Slick and Slender Snake Beats Short and Stubby Lizard in Sand Swimming

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Newswise For swimming through sand, a slick and slender snake can perform better than a short and stubby lizard.

Thats one conclusion from a study of the movement patterns of the shovel-nosed snake, a native of the Mojave Desert of the southwest United States. The research shows how the snake uses its slender shape to move smoothly through the sand, and how its slippery skin reduces friction both providing locomotive advantages over another sand-swimmer: the sandfish lizard native to the Sahara Desert of northern Africa.

The study provides information that could help explain how evolutionary pressures have affected body shape among sand-dwelling animals. And the work could also be useful in designing search and rescue robots able to move through sand and other granular materials.

Using X-ray technology to watch each creature as it moved through a bed of sand, researchers studied the waves propagating down the bodies of both the snakes and sandfish lizards. Granular resistive force theory, which considers the thrust provided by the body waves and the drag on the animals bodies, helped model the locomotion and compare the energy efficiency of the limbless snake against that of the four-legged lizard which doesnt use its legs to swim through the sand.

We were curious about how this snake moved, and once we observed its movement, how it moved so well in the sand, said Dan Goldman, an associate professor in the School of Physics at the Georgia Institute of Technology. Our model reveals how both the snake and the sandfish move as fast as their body shapes permit while using the least amount of energy. We found that the snakes elongated shape allowed it to beat the sandfish in both speed and energy efficiency.

Information about the factors enabling the snake to move quickly and efficiently could help the designers of future robotic systems. Knowing how the snake moves could be useful, for instance, in helping robots go farther on a given amount of battery power, Goldman said.

Supported by the National Science Foundation and the Army Research Office, the research was published online December 18, 2014, in the Journal of Experimental Biology. The study is believed to be the first kinematic investigation of subsurface locomotion in the long and slender shovel-nosed snake, Chionactis occipitalis.

Measurements made by former Ph.D. student Sarah Sharpe revealed that the snake propagates traveling waves down its body, from head to tail, creating a body curvature and a number of waves along its body that enhance its movement through the sand. As a consequence of the kinematics, the snakes body travels mostly in the same tube through the sand that is created by the movement of its wedge-shaped head and body.

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Slick and Slender Snake Beats Short and Stubby Lizard in Sand Swimming