Print ArticleCombining 13,000-year-old bones with 21st century auto manufacturing techniques, scientists and exhibit preparators at the University of Michigan Exhibit Museum of Natural history are reconstructing a male mastodon skeleton for an exhibit that opens to the public May 21.
Meanwhile, museum visitors can peek through special viewing windows to watch preparators assemble the skeleton, which will bear 7-foot tusks. The specimen, named the Buesching mastodon for the Indiana family on whose property it was discovered in 1998, will join the museum's female mastodon skeleton, which has been on display since the 1940s.
Paleontologists rarely find complete skeletons, so they're often faced with the task of creating realistic substitutes for the missing bones. Incomplete skeletons are even more common with fossil mastodons because humans sometimes butchered the massive, elephant-like animals and hauled off whole hunks of meat, often with the bones, says U-M mastodon authority Daniel Fisher, a professor with joint appointments in the Museum of Paleontology and the departments of Geological Sciences and Ecology & Evolutionary Biology.
In the past, scientists and exhibit preparators used a variety of techniques—borrowing bones from another specimen of the same species, size and stage of development, for instance, or manually sculpting a replacement bone, based on measurements and comparisons with the rest of the skeleton.
Now, however, Fisher and his team are using 3-D digitization, modeling and rapid prototyping—technologies that are widely used in manufacturing, especially in the automobile industry—to produce full-scale replicas of the bones they lack.
"In cases where there are paired bones in the body—left and right—but we found only one, we can generate the missing bone by making a digital model of the one we have, reflecting it on the computer and then producing a physical prototype of the reflected model," Fisher said. "Compared to all of the previous approaches, digitizing and rapid prototyping are no more expensive, require much less labor and are certainly more exact, more faithful to the original."
In the first part of the process, Fisher and students in the Undergraduate Research Opportunity Program (UROP) created digital representations of each bone using a device called a 3-D digitizer, a process that took three years for the whole skeleton. Next, technicians in the UM3D lab made the replacement bones with a rapid prototyping system that converts a digital representation back into a three-dimensional, physical object, building it up layer by layer, with each layer only 0.1 millimeter (0.004 inch) thick.
Crews of UROP students and community volunteers also made molds of the bones, which took about a week for the ribs and almost a year for the skull, said biology undergraduate student Kelly Iknayan, of Gaylord, Mich., who worked on the project last year. From the molds, students and volunteers then made fiberglass casts.
"Casting the skull was a real process, too," Iknayan said. "The exhibit preparators and lab crew spent about eight hours working together on it. It was probably the hottest day of the summer, and we all had to wear face respirators. That was unforgettable."
The skeleton in the exhibit will be assembled from the fiberglass casts so that researchers can continue studying the real bones, which are on loan to the museum from the Buesching family.
When complete, the exhibit will be significant for a number of reasons, Fisher said. "To my knowledge it will be the only display in the world with an adult male and an adult female mastodon shown together." It will also recognize the American Mastodon as Michigan's state fossil, a distinction bestowed in 2002, after Washtenaw Community College professor David Thomas and students from Ann Arbor's Slauson Middle School petitioned the State Legislature.
The expanded exhibit will showcase Fisher's contributions to understanding how mastodons lived, died and became extinct some 10,000 years ago. Using evidence from tusks, bones, excavation sites and comparisons with other Ice Age animals, Fisher has made some surprising discoveries. While excavating an 11,000-year-old mastodon in southern Michigan in the late 1980s, he found the first evidence that Ice Age hunters in North America butchered mastodons and preserved the meat by storing it underwater. Other examples of butchered mastodons have since been found in Ohio, Indiana, Michigan and New York.
More recently, Fisher's studies of bone damage on fossil remains of mature mastodon males—aided by 3-D computer graphics—showed that some died of wounds inflicted by the tusks of other males during combat. The Buesching mastodon, in fact, appears to have been killed in a fight with another male mastodon and then butchered by humans.
Fisher and a team of assistants also discovered a set of 30 mastodon footprints, believed to be the longest and most complete mastodon trackway ever found, near Saline, Mich., in 1992. A 40-foot cast of the trackway is on display at the museum.
"Dan Fisher is an internationally renowned scientist, but his work is very accessible; it's not something esoteric that you need a Ph.D. to understand," said museum director Amy Harris. "The expanded exhibit offers us an opportunity to feature his research in interesting and engaging ways."
In addition to being an impressive addition to the museum's exhibit space, the Buesching mastodon is important for what it can contribute to scientific understanding, Fisher said. Whereas most mastodon specimens are only about 20 percent complete, 70 to 80 percent of the Buesching mastodon's skeleton was found.
"Having even a few specimens as complete as this one removes a lot of the guesswork that would otherwise be involved in studying a larger number of more incomplete specimens," said Fisher, who plans to continue studying the actual skeleton after the exhibit opens. "We have done some work on the tusks and teeth, to recover the kinds of information on health, reproductive history, diet and climate that are the focus of a lot of my research. Once the exhibit opening is behind us, I hope to be able to concentrate more on the interpretation of this animal's history and what it can tell us about late Pleistocene events."
Leading up to the exhibit opening, the museum is offering a semester-long series of public educational events, aimed at both adult and family audiences, exploring the theme, "Mastodons and the Ice Age." A schedule of events is available at http://www.exhibits.lsa.umich.edu/New/Events/. The public can help support the new exhibit through a "buy-a-bone" program. Information on bone sponsorships is available at http://www.exhibits.lsa.umich.edu/New/BAB/Big.html.
Source : University of Michigan
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