WASHINGTON - Scientists have found that sandfish place their limbs against their sides and create a wave motion with their bodies to propel themselves through granular media, just like a snake.
Researchers from the Georgia Institute of Technology conducted this first thorough examination of subsurface sandfish locomotion.
“When started above the surface, the animals dive into the sand within a half second. Once below the surface, they no longer use their limbs for propulsion - instead, they move forward by propagating a traveling wave down their bodies like a snake,” said study leader Daniel Goldman, an assistant professor in Georgia Tech’s School of Physics.
The research team used high-speed x-ray imaging to visualize sandfish burrowing into and through sand, and used that information to develop a physics model of the lizard’s locomotion.
The sandfish used in this study inhabits the Sahara desert in Africa and is approximately four inches long. It uses its long, wedge-shaped snout and countersunk lower jaw to rapidly bury into and swim within sand.
To conduct controlled experiments with the sandfish, the researchers built a seven-inch by eight-inch by four-inch-deep glass bead-filled container with tiny holes in the bottom through which air could be blown.
The air pulses elevated the beads and caused them to settle into a loosely packed solid state.
Repeated pulses of air compacted the material, allowing the researchers to closely control the density of the material.
Since a sandfish might encounter and need to move through different densities of sand in the desert, the researchers tested whether sandfish locomotion changed when burrowing through media with volume fractions of 58 and 62 percent.
“Since loosely packed media is easier to push through and closely packed is harder to push through, we thought there should be some difference in the sandfish’s locomotion,” said Goldman.
“But the results surprised us because the density of the granular media did not affect how the sandfish traveled through the sand; it was always the same undulatory wavelike pattern,” he added.
For a given wave frequency, the swimming speed depended only on the frequency of the wave and not on the density.
Unexpectedly though, the animals could swim a bit faster in closely packed material by using a higher frequency range.
The scientists found that the faster the sandfish propagate the wave, the faster they move forward through granular media - up to speeds of six inches per second.
This speed allows the animal to escape predators, the heat of the desert surface and quickly swim to ambush surface prey they detect from vibrations. (ANI)