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Worn to the Bone

Thanks to several Hollywood blockbusters, we are familiar with the image of paleontologists digging in the field, but what happens after the big discovery when the end credits roll? What occurs between the field and museum in the life of a prehistoric bone?

According to Mr. Kyle Davies, Museum Preparator for the vertebrate paleontology department, once a fossil is discovered in the field, paleontologists dig a trench around it and surrounding rock. They then cover the piece with thin tissue paper, which serves as a protective barrier, before coating the artifact in a mixture of plaster and burlap. Once the plaster has set up, they undermine the specimen, cautiously remove it from the ground and wrap the exposed side in plaster and burlap. Paleontologists refer to this completed object as a field jacket.

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An unopened field jacket.

Field jackets, like the one above, are then sent to museums for further preparation. The above field jacket contains Tenontosaurus bone from a dig at the McLeod Correctional Facility near Atoka, Oklahoma on May 2, 2002. The Tenontosaurus, a fairly common herbivore from the Cretaceous Period, roamed much of North America approximately 110 million years ago. This particular field jacket remains unopened, but will be examined by the 2013 Paleo Expedition ExplorOlogy team this summer.

When ready for preparation, the field jacket is opened using a cast-cutter, the same tool used by medical doctors. Then, paleontologists begin the tedious process of slowly chipping away at unwanted rock to expose the bone.

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A typical tool-kit

Due the extreme level of caution required, removing bone from a field jacket may take several thousand hours. In the case of the Sam Noble Museum’s Pentaceratops skull, the largest found in the world, the removal process required roughly 3,000 hours. For this reason, the vertebrate paleontology department utilizes a large number of trained volunteers

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A pin vise chips away at unwanted rock.

Of course, common practices have evolved over many years to determine the most efficient means of specimen removal.

“Everything we do is done under the lessons from the past about what does and doesn’t work,” explained Mr. Davies.

Once enough bone becomes visible, paleontologists seek to identify the species. But how do scientists identify an entire dinosaur from simply bone?

“How do you know what model car you have?” asked Mr. Davies in reply. “You know by looking at it. An expert could tell you a model and make just by looking at a tail light.” He explained that in this way, identification of species relies heavily on specialized knowledge and previous training in comparative anatomy.

Occasionally bone fragments require repair, which calls for specialized forms of adhesive glues. Once the pieces are glued together, paleontologists use the help of a sandbox and gravity to hold the bone together as it dries over several minutes to hours. In the video below, Mr. Davies explains this process.

From here, paleontologists prepare the bone for study, display or storage. For display, bones are reconstructed before use. Sometimes, but not always, they are replaced with precision castings made by molding and casting the actual bones or reconstructions in the lab. Staff members in either vertebrate paleontology or exhibit departments then paint the castings to resemble the actual bone. Finally, staff workers assemble the bones to form full skeletons inside the one of the museum’s exhibit dioramas. Museums are most likely to showcase dinosaurs for which they possess many of the actual skeletal pieces, such as the Sam Noble Museum’s Tenontosaurus.

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Our Tenontosaurus display

The original bones rest inside the highly organized walls of a massive collection facility. Here they are protected and available for scientific study, or further replication.