Index fossil 45930 225440809 2008-07-13T18:34:52Z PalaeoMal 3955563 /* Common Index Fossils */ Viviparus added [[Image:Index_fossils.gif|right|thumb|200px|example index fossils]] '''Index fossils''' (also known as guide fossils or zone fossils) are [[fossil]]s used to define and identify [[geologic column|geologic period]]s (or faunal stages). They work on the premise that, although different [[sediment]]s may look different depending on the conditions under which they were laid down, they may include the remains of the same [[species]] of fossil. If the species concerned were short-lived (in geological terms, lasting a few hundred thousand years), then it is certain that the sediments in question were deposited within that narrow time period. The shorter the lifespan of a species, the more precisely different sediments can be correlated, and so rapidly evolving types of fossils are particularly valuable. The best index fossils are common, easy-to-identify at species level, and have a broad distribution—otherwise the likelihood of finding and recognizing one in the two sediments is low. [[Ammonite]]s fit these demands well, and are the best-known fossils that have been widely used for this. Other important groups that provide index fossils are the [[coral]]s, [[graptolite]]s, [[brachiopod]]s, [[trilobite]]s, and echinoids ([[sea urchin]]s). [[Conodont]]s may be identified by experts using light [[microscopy]] such that they can be used to index a given sample with good resolution. [[Fossilized]] [[teeth]] of [[mammal]]s, have also been used. [[Geologist]]s use both large fossils (called macrofossils) and microscopic fossils (called microfossils) for this process, known as [[biostratigraphy]]. Macrofossils have the advantage of being easy to see in the field, but they are rarer, and microfossils are very commonly used by [[Petroleum|oil]] prospectors and other industries interested in [[mineral]] resources when accurate knowledge of the age of the rocks being looked at is needed. === Common Index Fossils === <center> {| class="wikitable" align="center" |+ List of Common Index Fossils <ref name="USGS_indexfossils">[http://pubs.usgs.gov/gip/geotime/fossils.html Index Fossils], from the [[US Geological Survey]]. Updated [[July 28]], [[1997]].</ref> ! Fossil !! Scientific Name !! Time Period !! Million Years Ago |- |[[Image:Calico scallop 02.jpg|120px]]<br/>[[Argopectin gibbus|Calico Scallop]]|| ''[[Pecten gibbus]]''<br/>''[[Argopectin gibbus]]'' || [[Quaternary Period]] || {{Ma|1.8}} |- | || ''[[Neptunea tabulata]]'' || [[Quaternary Period]] || {{Ma|1.8}} |- | [[Image:Viviparus glacialis - Rosmalen - Late Tiglian.jpg|120px]]|| ''[[Viviparus glacialis]]'' || [[Tiglian]] ([[Early Pleistocene]]) || {{Ma|2.3-1.8}} |- | || ''[[Calyptatraphorus velatus]]'' || [[Tertiary Period]] || |- | || ''[[Venericardia planicosta]]'' || [[Eocene]] || |- |[[Image:SmallScaphites.jpg|120px]]<br/>[[Scaphites]] || ''[[Scaphites hippocrepis]]'' || [[Cretaceous Period]] || {{Ma|Cretaceous|{{period end|Cretaceous}}}} |- |[[Inoceramus]] ||''[[Inoceramus labiatus]]'' || [[Cretaceous Period]] || |- |[[Perisphinctes]] || ''[[Perisphinctes tiziani]]'' || [[Jurassic Period]] || |- | || ''[[Nerinea trinodosa]]'' || [[Jurassic Period]] || |- | || ''[[Trophites subbullatus]]'' || [[Triassic Period]] || |- | || ''[[Monotis subcircularis]]'' || [[Triassic Period]] || |- | || ''[[Leptodus americanus]]'' || [[Permian Period]] || |- |[[Parafusulina]] || ''[[Parafusulina bosei]]'' || [[Permian Period]] || |- | || ''[[Dictyoclostus americanus]]'' || [[Pennsylvanian Period]] || |- | || ''[[Lophophyllidium proliferum]]'' || [[Pennsylvanian Period]] || |- | || ''[[Cactocrinus multibrachiatus]]'' || [[Mississippian Period]] || |- | || ''[[Prolecanites gurleyi]]'' || [[Mississippian Period]] || |- |[[Image:MucrospiriferSp.jpg|120px]]<br/>[[Mucrospirifer]] || ''[[Mucrospirifer mucronatus]]'' || [[Devonian Period]] || {{Ma|416|359}} |- | || ''[[Palmatolepus unicornis]]'' || [[Devonian Period]] || |- |[[Image:Ammonite Jeletzkytes.jpg|120px]]<br/>[[Ammonite]]|| ''[[Ammonite jeletzkytes]]'' || Late [[Silurian]] to Early [[Devonian]] || {{Ma|400}} |- | || ''[[Cystiphyllum niagarense]]'' || [[Silurian Period]] || |- | || ''[[Hexamoceras hertzeri]]'' || [[Silurian Period]] || |- | [[Trilobite]] || ''[[Bathyurus extans]]'' || [[Ordovician Period]] || |- | || ''[[Tetragraptus fructicosus]]'' || [[Ordovician Period]] || |- | || ''[[Paradoxides pinus]]'' || [[Cambrian period]] || |- |[[Image:Asaphiscuswheelerii.jpg |120px]]<br/>[[Trilobite]]|| See [[list of trilobites]] || [[Cambrian Period]] || {{Ma|540}} |- | || ''[[Billingselia corrugata]]'' || [[Cambrian Period]] || |- |} </center> === In Popular Culture === Musical Group [[Bad Religion]] have a song titled "Part IV (The Index Fossil)" on their 1988 album ''[[Suffer (album)|Suffer]]''. The song suggests that one day [[human|humanity]] will be "an index fossil buried in [its] own debris". === References and Links === <references /> [[Category:{{{1|}}} articles with sections needing expansion]] [[Category:Fossils]] [[Category:Paleontology]] [[de:Leitfossil]] [[es:Fósil director]] [[hu:Jelzőfosszília]] [[nl:Gidsfossiel]] [[ja:示準化石]] [[nds:Leddfossil]] [[pl:Skamieniałość przewodnia]] [[pt:Fóssil de idade]] [[zh:指準化石]]