- Photonics Salvages a Cretaceous Treasure:Triceratops
Daniel C. McCarthy
After some 65 million years buried in sediment and nearly 100 years more on display at the Smithsonian Institution's National Museum of Natural History, the collection of bones comprising the triceratops exhibit is ready for semiretirement. The new mount, scheduled to open this spring, will be nearly identical to the old, except it will be more scientifically accurate and more durable, with the help of photonics.
Many of the physical alterations were achieved using a virtual model that was created through optical scanning done by Scansite. The company formed a three-dimensional computer model of the original, bone by bone, using several scanners, including two halogen-based instruments from Steinbichler Optotechnik GmbH in Neubeuern, Germany. They created a template of the original mount and 3-D computer models of the largest bones, while smaller bones requiring finer detail were digitized with a HeNe laser scanner made by Cyberware of Monterey, Calif.
The first 65 million years were easy. However, after only 99 years on display at the Smithsonian Institution, triceratops is ready for controlled storage. Laser scanning and stereolithography techniques not only replicated the old bones, but also improved the overall mount's anatomical accuracy. Courtesy of the Smithsonian Institution.
When the entire dinosaur was digitized, it comprised about 6 Gb of data, according to Lisa Federici, president of Scansite. Because the head and the left humerus of the original mount had belonged to smaller animals, data editors manipulated the digitized version to improve its overall integrity.
"The head was on there only because it was the prettiest one available at the time," explained Ralph Chapman, a paleontologist at the museum. "We wanted to increase it linearly by 15 percent." The left humerus, the bone articulating with the shoulder, was enlarged by replicating a digitally mirrored version of the right humerus.
Besides improving triceratops' anatomy, optical scanning helped to better the scientists' ability to estimate the animal's most functional forelimb structure. Consequently, the angle of the legs in the new mount will be slightly more vertical than the one created in 1905. "We learned, for instance, that the front legs could lock while sleeping or when in battle," Chapman said. "It's logical that they would be that way from how the bones articulate. I think this is the closest we'll get to an accurate representation without a time machine."
An SLA 7000 stereolithography machine manufactured by 3D Systems converted digital data constructed from original or digitally prototyped bones to form solid models from polymer. In this process, digital data are broken down into thin slices, which form a map that directs a frequency-tripled Nd:YVO4 laser produced by Spectra-Physics in Mountain View, Calif., to paint each slice on a platform submerged in resin. Once the ultraviolet beam hardens the resin into a layer, the platform drops and the next layer is produced. A plaster poured into molds formed from the prototypes created the final casts for mounting.
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