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A lizard that can
swim on dry land
By Daniel Strain
The sandfish lizard wriggles through
desert sands like a sci-fi monster. Now,
using computer simulations and bendy
robots, researchers at Georgia Tech in
Atlanta and Northwestern University in
Evanston, Ill., have taken the most complete look yet at the physics of burrowing
animals. And, boy, does this reptile wriggle,
the team reports online March 4 in the
Journal of the Royal Society Interface.
“This particular behavior is built for
speed,” says study coauthor Daniel
Goldman, a physicist at Georgia Tech.
Like the deadly sandworms in the
Dune science fiction series, a host of animals from scorpions to snakes burrow in
desert sands across the planet. It’s not
easy to study how these creatures careen
through their environments, Goldman
says. Scientists have a good idea how
water behaves in the wake of an undulating eel or how air flows over a bird
wing. But shuffling sand grains ping off
each other like billiard balls in a wickedly
complicated game of pool.
X-ray studies have shown that sand-
fish lizards (Scincus scincus) navigate
such chaos with a wormlike wriggle,
Goldman says, tucking in their legs and
curling from side to side in S-shaped
waves. The creatures can grow to
4 inches long, and a fast sandfish lizard
dive covers two body lengths per second.
But just how the lizards achieve such
speed in a complex sandy environment
wasn’t clear. For that, Goldman’s team
turned to a new set of tools.
Computer simulations of lizards negotiating a sea of small glass beads can
reveal how single grains respond when
a real sandfish swims through sand.
Search and Rescue at Texas A&M University in College Station. She designs
robots to help in the aftermath of disasters like earthquakes or mudslides.
When it comes to machines that can dig
like earthworms and slip through rubble,
nothing like that exists. “There’s a lack
of any technology short of a shovel,” she
says. Burrowing animals could inspire
new machines, but so far few studies
have been able to capture the constraints
robots would face in dirt-filled or muddy
environments. “This is the first I’ve seen
that I said, ‘OK, we’ve got it,’ ” she says.
Robots inspired by animals are neat,
says Eric Tytell, a researcher at Johns
Hopkins University who studies how
fish swim in water. But the Georgia team
flipped that inspiration around, too.
Goldman and his colleagues used robots
to get a better grasp of biology. And that’s
really clever, Tytell says.
Rise of the creepy crawler
Fossils of an ancient “walking cactus” suggest how ancestors
of today’s lobsters, insects, spiders and related groups went
from squishy to spiky. Dating back about 520 million years, the
thumb-sized creature probably scuttled along shallow seafloors,
says Jianni liu of Northwest university in Xi’an, china, and the
Free university of Berlin. in the Feb. 24 Nature, she and her
colleagues christen the species Diania cactiformis. Discovered
in southwestern china, the animal’s jointed legs appear to have
had a hard covering of armor. an armored outer skeleton and
jointed legs are today defining features of arthropods, including
crustaceans, insects, spiders and mites. — Susan Milius
From top: YaNg DiNg; J. liu