Those fossils slated for removal from the rock are slowly and carefully excavated using techniques designed to prevent or minimize damage to the specimen.
Such fossils often become part of museum or university collections.
A shell or bone that is buried quickly after deposition may retain these organic tissues, though they become petrified (converted to a stony substance) over time.
Unaltered hard parts, such as the shells of clams or brachiopods, are relatively common in sedimentary rocks, some of great age.
The hard parts of organisms that become buried in sediment may be subject to a variety of other changes during their conversion to solid rock, however.
Solutions may fill the interstices, or pores, of the shell or bone with calcium carbonate or other mineral salts and thus fossilize the remains, in a process known as permineralization.
Often such specimens are not carefully documented or excavated, resulting in a loss of data from the site and risking potential damage to the specimen.Most major groups of invertebrate animals have a calcareous skeleton or shell (e.g., corals, mollusks, brachiopods, bryozoans).Other forms have shells of calcium phosphate (which also occurs in the bones of vertebrates), or silicon dioxide.By contrast, the soft parts of animals or plants are very rarely preserved.The embedding of insects in amber (a process called resin fossilization) and the preservation of the carcasses of Pleistocene mammoths in ice are rare but striking examples of the fossil preservation of soft tissues.The study of the fossil record has provided important information for at least four different purposes.The progressive changes observed within an animal group are used to describe the evolution of that group.Leaves, stems, and other vegetable matter may be preserved through the process of carbonization, where such parts are flattened between two layers of rock.The chemical reduction of the part produces a carbon film that occurs on one layer of rock, while an impression of that part occurs on the other layer of the rock.Fossils of hard and soft parts that are too small to be observed by the naked eye are called microfossils.Some fossils are completely devoid of plant and animal parts but show evidence of an organism’s activities.