Different species of ammonites lived at different times within the Mesozoic, so identifying a fossil species can help narrow down when a rock was formed.Correlation can involve matching an undated rock with a dated one at another location.Some of the most useful fossils for dating purposes are very small ones.For example, microscopic dinoflagellates have been studied and dated in great detail around the world.Very rare, and typically found in very recent fossils.Some examples include freezing (woolly mammoths in the permafrost), mummification, fossilization in amber.
Many traces date from significantly earlier than the body fossils of the animals suspected to have made them. Permineralization can preserve even the most minute details including cell structure.
Authigenic Mineralisation - A very special form of cast and mold formation where a nodule is formed around the fossil by minerals such as siderite.
In cases of rapid fosssilization, very fine details can be preserved.
Throughout the history of life, different organisms have appeared, flourished and become extinct.
Many of these organisms have left their remains as fossils in sedimentary rocks.