-plane and out-of-plane bending to capture the snake’s lifting and twisting actions.
Muscle Strength and Juvenile Advantage
The S-start requires a high muscle-to-weight ratio. Juvenile yellow anacondas are light and muscular enough to perform this energy-intensive movement. Adult snakes are too heavy or lack the required muscle strength. The model’s phase space maps conditions under which the S-start is possible, explaining its restriction to young snakes.
Evolutionary Links to Sidewinding
Repeated S-start movements evolved into sidewinding in simulations. Sidewinding is a smooth, efficient locomotion used by desert snakes. This suggests an evolutionary connection between the two motions. Other snake movements, like the lasso motion in tree climbers, might be variants of the S-start. Further research is needed to confirm these evolutionary pathways.
Implications for Robotics and Biology
The study bridges gaps in snake locomotion classification and marks the role of transient escape movements. These brief, rapid motions are vital for survival. Understanding the S-start can guide the design of robots that move in complex three-dimensional ways. The elastic filament model may be extended to other limbless species, aiding the development of versatile soft-bodied robots.
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