Faunal dating

These Late Pleistocene food sources included mammoths, mastodon; giant bison, sloths, camels, and diprotodons.The term also covers extinct larger species of quite small animals, such as giant beavers.The longer lived the species, the poorer the stratigraphic precision, so fossils that evolve rapidly, such as ammonites, are favoured over forms that evolve much more slowly, like nautiloids.Often biostratigraphic correlations are based on a fauna, not an individual species, as this allows greater precision.Usually the aim is correlation, demonstrating that a particular horizon in one geological section represents the same period of time as another horizon at some other section.The fossils are useful because sediments of the same age can look completely different because of local variations in the sedimentary environment.

For instance, the presence of the trace fossil Treptichnus pedum was used to define the base of the Cambrian period, but it has since been found in older strata.French palaeontologist Alcide d'Orbigny is credited for the invention of this concept.He named stages after geographic localities with particularly good sections of rock strata that bear the characteristic fossils on which the stages are based.Fossil assemblages were traditionally used to designate the duration of periods.Since a large change in fauna was required to make early stratigraphers create a new period, most of the periods we recognise today are terminated by a major extinction event or faunal turnover.For example, one section might have been made up of clays and marls while another has more chalky limestones, but if the fossil species recorded are similar, the two sediments are likely to have been laid down at the same time.Biostratigraphy originated in the early 19th century, where geologists recognised that the correlation of fossil assemblages between rocks of similar type but different age decreased as the difference in age increased.Index fossils are one of the species from the assemblage of species that characterise the zone. Its thickness range from a few to hundreds of metres, and its extant range from local to worldwide.SYNONYMS OR RELATED TERMS: mega-fauna CATEGORY: fauna DEFINITION: The large, Ice Age big-game fauna in North America, now extinct.The late Pleistocene extinction of megafauna did not occur synchronously nor was it of equal magnitude throughout the world.Considerable doubt exists regarding the timing of the megafaunal extinction on various landmasses.

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  1. The principle of faunal succession. their study is termed biostratigraphy, the science of dating rocks by using the fossils contained within them. In.

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