A species of skink (Scincus scincus), the sandfish moves as quickly through sand as a fish moves through water. It grows to about six inches (fifteen centimeters) long and lives in the hot deserts of North Africa and the Middle East. It is also kept as a pet in sand-filled containers, although it spends most of its life under sand.
“This desert animal has a thing or two to teach materials-handling and process-technology specialists,” researchers said last week after using an MRI scanner to study how efficiently the sandfish swims through sand.
The scientists hope to apply the insights they gained to improve technologies for the handling of granular materials. “Whether it’s gravel, sand, or flour, optimizing the technology for handling such materials could significantly reduce energy and maintenance costs for businesses such as quarries and industrial bakeries in the future,” said Werner Baumgartner, a professor in the department of Cellular Neurobionics at RWTH Aachen University in Germany.
In an article published in the journal PLoS ONE, Baumgartner and colleagues described what they found when they used an MRI scanner to observe the sandfish swimming through sand.
“We took a round container that would fit snugly into the MRI and filled it with sand,” Baumgartner said. The method provided a visual record of the animal’s movements in the sand as viewed from above and from the side.
It had been thought that to move efficiently through sand the sandfish pulled its legs in against its body. But the experiments revealed that it moves its legs back and forth in a fixed pattern. “This seems illogical at first, because sand provides resistance,” says Baumgartner. “But we found out that its leg movements are very well coordinated with the wriggling of its body.”
It turns out that the sandfish moves in a way very similar to the crawl stroke in swimming. When the animal moves its head or upper body to the left, for example, it leaves a gap and thus an area of looser, less dense sand to its right that allows the animal to move its front right leg forward with little effort.
Conversely, when the sandfish moves its upper body to the right a moment later, the sand on that side is compressed. This compact sand provides a stable basis from which to push off its front right leg.
“The time displaced-movements of the lizard’s legs according to this principle add up to a very efficient and extremely rapid form of locomotion,” Baumgartner said.
The biologists also discovered that the sandfish always moves through sand at the same frequency. “The lizard’s winding movements produce vibrations in the sand,” Baumgartner explained.”Our experiments showed that these vibrations have a consistent frequency of 3 hertz (three motions per second).”
The scientists hypothesized that this frequency allows the animal to move forward with the least amount of energy, and subsequent tests confirmed their assumption.
They did so by building an aluminum model of a sandfish with a motor and having it move back and forth through the sand at different frequencies. They found that the force required to move the aluminium sandfish forward was lowest at exactly 3 Hz, as that was when the sand surrounding its body was loosest.
“The sandfish adapted to moving efficiently through granular material over millions of years,” Baumgartner said. “Scientists are increasingly applying insights gained from nature to a wide range of innovative technological uses. For example, we can use mathematical and computer-based models to calculate the ideal frequency for transporting all different kinds of granular materials.”
(A) A living adult sandfish in the hand of the experimenter. (B) top-view (C) side-view of a 3D-reconstruction of a fixed sandfish. The spatula-shaped snout, the streamlined body shape, the smooth integument, long limbs as well as long and fringed digits can be seen representing typical adaptations to live in lose sand, scientists noted.
All images on this entry from research article published in Plos ONE: Baumgartner W, Fidler F, Weth A, Habbecke M, Jakob P, et al. 2008 Investigating the Locomotion of the Sandfish in Desert Sand Using NMR-Imaging. PLoS ONE 3(10): e3309 doi:10.1371/journal.pone.0003309