In the Field
How do we find dinosaurs in the Cedar Mountain Formation? Do we just start digging? No, because the chance of finding anything that way is pretty slim. Instead, we let Mother Nature do the digging for us and we just go looking for the fossils She uncovers. Mother Nature does most of Her digging with a shovel of rain, aided by the jack hammer of ice. The process, better known as erosion, is slow because precipitation in the desert is low. Where rain fall is high, such as the east coast of the US, vegetation blankets the landscape making erosion less likely to occur and hiding any fossils that might be exposed. That is why most dinosaur specimens are found in the desert.
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Erosion has excavated deeply into the Cedar Mountain Formation south of Green River, Utah. Such “badlands” are where we look for dinosaur bones. The lack of vegetation allows what little rain that falls in the desert to have a major impact on the landscape.
Most of the land where the Cedar Mountain Formation is exposed is controlled by the Bureau of Land Management or by the State of Utah. Thus, the dinosaur bones are either owned by the Federal or State government. Before we can go looking for dinosaurs, we need to get the appropriate permits. The hassle for being caught without the permits by the BLM Ranger or State Law Enforcement just isn’t worth it.
Hunting dinosaurs in the Cedar Mountain Formation requires a great deal of patience because fossils are scarce. Days can pass without so much as a fragment being found. The hunting is done on foot by walking the exposures and scanning the ground all around for fragments of bone. Bone fragments are recognizable because of color (it is usually a different color than the surrounding rock or dirt), shape (it usually has a distinct shape, rather than the irregular shape of a rock), and texture (fossil bone usually has a fibrous structure). Sometimes a rock can have the appearance of dinosaur bone requiring the tongue test. A dinosaur bone really does stick to your tongue, possibly because the saliva is pulled into the microscopic pores or openings (weird, huh?).
Fragments of dinosaur bone as found on the surface. Note their regular shape (somewhat) and generally lighter color as compared to rocks (mostly black).
Prospecting for dinosaur bones means walking a lot, while scanning the surface for fossil bone eroding out
Good places to look are bases of steep slopes where fossils that have eroded out on the slopes will accumulate, as well as gentle slopes where fossils eroding out may not be moved very far. Once bone has been found, it is traced uphill to where it might be eroding out. Sometimes it means digging around a little because soil can sometimes cover the exact spot. Having found the bone, removing it is the next step.
Dinosaur bone is rarely intact. Instead, it is usually fragmented because of weathering. Weathering is Mother Nature’s way of breaking rock up, most commonly by the expansion of ice or by the expansion caused by the sun’s heat. Broken fragments are glued together (we use superglue), and cracks sealed with a consolidant, or lacquer. Many museums use some sort of plastic resin (we use polyvinyal acetate), either as beads or liquid, that is dissolved or thinned with acetone. The acetone carries the resin into the fossil and evaporates leaving the resin behind to glue the fragments together.
Note taking is an important aspect of field work. Here, Allen Shaw is recording latitude and longitude of the site, rock type, formation, stratigraphic position within the formation, and sketch map of the bones as they lay in the ground.
Allen's sketch map of Lorrie's Site, an ankylosaur bone bed.
The next step is to make a hard shell or “jacket” around the fossil so that it can be removed in one piece. Burlap strips soaked in plaster of Paris, a technique developed in the 1880s, remains the best method. First, the rock surrounding the fossil is removed, leaving it on a pedestal of rock. Second, the fossil is slightly undercut around the edges to give the plaster a surface to hold. Third, a separator of some time needs to be placed over the bone so the plaster does not stick to the fossil.
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Bob McCarroll using plastic trash bag as a separator between plaster and fossil
Traditionally, this separator has been toilet paper, paper towels or newspapers, which have been wetted to conform to the fossil. But aluminum foil or plastic has also been used. We use sheets of plastic (trash bags) so that later in the lab, the consolidant doesn’t glue the fossil to the paper as sometimes happens. Next, burlap is cut into strips 6” or more wide and a foot or more long. These are soaked in water, rolled from one end and wrung out (these have been nick-named “burritos” by my volunteers for some reason).
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Tim Seeber wetting burlap strips and rolling them into "burittos".
Next, 1-2” of water is added to a basin and plaster of Paris is sprinkled in until the plaster has soaked up all the water.
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Sprinkle plaster of Paris until all the water is absorbed before mixing
Now it is mixed and ready for use; it should be the consistency of thin yogurt or heavy cream. The burlap strips are unrolled from one end of the basin, patted into the plaster, and very loosely rolled at the other end into a “burrito.” The burlap is then slowly unrolled the length of the fossil, starting down the middle (this will give burlap strips along the sides something to hold).
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Yuya Ishida and Kentaro Chiba encasing a fossil with burlap and plaster
If the fossil is large and heavy, then several layers of burlap and plaster are applied. Sometimes a board may be used to reinforce the burlap to keep the fossil from flexing. Once the plaster begins to set, the surface is smoothed because rough, dry plaster can be painful to handle.
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Smoothing the plaster jacket (note the "toe" tag)
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A plaster jack that has been flipped over and excess rock removed. It is now ready to be capped with burlap and plaster.
Life in Camp
Life in the field has its own pace. I usually have two types of camps depending on what we are doing. A permanent camp is set up near where we are planning to work for a long time. Many of my volunteers bring or rent trailers, while others of us either sleep under the stars or in tents.
Permanent camp near Lorrie's Site.
Roving or prospecting camp somewhere near Cisco, Utah.
The other, roving camp tends to move as we prospect. Owing to the terrain we cross, trailers are not an option, so we either sleep in tents, under the stars, or in the vehicles.
Regardless of the style of camp, I usually do the cooking since I’ve been a cook in various restaurants (some of my field recipes are available here). But everyone is expected to pitch in with dishwashing or making salads.
Pitching in to do the dishes (permanent camp uses a cook tent).
Pitching in to make the salad (roving camp using a corral).
Breakast near Lorrie's Site (permanent camp). Hot coffee and a cold breakfast is a great way to start the day.
Lunch during a prospecting trip. The only shade was the vehicle.
Dinner at a permanent camp south of Green River.
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Enjoying a sunset in the desert.
Quite time in the evening.
About an hour later, the jacket is undercut and rolled over.
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Flipping the plaster jack over
Excess weight is reduced by removing the capping rock down to the fossil layer (the fossil, however is not cleaned of rock completely at this point). Consolidant is applied to any fossil exposed, then a cap of plaster and burlap applied over pieces of plastic separator covering the bone.
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"Capping" the plaster jacket
The plaster jack is ready for an identification number or “toe” tag (a identification tag on a string) with the information written on it. The jacket is now ready for transport back to the lab.
