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University of Wyoming

MUSEUM OF THE ROCKIES SCIENTISTS PRESERVE
"BIG AL" FOSSIL

(NOTE: This is the second in a series of articles about "Big Al," an Allosaurus that roamed Wyoming 145 million years ago. The first display skeletal cast of "Big Al" is on exhibit at the University of Wyoming Geological Museum.)

Jan. 29, 1996 -- While the only skeletal display of "Big Al" is at the University of Wyoming Geological Museum, the work of preserving the 145 million-year-old Allosaurus fossil was done at the Museum of the Rockies (MOR) at Montana State University (MSU) in Bozeman.

"The decision by the Bureau of Land Management to preserve and display the fossil in the West and the cooperative effort with the Museum of the Rockies provided a great opportunity for Wyoming," says Brent Breithaupt, UW Geological Museum director. "The UW Geological Museum did not have the resources or the personnel necessary to perform the kind of work that is done at the Museum of the Rockies. The original fossil is close enough to UW for students and faculty to study and UW has the only full cast on display for educational purposes."

With the development of new plastics in recent years, using casts instead of the actual fossils is a popular way for museums to create dinosaur displays. The casts are much lighter and easier to manipulate, creating much more interesting and life-like poses.

"Most important, though, is that by using a cast instead of the original fossil, scientists can continue to study specimens while the public enjoys the display," Breithaupt says. "Previous mounting techniques sometimes damaged the specimens, and it is difficult to continue research once fossils are damaged. Research on 'Big Al' is providing new, exciting information about the life and times of this prehistoric Wyoming beast."

"Big Al" was discovered in the summer of 1991 on BLM land near Shell, Wyo. Fossil preparation and display molds were completed in December 1995.

"People work all their lives, and never get a chance to work on something as beautiful as 'Big Al,'" says Robert Harmon, MOR chief preparator of paleontology. "Most preparators would give their eyeteeth to work on something like this."

The Allosaurus was found in a death pose, with its neck and torso twisted due to contraction of tendons and flesh drying in the sun. "Big Al's" death in a river bed led to its rapid envelopment by sand and mud. During millions of years, the dinosaur's bones were replaced by minerals that preserved the fossil.

The fossil was moved to the MOR after it was encased in protective plaster and burlap wrappings in the field. Staff members directed by Harmon carefully removed the wrappings and separated the fossil from the rock. Delicate cleaning tools including brushes, files and compressed air devices were used to uncover fossil bones. Preservatives were applied to the fossil surface and the cracks were filled to increase its strength.

There are several steps in making a polyurethane cast of a preserved fossil. Each bone is encircled in clay, leaving a pour spout for casting. A silicone molding compound is then applied, followed by the construction of a plaster over-mold that keeps the flexible molding compound in place. The completed mold is taken apart and the specimen is removed, leaving a cavity with an impression of the entire specimen. The mold is prepared and cleaned, and the polyurethane is poured into it. After it hardens, the mold is carefully removed from the plastic cast.

Each piece of the fossil cast is checked to insure proper fitting. Holes are drilled in each of the pieces in which connecting rods are placed. The dinosaur is then reconstructed. "Big Al" is articulated to represent the dinosaur standing on its two powerful legs, with its whip-like tail elevated behind it; its threatening, talon-tipped claws extend from the hands; and its head, with its knife-like teeth, leans forward in a predatory position.

After the cast was assembled, Breithaupt went to Bozeman to oversee the disassembly, packing and transportation of the specimen to Laramie. Harmon worked with Breithaupt at UW to reassemble the specimen and put the final touches on the new display.

THE STORY OF "'BIG AL' 

On Display at the UW Geological Museum

BBC Dinosaur page featuring Big Al