Ralph Chapman is a paleontologist by training. He runs the Applied Morphometrics Laboratory at the Smithsonian's National Museum of Natural History. Ralph began by presenting a cladogram which described the evolution of animal families that lead to Triceratops. He then discussed the history of the Triceratops specimen beginning with its initial discovery and mounting. He ended his presentation with a thorough description of the repositioning of the skeleton, which had been a controversial topic of discussion between paleontologists for the past 25 years.
The refurbished Triceratops skeleton
A Little Background
The history of this skeleton begins in 1888 when Othniel Charles Marsh, Vertebrate Paleontologist for the U.S. Geological Survey and Professor, Yale University, learned that John B. Hatcher, one of his field collectors, had been shown bones of a horned dinosaur at Lance Creek, Niobrara (now Converse) County, Wyoming. Marsh ordered Hatcher to immediately start collecting these skeletons. From 1889-1892 Hatcher collected at least 50 individuals of horned dinosaurs, more than 30 of which included skulls. Most of these were Triceratops. Prior to Hatcher's collection, Triceratops was known only from horn cores. In fact, Marsh himself described a pair of these horns as a new species of bison only one year earlier, in 1887.
Dr. Marsh died before he could complete his book on the horned dinosaurs. The collection had been built with both private and government money; so it was split up and a portion came to the Natural History Museum in Washington. The museum's Triceratops became the first mounted horned dinosaur. With the assistance of Norman H. Boss, preparator, Charles W. Gilmore, future curator of fossil reptiles, mounted the Triceratops skeleton from 1903 - 1905. An attempt was for the 1901 Colombian Exposition, but the photo suggests that a poor mock-up of wood and some plaster casts was most likely the result.
Since none of the specimens collected by Hatcher were complete, Gilmore and Boss used bones from several individuals of similar size to make this first mount. Between 10 and 13 different specimens were used to complete the work! This lead to some poor symmetry matches, and improper relative sizes. The new restoration team estimated the skull on the original mount was 15% too small for the body. Other parts of the Triceratops were missing completely. None of the back foot bones of any Triceratops were ever found in articulated form until recently. In 1903, Gilmore needed feet for the Triceratops, but no one knew what they looked like. In consultation with Hatcher, he chose feet of the proper size for a dinosaur like Triceratops from Hatcher's specimens, but those he chose turned out to be from a duck-billed dinosaur.
In the mid 1990's conservator Kathy Hawks discovered that the mounted skeleton of Triceratops was falling apart. Of all the fossils on display at NMNH, Triceratops was in the worst condition and in danger of collapse. She recommended that the brittle bones be dismantled, glued, hardened, and remounted in a padded armature. Ralph saw his opportunity and he took it. He proposed creating a virtual replica of the skeleton to the Department of Paleobiology. This digital model could be used to correct the sizing and symmetry errors. He thought this would be possible using new techniques that had recently begun to make their way out of the laboratory and into the marketplace.
The project quickly was adopted as a joint effort between Ralph's lab, the Paleobiology Department, and the Office of Exhibits, which played a great part - thanks to Linda Deck- and footed most of the bill, along with the in-kind donations of about 3/4 million dollars from companies brought in through Ralph's contacts. Paleobiology - especially through Steve Jabo - was a very important part of the virtual part of the project - as was Linda and Ralph's intern Rebecca Snyder, who did much of the work along with Art Anderson (a digitizing industry consultant and dinosaur enthusiast) and other outside people.
 Linda Deck displays the test model (above) made from a commecial model. A selection of modeling materials used for making replicas (left), wood composites, plastics, foam, and plaster. The commercial model of Triceratops and its "egg" container are also displayed. |
The decision was made to create a basic set of reference landmark points in 3D from the mounted skeleton and then scan the individual bones as they were dismounted . The laser device could be mounted in different positions around the specimen, and the resulting multiple scans stitched together to form a single mesh of data points for each bone. The hardest part was the skull. With each separate scanned bit of mesh on the final computer model colorize, the skull looks like a rainbow quilt. 20 million data points were collected on the skull through the multiple scans. These were reduced to about half a million points of non-redundant data. The limitations of the computers employed at the time prevented the practical use of larger data sets, so the final virtual model of the head contains about 100,000 points. The head was enlarged by 15% and other portions of the dinosaur that were ill-sized were replaced by mirroring the virtual bones.
Once the virtual model was complete, a desk top 1/6th scale model was manufactured using the stereolithography process (far right); and the science team gathered in a room for a day and argued to consensus a new posture for the skeleton. The major change was a more erect forelimb posture, but not elephant-like.Then the model files (SST format) of the pieces to be replaced were sent out for production. Most of the replacement bones were
milled on high precision machines. They could be made of a wide range of materials such as foam, plastics, and compressed particle wood. The skull was so huge the decision was made to use the stereolithography process, which has a limited size, but the 35 pieces generated could easily be stuck together and cured with UV light. The resulting full sized model (left) was remarkably light weight because the laser was guided to fill all the enclosed space with a honeycomb texture, not a solid fill. The full size objects were then used to make molds, from which plaster bones were created for the final mounting.The new Triceratops mount was unveiled to the public in May 2001, along with new exhibit panels and redesigned exhibit space. For more information on the restoration project, visit http://www.mnh.si.edu/highlight/triceratops/