ANIMALS MAKE CORKSCREW BURROWS
the last quarter of a billion years or so, a variety of vertebrate animals
have excavated deep, spiral-shaped burrows into the ground. Some of
them went several feet straight down in a helix.
paleontologists called them devils corkscrews and
spent many years speculating on the origin and purpose of these mysterious
structures. The earliest reports are from the 1890s.
happens with new scientific discoveries, these odd constructions that
had no modern counterpart prompted various explanations as to their
origin and purpose. Among the proposals: They were the tunnels of giant
sponges; they were passageways left by some form of vine; they were
animal burrows. Almost a century after their discovery, spiral burrows
in Nebraska were confirmed to have been made by an extinct beaver.
animals living today, including ants, mice and prairie dogs burrow into
the ground. Almost every turtle in the world digs a nest in sand or
dirt to lay its eggs. According to Bob Zappalorti, who has studied pine
snakes living in sandy habitats in New Jersey, these big snakes dig
horizontal tunnels more than 6 feet long and a foot deep to make a chamber
for laying their eggs.
tortoises of the Southeast are noted for their underground burrows,
to which they retire at night and during cold weather, that often extend
more than 20 feet horizontally. But the true purpose of the enigmatic
corkscrew tunnels of long ago kept scientists bewildered for decades
after their discovery, in part because no living equivalent existed
for investigation. But thanks to Sean Doody of Southeastern Louisiana
University and his studies of a giant Australian lizard, scientists
now know what kind of animal would dig a spiral staircase beneath the
studied the ecology and behavior of yellow-spotted monitors in Western
Australia. These enormous lizards, which are related to Komodo dragons,
reach lengths of more than 5 feet. I remember seeing one in northern
Australia standing on its back legs and supported tripod-like by its
tail as it looked around at the customers in a restaurant with outdoor
seating. I decided to eat inside.
showed me photographs of what looked like an archeological dig in desert
habitat. He and his colleagues were using shovels to carefully excavate
a large area, several yards on each side and above their heads to investigate
the nesting habits of the big lizards.
his crew were rewarded for their meticulous quarrying efforts by discovering
corkscrew-shaped tunnels going straight down below the desert floor.
At the bottom, they found a nesting chamber. They excavated and measured
52 of these spiral tunnels, which were capped at the top, preventing
the entry of would-be predators. According to their scientific paper
in the Journal of the Linnean Society, they are the deepest
known of any vertebrate, and by far the deepest of any reptile.
The deepest ones went straight down for more than 11 feet, like spiral
steps in a lighthouse.
team concluded that egg survival is the explanation for the unusual
architecture. The lizards nest in a region and season of near perpetual
drought, with egg incubation taking 8 months. Desiccation is a continual
threat to eggs in such an environment, and a deep nest chamber solves
that problem. Also, upon hatching, the young lizards can make their
way to the surface without being buried alive or expending energy digging
concluded that the mystery of the ancient corkscrews discovered more
than a century ago has been solved. Devils corkscrews were
used mainly for nesting or rearing young, because helical burrows of
extant vertebrates are generally associated with a nest.
the time and effort needed for an animal to dig a long spiraling tunnel
deep into the ground. Another of Mother Natures wonders. Imagine,
too, the training, skill and dedication of scientists like Sean Doody
and colleagues who help solve the mysteries of the natural world.
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