The principle of faunal succession, also known as the law of faunal succession, is based on the observation that sedimentary rock

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

contain fossilized flora and fauna, and that these fossils succeed each other vertically in a specific, reliable order that can be identified over wide horizontal distances. A fossilized Neanderthal bone will never be found in the same stratum as a fossilized Megalosaurus, for example, because neanderthals and megalosaurs lived during different geological periods, separated by many millions of years. This allows for strata to be identified and dated by the fossils found within. This principle, which received its name from the English geologist William Smith, is of great importance in determining the relative age of rocks and strata. The fossil content of rocks together with the law of superposition helps to determine the time sequence in which sedimentary rocks were laid down. Evolution explains the observed faunal and floral succession preserved in rocks. Faunal succession was documented by Smith in England during the first decade of the 19th century, and concurrently in France by

Cuvier Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in nat ...

(with the assistance of the mineralogist

Alexandre Brongniart Alexandre Brongniart (5 February 17707 October 1847) was a French chemist, mineralogist, geologist, paleontologist, and zoologist, who collaborated with Georges Cuvier on a study of the geology of the region around Paris. Observing fossil content ...

). Archaic biological features and organisms are succeeded in the fossil record by more modern versions. For instance, paleontologists investigating the evolution of birds predicted that

feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier ...

s would first be seen in primitive forms on flightless predecessor organisms such as feathered dinosaurs. This is precisely what has been discovered in the fossil record: simple feathers, incapable of supporting flight, are succeeded by increasingly large and complex feathers. In practice, the most useful diagnostic species are those with the fastest rate of species turnover and the widest distribution; their study is termed biostratigraphy, the science of dating rocks by using the fossils contained within them. In

Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

strata, fossilized tests of foraminifera are often used to determine faunal succession on a refined scale, each biostratigraphic unit ( biozone) being a geological stratum that is defined on the basis of its characteristic fossil taxa. An outline microfaunal zonal scheme based on both foraminifera and ostracoda was compiled by M. B. Hart (1972). Earlier fossil life forms are simpler than more recent forms, and more recent fossil forms are more similar to living forms (principle of faunal succession).''Evolutionary Analysis'', 4th Edition. p 61.

References

{{Geologic Principles Paleontological concepts and hypotheses Dating methods Stratigraphy de:Biostratigraphie#Das Prinzip der Fossilfolge

See also

References