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For this reason, one term covers the two modes of preservation: adpression.
Because of their antiquity, an unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, including blood vessels, and the isolation of proteins and evidence for DNA fragments.
Often, however, the phytoleim is lost and all that remains is an impression of the organism in the rock—an impression fossil.If this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved.Nodules from the Carboniferous Mazon Creek fossil beds of Illinois, USA, are among the best documented examples of such mineralization.The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystalization, adpression, carbonization, and bioimmuration.
If this hole is later filled with other minerals, it is a cast.