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FIGURE 4.9 (opposite) Steps in excavation of a vertebrate fossil, in this case a partially exposed skull and other bones of a metoposaur, a large amphibian that lived at the same time (and in this case, the same region) as early dinosaurs, Chinle Formation (Late Triassic), Arizona. (A) After cleaning the area, workers estimated the extent of the fossil and dug around the defined area. (B) Digging of the rock underneath the fossil established a pedestal. (C) One worker placed wet paper towels on the top to cushion and separate the fossil from the plaster. (D) Another worker placed the plaster-soaked burlap strips for the jacket all around the pedestal. The workers then waited until the next day for the plaster to have hardened before breaking the pedestal, turning over the rock, and jacketing the underside.

Dinosaur Jacket Plaster Pedestal

FIGURE 4.10 Pelvis of Apatosaurus from the Morrison Formation (Late Jurassic), western Colorado, still partially encased in its protective jacket and in a preparatory lab associated with the former Museum of Western Colorado, Grand Junction, Colorado. Notice the plastic model sauropod in the background, ready to help with estimating the weight of the original animal (Chapter 1).

FIGURE 4.10 Pelvis of Apatosaurus from the Morrison Formation (Late Jurassic), western Colorado, still partially encased in its protective jacket and in a preparatory lab associated with the former Museum of Western Colorado, Grand Junction, Colorado. Notice the plastic model sauropod in the background, ready to help with estimating the weight of the original animal (Chapter 1).

prefer the plaster of Paris method, which has been in use for more than 100 years (Chapter 3).

The specimen is left while the plaster hardens completely. Only then is the support under the pedestal broken so that the fossil can be turned over carefully to apply the remainder of the jacket. For later cataloguing, important information about the fossil, such as the date collected, preliminary identification, specimen number, orientation (indicated by a north arrow), and location, are written on the jacket. This also keeps the fossil from being mixed up with other, similar-looking, jacketed specimens. The snug and safe fossil is now ready for transport out of the field area, carried by people on foot (if the specimen is small enough), in land-based vehicles, or in extreme cases by helicopter.

In a preparatory laboratory, a jacketed specimen is cut open and the excavation begins anew, with the goal of liberating the fossil from its surrounding rock (Fig. 4.10). A preparator will use human energy and a variety of tools to separate the fossil from its entombing sediments. Just as in the field, the amount of time taken to extract bones from rock depends on the cementation of the rock and fragility of the fossil. Skeletal material is also commonly fragmented, requiring the prepara-tor to handle each small piece with care so that paleontologists can re-assemble the pieces accurately later. Preparators are among the most patient and skilled people in paleontology, some operating with the precision of surgeons.

Once the dinosaur bones are prepared, they can be placed in dynamic public displays, baring their teeth or bearing their young. However, most skeletal remains of dinosaurs return to dark quarters, tucked away in storage drawers or shelves for future research. Because of its great weight, real bone is rarely mounted in a museum; supporting these hard-earned but heavy specimens and keeping them from being damaged or vandalized is an expensive technical problem. Instead, casts are made from the original bones using artificial materials, such as fiberglass. These strong,

FIGURE 4.11 Tyrannosaurus rex mount, which uses artificial casts of the bones and thus allows for the unusual pose of the display; Denver Museum of Science and Nature, Colorado. Author (imitating the pose in the foreground) for scale.

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