Editing Fossil (section)

== Types ==
[[File:Index fossils.gif|upright=1.35|thumb|Examples of index fossils]]

=== Index ===
{{Main|Index fossil}}

Index fossils (also known as guide fossils, indicator fossils or zone fossils) are fossils used to define and identify [[geologic column|geologic periods]] (or faunal stages). They work on the premise that, although different [[sediment]]s may look different depending on the conditions under which they were deposited, they may include the remains of the same [[species]] of fossil. The shorter the species' time range, the more precisely different sediments can be correlated, and so rapidly evolving species' fossils are particularly useful as index fossils. 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 poor.

=== Trace ===
{{Main|Trace fossil}}

Trace fossils are fossil records of biological activity by lifeforms but not the preserved remains of the organism itself. They consist mainly of tracks and burrows, but also include [[coprolite]]s (fossil [[feces]]) and marks left by feeding.<ref name="UCMPWhatIsPaleo">{{cite web | url=http://www.ucmp.berkeley.edu/faq.php#paleo | access-date=17 September 2008 | title=What is paleontology? | publisher=University of California Museum of Paleontology | archive-url=https://web.archive.org/web/20080916013642/http://www.ucmp.berkeley.edu/faq.php#paleo | archive-date=16 September 2008 | url-status=dead }}</ref><ref name="FedonkinGehlingEtAl2007RiseOfAnimals" /> Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilized hard parts, and they reflect animal behaviours. Many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them.<ref name="Seilacher1994">e.g. {{Cite journal
| author = Seilacher, A. | year = 1994 | title = How valid is Cruziana Stratigraphy?
| journal = International Journal of Earth Sciences | volume = 83 | issue = 4 | pages = 752–758
| doi=10.1007/BF00251073 | bibcode=1994GeoRu..83..752S| s2cid = 129504434 }}</ref> Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of the appearance of moderately complex animals (comparable to [[earthworm]]s).<ref name="FedonkinGehlingEtAl2007RiseOfAnimals">{{Cite book |author1=Fedonkin, M.A. |author2=Gehling, J.G. |author3=Grey, K. |author4=Narbonne, G.M. |author5=Vickers-Rich, P. |title=The Rise of Animals: Evolution and Diversification of the Kingdom Animalia |publisher=JHU Press |year=2007 |isbn=978-0-8018-8679-9 |pages=213–216 |url=https://books.google.com/books?id=OFKG6SmPNuUC&pg=PA213 |access-date=14 November 2008 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317062706/https://books.google.com/books?id=OFKG6SmPNuUC&pg=PA213 |url-status=live }}</ref>

Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. They were first described by [[William Buckland]] in 1829. Prior to this they were known as "fossil [[conifer cone#Pinaceae cones|fir cones]]" and "[[bezoar]] stones." They serve a valuable purpose in paleontology because they provide direct evidence of the predation and diet of extinct organisms.<ref>{{cite web|url=http://dictionary.reference.com/search?q=coprolites|title=coprolites |publisher=[[Dictionary.com]] |access-date=29 February 2012|archive-url=https://web.archive.org/web/20081217091807/http://dictionary.reference.com/search?q=coprolites|archive-date=17 December 2008|url-status=live}}</ref> Coprolites may range in size from a few millimetres to over 60 centimetres.

<gallery widths="200px" heights="155px">
File:CambrianRusophycus.jpg|[[Cambrian]] [[trace fossil]]s including ''[[Rusophycus]]'', made by a [[trilobite]]
File:Coprolite.jpg|A coprolite of a carnivorous dinosaur found in southwestern [[Saskatchewan]]
File:Climactichnites wilsoni, densely packed.jpg|Densely packed, subaerial or nearshore trackways (''[[Climactichnites]] wilsoni'') made by a putative, slug-like [[mollusk]] on a Cambrian tidal flat
</gallery>

=== Transitional ===
{{Main|Transitional fossil}}
{{Further|List of transitional fossils}}

A ''transitional fossil'' is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group.<ref>{{cite book|last1=Herron|first1=Scott|last2=Freeman|first2=Jon C.|title=Evolutionary analysis|url=https://books.google.com/books?id=gnZIngEACAAJ&pg=PA816|year=2004|publisher=Pearson Education|location=Upper Saddle River, NJ|isbn=978-0-13-101859-4|page=816|edition=3rd|access-date=11 October 2018|archive-date=17 March 2023|archive-url=https://web.archive.org/web/20230317062709/https://books.google.com/books?id=gnZIngEACAAJ&pg=PA816|url-status=live}}</ref> This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation.{{clear-left}}

=== Microfossils ===
[[File:Microfossils.JPG|thumb|left|Microfossils about 1&nbsp;mm]]
{{Main|Microfossil}}
{{See also|Micropaleontology|Protists in the fossil record}}

[[Microfossil]] is a descriptive term applied to fossilized plants and animals whose size is just at or below the level at which the fossil can be analyzed by the naked eye. A commonly applied cutoff point between "micro" and [[macrofossil|"macro" fossils]] is 1&nbsp;mm. Microfossils may either be complete (or near-complete) organisms (such as the marine plankters [[foraminifera]] and [[coccolithophore]]s) or component parts (such as small teeth or [[palynology|spores]]) of larger animals or plants. Microfossils are of critical importance as a reservoir of [[Paleoclimatology|paleoclimate]] information, and are also commonly used by [[biostratigraphy|biostratigraphers]] to assist in the correlation of rock units.{{clear}}

=== Resin ===
{{Main|Amber}}

[[File:Leptofoenus pittfieldae (male) rotated.JPG|thumb|The wasp ''[[Leptofoenus pittfieldae]]'' trapped in [[Dominican amber]], from 20 to 16&nbsp;million years ago. It is known only from this specimen.]]

Fossil resin (colloquially called [[amber]]) is a natural [[polymer]] found in many types of strata throughout the world, even the [[Arctic]]. The oldest fossil resin dates to the [[Triassic]], though most dates to the [[Cenozoic]]. The excretion of resin by certain plants is thought to be an evolutionary [[adaptation]] for to protect against insects and to seal wounds. Fossil resin often contains other fossils, called inclusions, that were captured by the sticky resin. These include bacteria, fungi, other plants, and animals. Animal inclusions are usually small [[invertebrate]]s, predominantly [[arthropod]]s such as insects and spiders, and only extremely rarely a [[vertebrate]] such as a small lizard. Preservation of inclusions can be exquisite, including small fragments of [[DNA]].

=== {{anchor|derived|reworked}}Derived or reworked ===
{{See also|Zombie taxon}}

[[File:CentrumSideView.jpg|thumb|left|Eroded [[Jurassic]] [[plesiosaur]] vertebral centrum found in the Lower [[Cretaceous]] Faringdon Sponge Gravels in Faringdon, England. An example of a ''remanié'' fossil.]]

A ''derived'', ''reworked'' or {{lang|fr|remanié fossil}} is a fossil found in rock that accumulated significantly later than when the fossilized animal or plant died.<ref>{{cite book |last1=Neuendorf |first1=Klaus K. E. |last2=Institute |first2=American Geological |title=Glossary of Geology |date=2005 |publisher=Springer Science & Business Media |isbn=978-0-922152-76-6 |url=https://books.google.com/books?id=yD79FqfECCYC&pg=PA551 |language=en |access-date=7 June 2020 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317062711/https://books.google.com/books?id=yD79FqfECCYC&pg=PA551 |url-status=live }}</ref> Reworked fossils are created by erosion exhuming (freeing) fossils from the rock formation in which they were originally deposited and redepositing them in a younger sedimentary deposit.{{clear-right}}

=== Wood ===
{{Main|Fossil wood}}
{{multiple image
|direction = vertical
|image1 = Petrified forest log 2 md.jpg
|caption1 = [[Petrified wood]]. The internal structure of the tree and bark are maintained in the [[#Permineralization|permineralization]] process.
|image2 = Petrified wood close 052615.jpg
|caption2 = Polished section of petrified wood showing annual rings
}}
Fossil wood is wood that is preserved in the fossil record. Wood is usually the part of a plant that is best preserved (and most easily found). Fossil wood may or may not be [[petrified wood|petrified]]. The fossil wood may be the only part of the plant that has been preserved;<ref name="strauss">{{cite web |url=http://www.edstrauss.com/pwoodfx.html |title=Petrified Wood from Western Washington |author=Ed Strauss |year=2001 |access-date=8 April 2011 |url-status=dead |archive-url=https://web.archive.org/web/20101211224655/http://www.edstrauss.com/pwoodfx.html |archive-date=11 December 2010 }}</ref> therefore such wood may get a special kind of [[botanical name]]. This will usually include "xylon" and a term indicating its presumed affinity, such as ''[[Araucarioxylon arizonicum|Araucarioxylon]]'' (wood of ''[[Araucaria]]'' or some related genus), ''[[Palmoxylon]]'' (wood of an indeterminate [[Arecaceae|palm]]), or ''Castanoxylon'' (wood of an indeterminate [[Castanopsis|chinkapin]]).<ref name="stewart">{{cite book
|author1=Wilson Nichols Stewart |author2=Gar W. Rothwell |title =Paleobotany and the evolution of plants
|publisher =Cambridge University Press
|edition=2
|year =1993
|url={{google books |plainurl=y |id=Fhm-oed74JgC|page=31}}
|isbn =978-0-521-38294-6
|page=31
}}</ref>{{clear-left}}

=== Subfossil ===
[[File:Dodo-Skeleton Natural History Museum London England.jpg|thumb|left|A subfossil [[dodo]] skeleton]]
The term subfossil can be used to refer to remains, such as bones, nests, or [[coprolite|fecal deposits]], whose fossilization process is not complete, either because the length of time since the animal involved was living is too short or because the conditions in which the remains were buried were not optimal for fossilization.<ref>{{Cite web |title = Subfossils Collections |publisher = South Australian Museum |url = https://www.samuseum.sa.gov.au/subfossils |access-date = 28 August 2020 |archive-date = 17 April 2021 |archive-url = https://web.archive.org/web/20210417141305/https://www.samuseum.sa.gov.au/subfossils |url-status = live }}</ref> Subfossils are often found in caves or other shelters where they can be preserved for thousands of years.<ref>{{cite web
 | title = Subfossils Collections
 | publisher = South Australian Museum
 | url = http://www.samuseum.sa.gov.au/subfossils/collections
 |url-status=dead
 |archive-url=https://web.archive.org/web/20110617011415/http://www.samuseum.sa.gov.au/subfossils/collections
 |archive-date=17 June 2011 |access-date=23 January 2014
}}</ref> The main importance of subfossil vs. fossil remains is that the former contain organic material, which can be used for [[radiocarbon dating]] or extraction and [[DNA sequencing|sequencing of DNA]], [[protein sequencing|protein]], or other biomolecules. Additionally, [[isotope]] ratios can provide much information about the ecological conditions under which extinct animals lived. Subfossils are useful for studying the evolutionary history of an environment and can be important to studies in [[paleoclimatology]].

Subfossils are often found in depositionary environments, such as lake sediments, oceanic sediments, and soils. Once deposited, physical and chemical [[weathering]] can alter the state of preservation, and small subfossils can also be ingested by living [[organism]]s. Subfossil remains that date from the [[Mesozoic]] are exceptionally rare, are usually in an advanced state of decay, and are consequently much disputed.<ref>{{Cite journal | last1 = Peterson | first1 =Joseph E. | last2 = Lenczewski | first2 = Melissa E. | last3 = Scherer | first3 = Reed P. | title = Influence of Microbial Biofilms on the Preservation of Primary Soft Tissue in Fossil and Extant Archosaurs | editor-last = Stepanova | editor-first = Anna | journal = PLOS ONE | volume = 5 | issue = 10 | page = 13A |date=October 2010 | doi = 10.1371/journal.pone.0013334 | pmid=20967227 | pmc=2953520
| bibcode =2010PLoSO...513334P | doi-access =free }}</ref> The vast bulk of subfossil material comes from [[Quaternary]] sediments, including many subfossilized [[chironomid]] head capsules, [[ostracod]] [[carapace]]s, [[diatom]]s, and [[foraminifera]].

[[File:Theba geminata 08.JPG|thumb|Subfossil ''[[Theba|Theba geminata]]'']]

For remains such as molluscan [[seashell]]s, which frequently do not change their chemical composition over geological time, and may occasionally even retain such features as the original color markings for millions of years, the label 'subfossil' is applied to shells that are understood to be thousands of years old, but are of [[Holocene]] age, and therefore are not old enough to be from the [[Pleistocene]] epoch.<ref>{{cite book |last= Anand|first= Konkala|date= 2022|title= Zoology: Animal Distribution, Evolution And Development|url= https://books.google.com/books?id=NuO8EAAAQBAJ|location= |publisher= AG PUBLISHING HOUSE|page= 42|isbn=9789395936293}}</ref>

=== Chemical fossils ===
{{See also|Biosignature}}
Chemical fossils, or chemofossils, are chemicals found in rocks and [[fossil fuel]]s (petroleum, coal, and natural gas) that provide an organic signature for ancient life. [[Molecular fossil]]s and isotope ratios represent two types of chemical fossils.<ref>{{cite web|url=http://petrifiedwoodmuseum.org/ChemicalMolecularFossils.htm|title=Chemical or Molecular Fossils|website=petrifiedwoodmuseum.org|access-date=15 September 2013|archive-url=https://web.archive.org/web/20140420044014/http://petrifiedwoodmuseum.org/ChemicalMolecularFossils.htm|archive-date=20 April 2014|url-status=dead}}</ref> The oldest traces of life on Earth are fossils of this type, including carbon isotope anomalies found in [[zircon]]s that imply the existence of life as early as 4.1&nbsp;billion years ago.<ref name="AP-20151019" /><ref name="PNAS-20151014-pdf" /><!--if 4.1 is too much recentism, there's still 3.8 from zircons from the same area, see refs in lead.-->{{clear-left}}