Scientists study dinosaurs by examining fossils, which are animal remains that have turned to stone. If a dinosaur died near a river or in a swamp, it stood an excellent chance of being preserved. Its body might sink into the mud, or floodwaters might float it downstream, where it would end up on a sandbar, on the bottom of a lake, or even in the sea. After the flesh decayed, the bones would be covered by sediments, such as mud or sand. The weight of accumulated layers of sediment would compress the remains and turn them into rock: mud into shale, sand into sandstone, limey oozes into limestone or chalk.
The way a fossil is studied is determined by the category to which it belongs. The first category is petrified fossils. They may be preserved in two ways. In replacement, minerals replace the original substance of the animal after water has dissolved the soft body parts. In permineralization, minerals fill in the small air spaces in bones or shells, thereby preserving the original bone or shell. The second group of fossils is composed of natural molds that form when the bodies dissolve. Scientists make artificial casts of these molds by filling them with wax, plastic, or plaster. The third type is prints, which are molds of thin objects, such as feathers or tracks. Sometimes, even skin is preserved. Prints are formed when the soft mud in which they are made turns to stone. Scientists can determine the length and weight of the dinosaur that made a set of footprints by studying the depth, size, and distance between them.
Most fossils are found in sedimentary rocks, which lie beneath three-fourths of the earth. The best collecting areas are places where the soil has worn away from the rocks. Areas in Colorado, Montana, Wyoming, and Alberta, Canada, have been especially rich in fossils. Most of the finds consist of no more than scraps of limb bones, odd vertebrae, loose teeth, or weathered lumps of rock with broken bone showing on the surface. Once a
Image Not Available scientist has discovered a few fossilized fragments, he or she combs the area to find the rest of the animal. If the skeleton is embedded, it is extracted with the help of a wide variety of tools, ranging from picks and shovels to pneumatic drills. Loose fragments are glued back into place, and parts that are too soft or breakable are hardened by means of a special resin solution that is sprayed or painted on.
As the fossil is uncovered, it is encased in a block of plaster of paris. (A more modern method uses polyurethane foam instead of plaster.) After the entire surface is covered, the fossil is rolled over, and another layer of plaster is added. After the fossil has been transported to the museum, the plaster is removed. The "development" stage involves the removal of the rock around the bones. The oldest way is by hand, using tools such as hammers and chisels; a more modern technique uses electrically powered drills similar to dentists' drills. Sandblasting and chemicals may also be employed. After the fossil is cleaned, it is ready for mounting. The bones are fastened to a steel framework that makes the skeleton appear to stand by itself.
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