Benthic foraminifera have been used for paleobathymetry since the 1930's and modern studies utilize a variety of techniques to reconstruct paleodepths. Living forams, which came into existence during the Carboniferous, occur most abundantly in the shelf regions of most tropical and subtropical shallow marine environments (carbonate rich). Because of their complexity, which aids in identification and their diversity in the shelf environments, larger foraminifera fossils provide clues to paleoenvironments and biostratigraphy of the shelf limestones around the world. Macrofossils are rare in habitats such as these so forams provide a great advantage. Additionally, foraminifera provide biostratigraphic markers and because the fossil record is so rich in these fossils, the evolutionary theory can be applied since horizontal and vertical variation can be studied directly in the stratigraphic record. Many suborders are still extant, so current processes can be studied and used to infer back to fossil forams.
Foraminifera can vary in size from microscopic to several centimeters
Variations in the water temperature inferred from oxygen isotopes from the test calcite can be used to reconstruct paleo-oceanographic conditions by careful comparison of changes in oxygen isotope levels as seen in benthic forms (for bottom waters) and planktic forms (for mid to upper waters). This type of study has allowed the reconstruction of oceanic conditions during the Eocene-Oligocene, the Miocene and the Quaternary. The positive correlation between test wall type, paleodepths and salinity has been noted in modern foraminifera.