If the cavity reveals the form and markings of the inner surfaces of the organism, it is termed an internal mold or steinkern. Many times an external mold is later filled with mineral matter and forms a cast. It is sometimes difficult to distinguish between an internal mold and a cast, but on the surface of a cast the external part of the original animal is represented while on the surface of an internal mold the internal surface of the shell is represented. Impressions made by jellyfish and other delicate organisms are also found in some fine-grained sediments. Round holes in clam and other shells indicate that predator snails once sought the soft part of the animal as food.
Coprolites are fossilized animal excrement.
They are important because they may show the structure of the animal's gut as well as indicate its diet. Trilobite from Paleozoic rocks. A person who studies fossils is called a paleontologist. It is through paleontology that geological evidence of past life and the biological evidence of present day organisms are integrated. Return to Index of DMG Notes and Teacher Features Copyright California Department of Conservation, Division of Mines and Geology, 1997.