Index fossil
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225440809
2008-07-13T18:34:52Z
PalaeoMal
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/* 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 ===
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[[Category:{{{1|}}} articles with sections needing expansion]]
[[Category:Fossils]]
[[Category:Paleontology]]
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[[ja:示準化石]]
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