Fossil and Fossilization

A fossil identified in the field is not immediately chiseled out of its matrix. First, photographs are taken to show the relationship of the fossil fragments, and the investigator notes the rock type and age, and the fossil's orientation. Then a block of rock matrix that contains the entire fossil is cut out with a rock saw, wrapped in muslin, and wrapped again in wet plaster, a process known as jacketing. The jacketed fossils may additionally be stored in protective crates for air transport.

In the laboratory, the external wrappings are removed, exposing the fossil in its matrix. The technique used to remove the excess rock varies with the type of rock and type of fossil, but three methods are common. Needle-sharp pointed tools, such as dental drills and engraving tools, may be used under a binocular microscope; or pinpoint blasting may be done with a fine abrasive powder; or acid may be used to dissolve the rock. Because some fossils also dissolve in some acids, the fossil's composition must be determined before a chemical solvent is used. If the investigator wishes to see the complete anatomy of the fossil, the entire rocky matrix may be removed. Thin slices of the fossil may be obtained for microscopic study. If replicas are desired, the fossil may be coated with a fixative and a rubber cast made. For security purposes, most prehistoric skeletons on display in museums and public institutions are models cast from a mold, and not the original fossil itself.

The study of fossils is not limited to freeing the fossil from its matrix, looking at it microscopically, or making articulated reproductions to display in museum halls. Since about 1980, a variety of techniques developed in other fields have been used to make discoveries about the original life forms that were transformed into fossils. Immunological techniques have been used to identify proteins in fossilized dinosaur bones. The ability to recover DNA, not only from insects preserved in amber but also from fossilized fish and dinosaurs, may soon be realized. Studies of temperature-dependent oxygen isotopes formed during fossilization have been used to support the theory that dinosaurs were warm-blooded. And even as laboratory research is moving toward the molecular biology of fossilized organisms, aerial reconnaissance techniques for identifying likely locales of fossil beds are being refined. The true value of a fossil, however, is realized only when its relationships to other organisms, living and extinct, and to its environment are known.