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Timothy Rowe has been carrying the head of a rare lizard around in his pocket
for months now.
Well, it’s not a real head of Lanthanotus borneensis, but a bronze replica.
Rowe, a geology professor at the University
of Texas at Austin, “printed it out” using a ThermoJet solid object
printer that rendered a digital version of the lizard head into a wax model,
which he cast in bronze. The digital version came from ta high-resolution CT
(computer tomography) scanner run by the university’s department of geology
and used by researchers from all over the world. The scanner is a high-resolution
version of a medical CAT scanner. But, because its specimens are not alive,
it can blast fossils, rocks, even pickled lizard heads with higher energy X-rays
for longer stretches. Differing densities within the specimen either absorb
or transmit the X-rays. This pattern of absorption vs. transmission creates
a digital image of the object in 2-D slices ranging from as thick as 5 millimeters
to as thin as 5 microns. Medical scanners generally create layers 1 to 2 millimeters
thick. Because it maps density differences, the CT scan is a high-resolution
look inside any specimen.
“You can see inside the head without having to chop it open,” Rowe
says.
To render the digital scan solid, the ThermoJet solid object printer accesses
an STL, or stereo lithography file created from the CT scan. It sets down wax
layers until it builds the lizard head. Like the scanner, the printer borrows
existing technology: rapid prototyping, a key tool in the manufacturing industry
for creating solid models from computer-aided design files.
The result is a 3-D replica of the lizard’s head that is three times the
size of the original. Or, Rowe could have printed a replica of the lizard’s
brain, or a cross section of its sinus cavity.
“There’s no substitute for the real deal,” Rowe says. But the
lizard is rare and the real thing hard to find and study, he adds. “Now
I know the anatomy of the head of Lanthanotus in far more detail than I know
the anatomy of the heads of the gecko lizards living in my backyard.”
The scanner is handy for seeing inside rock samples, too. Lab director Richard
Ketcham remembers scanning a diamondiferous eclogite. “It’s one of
the only examples of diamonds in their host rock,” Ketcham says. “You
can’t study it through thin sections because the diamonds stop the saw.”
The lab has everything from meteorites, salamander heads and tiny fossils in
the queue for scanning. According to Ketcham, the department gained funding
for the scanner from the work of Rowe, a paleontologist, along with anthropologist
John Kappelman and metamorphic petrologist Bill Carlson.
From the lab’s Web site, anyone can
access digital files and look inside a purple urchin, or the head of the dinosaur
Herrerasaurus ischigualastensis. And those who own a rapid prototyping machine
can, for some specimens, download an STL file and create as many replicas of,
say, the Texas horned lizard, as they like.
Kristina Bartlett
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