A microfossil is a fossil with a size between three hundredths of a millimeter and one millimeter. Such remnants of the microcosm are examined in the context of Micropaleontology by the methods of light microscopy, magnification factor lies mostly between 5 and 100 The limits to the smaller nannofossils and the larger macro fossils are fluid.
The microfossils include - apart from the large Foraminifera - including " protists " ( single-celled with nucleus ), Tintinniden, ostracods, Tentakuliten and with appropriate size to isolated remnants of larger organisms such as sponge spicules, and conodonts otoliths ( ear bones ), fish scales, teeth and other remains small vertebrates ( Mikrovertebraten ).
Microfossils are indispensable for the relative age determination ( biostratigraphy ) of sedimentary rocks from the Cambrian (small shelly fauna ) until today. In addition, they are important signs for the reconstruction of the distribution of land and sea ( paleogeography ), for the exploration of the oceans ( palaeo-oceanography ), for the description of fossil aquatic habitats ( palaeoenvironmental ) and for the climate history ( paleoclimatology ) of the earth. Using the temperature-dependent discoloration of conodonts ( Conodont alteration index) allows the thermal fate of sedimentary rocks understand, a circumstance that in the search ( prospecting ) for oil and natural gas deposits in applied geology ( geology ) is of importance.