Editing Fossil

{{Short description|Preserved remains or traces of organisms from a past geological age}}
{{Redirect|Dinosaur bones|the band |Dinosaur Bones||Fossil (disambiguation)}}
{{Redirect|Fossilization|the linguistics term|Fossilization (linguistics)}}
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[[File:Fossil Diversity.png|thumb|300px|Montage of animal fossils. Clockwise from top left: ''[[Onychocrinus]]'' and ''[[Palaeosinopa]]''; bottom row: ''[[Gryphaea]]'' and ''[[Harpactocarcinus]]'']]

A '''fossil''' (from [[Classical Latin]] {{wikt-lang|la|fossilis}}, {{lit|obtained by digging}})<ref>{{cite book|title=Oxford English Dictionary|publisher=Oxford University Press|url=http://www.oed.com/|access-date=17 June 2013|archive-url=https://web.archive.org/web/20080111125659/http://www.oed.com/|archive-date=11 January 2008|url-status=live}}</ref> is any preserved remains, impression, or trace of any once-living thing from a past [[geological age]]. Examples include [[bone]]s, [[seashell|shells]], [[exoskeleton]]s, stone imprints of animals or [[microbe]]s, objects preserved in [[#Resin|amber]], [[hair]], [[petrified wood]] and [[DNA]] remnants. The totality of fossils is known as the ''fossil record''. Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give a good understanding of the pattern of diversification of life on Earth.<ref name="Jablonski2003">{{Cite journal |last1=Jablonski |first1=David |last2=Roy |first2=Kaustuv |last3=Valentine |first3=James W. |last4=Price |first4=Rebecca M. |last5=Anderson |first5=Philip S. |date=2003-05-16 |title=The impact of the pull of the recent on the history of marine diversity |url=https://pubmed.ncbi.nlm.nih.gov/12750517/ |journal=Science |volume=300 |issue=5622 |pages=1133–1135 |doi=10.1126/science.1083246 |issn=1095-9203 |pmid=12750517 |bibcode=2003Sci...300.1133J |s2cid=42468747 |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215055227/https://pubmed.ncbi.nlm.nih.gov/12750517/ |url-status=live }}</ref><ref>{{Cite journal |last1=Sahney |first1=Sarda |last2=Benton |first2=Michael J. |last3=Ferry |first3=Paul A. |date=2010-08-23 |title=Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land |journal=Biology Letters |volume=6 |issue=4 |pages=544–547 |doi=10.1098/rsbl.2009.1024 |pmc=2936204 |pmid=20106856}}</ref><ref name= "sb2017">{{Cite journal |last1=Sahney |first1=Sarda |last2=Benton |first2=Michael |date=2017 |title=The impact of the Pull of the Recent on the fossil record of tetrapods |url=https://cpb-eu-w2.wpmucdn.com/blogs.bristol.ac.uk/dist/5/537/files/2021/01/2017Sahney.pdf |journal=Evolutionary Ecology Research |volume=18 |pages=7–23 |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215043633/https://cpb-eu-w2.wpmucdn.com/blogs.bristol.ac.uk/dist/5/537/files/2021/01/2017Sahney.pdf |url-status=live }}</ref> In addition, the record can predict and fill gaps such as the discovery of ''[[Tiktaalik]]'' in the arctic of [[Canada]].<ref name="Nature">{{cite journal |author=Edward B. Daeschler, Neil H. Shubin and Farish A. Jenkins Jr. |date=6 April 2006 |title=A Devonian tetrapod-like fish and the evolution of the tetrapod body plan |url=http://www.stuartsumida.com/BIOL524/DaeschlerEtAl2006.pdf |journal=[[Nature (journal)|Nature]] |volume=440 |issue=7085 |pages=757–763 |bibcode=2006Natur.440..757D |doi=10.1038/nature04639 |pmid=16598249 |doi-access=free |access-date=15 December 2022 |archive-date=15 December 2022 |archive-url=https://web.archive.org/web/20221215064732/http://www.stuartsumida.com/BIOL524/DaeschlerEtAl2006.pdf |url-status=live }}</ref>

[[Paleontology]] includes the study of fossils: their age, method of formation, and [[evolution]]ary significance. Specimens are sometimes considered to be fossils if they are over 10,000 years old.<ref>{{Cite journal |last1=Bertling |first1=M |last2=Braddy |first2=S |display-authors=1 |date=2006 |title=Names for trace fossils: a uniform approach |url=https://doi.org/10.1080/00241160600787890 |journal=Lethaia |volume=39 |issue=3 |pages=265–286|doi=10.1080/00241160600787890 |bibcode=2006Letha..39..265B |hdl=11336/16772 |hdl-access=free }}</ref><ref>{{Cite journal |last1=Bertling |first1=M |last2=Buatois |first2=L |display-authors=1 |date=2022 |title=Names for trace fossils 2.0: theory and practice in ichnotaxonomy |url=https://doi.org/10.18261/let.55.3.3 |journal=Lethaia |volume=55 |issue=3 |pages=1–19|doi=10.18261/let.55.3.3 |bibcode=2022Letha..55..3.3B }}</ref><ref>{{cite web |url=http://www.sdnhm.org/science/paleontology/resources/frequent/ |title=theNAT :: San Diego Natural History Museum :: Your Nature Connection in Balboa Park :: Frequently Asked Questions |publisher=Sdnhm.org |access-date=5 November 2012 |archive-url=https://web.archive.org/web/20120510101706/http://sdnhm.org/science/paleontology/resources/frequent/ |archive-date=10 May 2012 |url-status=dead }}</ref> The oldest fossils are around 3.48&nbsp;billion years <ref name="AP-20131113">{{cite news |last=Borenstein |first=Seth |title=Oldest fossil found: Meet your microbial mom |url=http://apnews.excite.com/article/20131113/DAA1VSC01.html |date=13 November 2013 |agency=Associated Press |access-date=15 November 2013 |archive-url=https://web.archive.org/web/20150629230719/http://apnews.excite.com/article/20131113/DAA1VSC01.html |archive-date=29 June 2015 |url-status=live }}</ref><ref name="AST-20131108">{{cite journal |last1=Noffke |first1=Nora |author1-link=Nora Noffke |last2=Christian |first2=Daniel |last3=Wacey |first3=David |last4=Hazen |first4=Robert M. |title=Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia |date=8 November 2013 |journal=[[Astrobiology (journal)|Astrobiology]] |doi=10.1089/ast.2013.1030 |volume=13 |issue=12 |pages=1103–24 |bibcode=2013AsBio..13.1103N |pmid=24205812 |pmc=3870916}}</ref><ref>{{cite news | author = Brian Vastag | title = Oldest 'microfossils' raise hopes for life on Mars | date = 21 August 2011 | url = https://www.washingtonpost.com/national/health-science/oldest-microfossils-hail-from-34-billion-years-ago-raise-hopes-for-life-on-mars/2011/08/19/gIQAHK8UUJ_story.html?hpid=z3 | newspaper = The Washington Post | access-date = 21 August 2011 | archive-url = https://web.archive.org/web/20111019000458/http://www.washingtonpost.com/national/health-science/oldest-microfossils-hail-from-34-billion-years-ago-raise-hopes-for-life-on-mars/2011/08/19/gIQAHK8UUJ_story.html?hpid=z3 | archive-date = 19 October 2011 | url-status = live }}<br />{{cite news | first = Nicholas | last = Wade | title = Geological Team Lays Claim to Oldest Known Fossils | date = 21 August 2011 | url = https://www.nytimes.com/2011/08/22/science/earth/22fossil.html?_r=1&partner=rss&emc=rss&src=ig | work = The New York Times | access-date = 21 August 2011 | archive-url = https://web.archive.org/web/20130501085118/http://www.nytimes.com/2011/08/22/science/earth/22fossil.html?_r=1&partner=rss&emc=rss&src=ig | archive-date = 1 May 2013 | url-status = live }}</ref> to 4.1&nbsp;billion years old.<ref name="AP-20151019">{{cite news |last=Borenstein |first=Seth |title=Hints of life on what was thought to be desolate early Earth |url=http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |date=19 October 2015 |work=[[Excite (web portal)|Excite]] |location=Yonkers, NY |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |access-date=20 October 2015 |archive-url=https://web.archive.org/web/20151023200248/http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |archive-date=23 October 2015 |url-status=live }}</ref><ref name="PNAS-20151014-pdf">{{cite journal |last1=Bell |first1=Elizabeth A. |last2=Boehnike |first2=Patrick |last3=Harrison |first3=T. Mark |last4=Mao |first4=Wendy L. |display-authors=3 |date=19 October 2015 |title=Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon |url=http://www.pnas.org/content/early/2015/10/14/1517557112.full.pdf |journal=Proc. Natl. Acad. Sci. U.S.A. |doi=10.1073/pnas.1517557112 |issn=1091-6490 |access-date=20 October 2015 |pmid=26483481 |pmc=4664351 |volume=112 |issue=47 |pages=14518–21 |bibcode=2015PNAS..11214518B |archive-url=https://web.archive.org/web/20151106021508/http://www.pnas.org/content/early/2015/10/14/1517557112.full.pdf |archive-date=6 November 2015 |url-status=live |doi-access=free }} Early edition, published online before print.</ref> The observation in the 19th century that certain fossils were associated with certain rock [[stratum|strata]] led to the recognition of a [[geological timescale]] and the [[relative dating|relative ages]] of different fossils. The development of [[radiometric dating]] techniques in the early 20th century allowed scientists to quantitatively measure the [[absolute dating|absolute ages]] of rocks and the fossils they host.

There are many processes that lead to '''[[wikt:Special:Search/fossilize|fossilization]]''', including [[permineralization]], casts and molds, [[authigenesis|authigenic mineralization]], replacement and recrystallization, adpression, [[carbonization]], and bioimmuration.

Fossils vary in size from one-[[micrometre]] (1&nbsp;μm) bacteria<ref>{{cite journal |last1 = Westall |first1 = Frances |title = Early Archean fossil bacteria and biofilms in hydrothermally influenced sediments from the Barberton greenstone belt, South Africa |journal = Precambrian Research |volume = 106 |issue = 1–2 |pages = 93–116 |doi = 10.1016/S0301-9268(00)00127-3 |year = 2001 |display-authors = 1 |last2 = De Wit |first2 = Maarten J |last3 = Dann |first3 = Jesse |last4 = Van Der Gaast |first4 = Sjerry |last5 = De Ronde |first5 = Cornel E.J |last6 = Gerneke |first6 = Dane|bibcode = 2001PreR..106...93W }}</ref> to [[dinosaur]]s and trees, many meters long and weighing many tons. The largest presently known is a ''[[Sequoia (genus)|Sequoia]]'' sp. measuring 295 feet (88 meters) in length at Coaldale, Nevada.<ref>{{cite book | editor= Donald McFarlan and Norris McWhirter | date= 1989 | title= Guinness Book of Records - 1990 | location= London | publisher= Guinness Superlatives Ltd. | page= 50 }}</ref> A fossil normally preserves only a portion of the deceased organism, usually that portion that was partially [[Mineralization (biology)|mineralized]] during life, such as the bones and teeth of [[vertebrate]]s, or the [[chitin]]ous or [[calcareous]] exoskeletons of [[invertebrate]]s. Fossils may also consist of the marks left behind by the organism while it was alive, such as [[animal track]]s or [[feces]] ([[coprolite]]s). These types of fossil are called [[trace fossil]]s or ''ichnofossils'', as opposed to ''body fossils''. Some fossils are [[biochemistry|biochemical]] and are called ''chemofossils'' or [[biosignature]]s.

{{Paleontology}}
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== History of study ==
{{Main|History of paleontology}}
{{For timeline|Timeline of paleontology}}

Gathering fossils dates at least to the beginning of recorded history. The fossils themselves are referred to as the fossil record. The fossil record was one of the early sources of data underlying the study of [[evolution]] and continues to be relevant to the [[Timeline of evolution|history of life on Earth]]. [[Paleontologist]]s examine the fossil record to understand the process of evolution and the way particular [[species]] have evolved.

=== Ancient civilizations ===
[[File:hyperborean-gryphon-persepolis-protoceratops-psittacosaurus-skeletons.jpg|thumb|right|Ceratopsian skulls are common in the [[Dzungarian Gate]] mountain pass in Asia, an area once famous for gold mines, as well as its endlessly cold winds. This has been attributed to legends of both gryphons and the land of Hyperborea.]]
Fossils have been visible and common throughout most of natural history, and so documented human interaction with them goes back as far as recorded history, or earlier.

There are many examples of [[Paleolithic]] stone knives in Europe, with fossil [[echinoderm]]s set precisely at the hand grip, dating back to ''[[Homo heidelbergensis]]'' and [[Neanderthal]]s.<ref name=prehistoric /> These ancient peoples also drilled holes through the center of those round fossil shells, apparently using them as beads for necklaces.

The ancient Egyptians gathered fossils of species that resembled the bones of modern species they worshipped. The god [[Set (deity)|Set]] was associated with the [[hippopotamus]], therefore fossilized bones of hippo-like species were kept in that deity's temples.<ref>{{Cite web |url=http://www.wondersandmarvels.com/2016/09/ancient-egyptians-collected-fossils.html |title=Ancient Egyptians Collected Fossils |access-date=9 February 2019 |archive-url=https://web.archive.org/web/20190210044430/http://www.wondersandmarvels.com/2016/09/ancient-egyptians-collected-fossils.html |archive-date=10 February 2019 |url-status=dead |date=5 September 2016 }}</ref> Five-rayed fossil sea urchin shells were associated with the deity [[Sopdu]], the Morning Star, equivalent of [[Venus (mythology)|Venus]] in Roman mythology.<ref name=prehistoric />

[[File:Micraster coranguinum.4 - Cretacico superior.JPG|thumb|right|Fossil shells from the [[cretaceous]] era sea urchin, [[Micraster]], were used in medieval times as both shepherd's crowns to protect houses, and as painted fairy loaves by bakers to bring luck to their bread-making.]]
Fossils appear to have directly contributed to the mythology of many civilizations, including the ancient Greeks. Classical Greek historian [[Herodotos]] wrote of an area near [[Hyperborea]] where [[gryphon]]s protected golden treasure. There was indeed gold mining [[Dzungarian Gate#Hyperborean connection|in that approximate region]], where beaked ''[[Protoceratops]]'' skulls were common as fossils.

A later [[Ancient Greece|Greek]] scholar, [[Aristotle]], eventually realized that fossil seashells from rocks were similar to those found on the beach, indicating the fossils were once living animals. He had previously explained them in terms of [[vapor]]ous [[exhalation]]s,<ref>{{Cite book|via=The Internet Classics Archive | title=[[Meteorology (Aristotle)|Meteorology]]
| author=Aristotle
| author-link=Aristotle
| translator= E. W. Webster
| orig-year = 350 {{sc|BCE}}
 | year = 1931
| chapter = Book {{sc|iii}} part 6
|chapter-url=http://classics.mit.edu/Aristotle/meteorology.3.iii.html|access-date=2023-02-20|archive-date=18 February 2014|archive-url=https://web.archive.org/web/20140218151153/http://classics.mit.edu/Aristotle/meteorology.3.iii.html|url-status=live}}</ref> which [[Persia]]n polymath [[Avicenna]] modified into the theory of [[Petrifaction|petrifying]] [[fluid]]s ({{lang|la|succus lapidificatus}}). Recognition of fossil seashells as originating in the sea was built upon in the 14th century by [[Albert of Saxony (philosopher)|Albert of Saxony]], and accepted in some form by most [[naturalist]]s by the 16th century.<ref>{{Cite book|title=The Meaning of Fossils: Episodes in the History of Palaeontology|first=M. J. S.|last=Rudwick|year=1985|publisher=[[University of Chicago Press]]|url=https://books.google.com/books?id=-NuYXr8BszwC&pg=PA24|isbn=978-0-226-73103-2|page=24|access-date=11 October 2018|archive-date=17 March 2023|archive-url=https://web.archive.org/web/20230317062708/https://books.google.com/books?id=-NuYXr8BszwC&pg=PA24|url-status=live}}</ref>

Roman naturalist [[Pliny the Elder]] wrote of "[[tongue stone]]s", which he called [[glossopetra]]. These were fossil shark teeth, thought by some classical cultures to look like the tongues of people or snakes.<ref name=sharkteeth /> He also wrote about the [[horns of Ammon]], which are fossil [[ammonite]]s, whence the group of shelled octopus-cousins ultimately draws its modern name. Pliny also makes one of the earlier known references to [[toadstone]]s, thought until the 18th century to be a magical cure for poison originating in the heads of toads, but which are fossil teeth from ''[[Lepidotes]]'', a [[Cretaceous]] ray-finned fish.<ref>{{Cite web |url=http://www.gwydir.demon.co.uk/jo/fossils/pliny.htm |title=References to fossils by Pliny the Elder |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20190102155131/http://gwydir.demon.co.uk/jo/fossils/pliny.htm |archive-date=2 January 2019 |url-status=dead }}</ref>

The [[Plains tribes]] of North America are thought to have similarly associated fossils, such as the many intact pterosaur fossils naturally exposed in the region, with their own mythology of the [[thunderbird (mythology)|thunderbird]].<ref>{{Cite book|url=https://books.google.com/books?id=jb9dAQAAQBAJ&q=fossil+legends+of+the+first+americans|title=Fossil Legends of the First Americans|first=Adrienne|last=Mayor|date=24 October 2013|publisher=Princeton University Press|access-date=18 October 2019|via=Google Books|isbn=978-1-4008-4931-4|archive-date=17 March 2023|archive-url=https://web.archive.org/web/20230317062708/https://books.google.com/books?id=jb9dAQAAQBAJ&q=fossil+legends+of+the+first+americans|url-status=live}}</ref>

There is no such direct mythological connection known from prehistoric Africa, but there is considerable evidence of tribes there excavating and moving fossils to ceremonial sites, apparently treating them with some reverence.<ref>{{Cite web |url=http://theconversation.com/how-we-know-that-ancient-african-people-valued-fossils-and-rocks-110321 |title=How we know that ancient African people valued fossils and rocks |date=29 January 2019 |access-date=9 February 2019 |archive-url=https://web.archive.org/web/20190210152607/http://theconversation.com/how-we-know-that-ancient-african-people-valued-fossils-and-rocks-110321 |archive-date=10 February 2019 |url-status=live }}</ref>

In Japan, fossil shark teeth were associated with the mythical [[tengu]], thought to be the razor-sharp claws of the creature, documented some time after the 8th century AD.<ref name=sharkteeth>{{Cite web |url=http://www.gwydir.demon.co.uk/jo/fossils/cartilage.htm |title=Cartilaginous fish |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20170730044544/http://gwydir.demon.co.uk/jo/fossils/cartilage.htm |archive-date=30 July 2017 |url-status=dead }}</ref>

In medieval China, the fossil bones of ancient mammals including ''[[Homo erectus]]'' were often mistaken for "[[dragon]] bones" and used as medicine and [[aphrodisiac]]s. In addition, some of these fossil bones are collected as "art" by scholars, who left scripts on various artifacts, indicating the time they were added to a collection. One good example is the famous scholar [[Huang Tingjian]] of the [[Song dynasty]] during the 11th century, who kept a specific seashell fossil with his own poem engraved on it.<ref>{{cite news |url=http://culture.people.com.cn/BIG5/n/2013/0517/c22219-21521301.html |title=4億年前"書法化石"展出 黃庭堅曾刻下四行詩[圖] |trans-title=400 million-year-old fossil appeared in exhibition with poem by Huang Tingjian |date=17 May 2013 |access-date=7 June 2018 |newspaper=[[People's Daily|People's Daily Net]] |language=zh-hant |archive-url=https://web.archive.org/web/20180612141515/http://culture.people.com.cn/BIG5/n/2013/0517/c22219-21521301.html |archive-date=12 June 2018 |url-status=live }}</ref> In his ''[[Dream Pool Essays]]'' published in 1088, Song dynasty Chinese [[scholar-official]] [[Shen Kuo]] hypothesized that marine fossils found in a [[stratum|geological stratum]] of mountains located hundreds of miles from the [[Pacific Ocean]] was evidence that a prehistoric seashore had once existed there and [[Geomorphology|shifted over centuries of time]].<ref>Sivin, Nathan (1995). ''Science in Ancient China: Researches and Reflections''. Brookfield, Vermont: VARIORUM, Ashgate Publishing. III, p. 23</ref><ref name=nj>Needham, Joseph. (1959). ''Science and Civilization in China: Volume 3, Mathematics and the Sciences of the Heavens and the Earth''. [[Cambridge University Press]]. pp. 603–618.</ref> His observation of [[petrified]] [[bamboo]]s in the dry northern climate zone of what is now [[Yan'an]], [[Shaanxi]] province, China, led him to advance early ideas of gradual [[climate change (general concept)|climate change]] due to bamboo naturally growing in wetter climate areas.<ref name=nj /><ref>Chan, Alan Kam-leung and Gregory K. Clancey, Hui-Chieh Loy (2002). ''Historical Perspectives on East Asian Science, Technology and Medicine''. Singapore: [[Singapore University Press]]. p. 15. {{ISBN|9971-69-259-7}}.</ref><ref name="Rafferty 2012 p. 6">Rafferty, John P. (2012). ''Geological Sciences; Geology: Landforms, Minerals, and Rocks''. New York: Britannica Educational Publishing, p. 6. {{ISBN|9781615305445}}</ref>

In medieval [[Christendom]], fossilized sea creatures on mountainsides were seen as proof of the biblical deluge of [[Noah's Ark]]. After observing the existence of seashells in mountains, the [[List of ancient Greek philosophers|ancient Greek philosopher]] [[Xenophanes]] (c. 570 – 478 BC) speculated that the world was once inundated in a great flood that buried living creatures in drying mud.<ref>Desmond, Adrian. "The Discovery of Marine Transgressions and the Explanation of Fossils in Antiquity", ''American Journal of Science'', 1975, Volume 275: 692–707.</ref><ref name="Rafferty 2012 pp 5–6">Rafferty, John P. (2012). ''Geological Sciences; Geology: Landforms, Minerals, and Rocks''. New York: Britannica Educational Publishing, pp. 5–6. {{ISBN|9781615305445}}.</ref>

In 1027, the [[Persian people|Persian]] [[Avicenna]] explained fossils' stoniness in ''[[The Book of Healing]]'':

{{blockquote|If what is said concerning the petrifaction of animals and plants is true, the cause of this (phenomenon) is a powerful mineralizing and petrifying virtue which arises in certain stony spots, or emanates suddenly from the earth during earthquake and subsidences, and petrifies whatever comes into contact with it. As a matter of fact, the petrifaction of the bodies of plants and animals is not more extraordinary than the transformation of waters.<ref>{{cite book|title=Science, optics, and music in medieval and early modern thought|author=Alistair Cameron Crombie|publisher=Continuum International Publishing Group|year=1990|url=https://books.google.com/books?id=zWrH7h9jNgUC&pg=PA108|isbn=978-0-907628-79-8|pages=108–109|access-date=11 October 2018|archive-date=17 March 2023|archive-url=https://web.archive.org/web/20230317062732/https://books.google.com/books?id=zWrH7h9jNgUC&pg=PA108|url-status=live}}</ref>}}

From the 13th century to the present day, scholars pointed out that the fossil skulls of [[Deinotherium giganteum]], found in [[Crete]] and Greece, might have been interpreted as being the skulls of the [[Cyclopes]] of [[Greek mythology]], and are possibly the origin of that Greek myth.<ref>{{Cite web |url=https://www.nationalgeographic.com/science/2003/02/news-deinotherium-fossils-crete-mythology-paleontology/ |title=Cyclops Myth Spurred by 'One-Eyed' Fossils? |website=[[National Geographic Society]] |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20190217030312/https://www.nationalgeographic.com/science/2003/02/news-deinotherium-fossils-crete-mythology-paleontology/ |archive-date=17 February 2019 |url-status=dead |date=5 February 2003 }}</ref><ref>{{Cite web |url=http://mentalfloss.com/article/64093/8-types-imaginary-creatures-discovered-fossils |title=8 Types of Imaginary Creatures "Discovered" In Fossils |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20190216044433/http://mentalfloss.com/article/64093/8-types-imaginary-creatures-discovered-fossils |archive-date=16 February 2019 |url-status=dead |date=19 May 2015 }}</ref> Their skulls appear to have a single eye-hole in the front, just like their modern [[elephant]] cousins, though in fact it's actually the opening for their trunk.

In [[Norse mythology]], echinoderm shells (the round five-part button left over from a sea urchin) were associated with the god [[Thor]], not only being incorporated in [[Thunderstone (folklore)#Fossils as thunderstones|thunderstones]], representations of Thor's hammer and subsequent hammer-shaped crosses as Christianity was adopted, but also kept in houses to garner Thor's protection.<ref name=prehistoric>{{Cite web |url=https://www.geolsoc.org.uk/Geoscientist/Archive/June-2012/Prehistoric-fossil-collectors |title=Prehistoric Fossil Collectors |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20190217090444/https://www.geolsoc.org.uk/Geoscientist/Archive/June-2012/Prehistoric-fossil-collectors |archive-date=17 February 2019 |url-status=live }}</ref>

These grew into the [[shepherd's crown]]s of English folklore, used for decoration and as good luck charms, placed by the doorway of homes and churches.<ref name=echinoderm>{{Cite web |url=https://depositsmag.com/2017/04/04/folklore-of-fossil-echinoderms/ |title=Folklore of Fossil Echinoderms |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20190217142211/https://depositsmag.com/2017/04/04/folklore-of-fossil-echinoderms/ |archive-date=17 February 2019 |url-status=live |date=4 April 2017 }}</ref> In [[Suffolk]], a different species was used as a good-luck charm by bakers, who referred to them as [[fairy loaf|fairy loaves]], associating them with the similarly shaped loaves of bread they baked.<ref>{{Cite journal |url=http://sp.lyellcollection.org/content/273/1/279 |title=Shepherds' crowns, fairy loaves and thunderstones: the mythology of fossil echinoids in England |journal=Geological Society, London, Special Publications |volume=273 |issue=1 |pages=279–294 |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20190221225625/http://sp.lyellcollection.org/content/273/1/279 |archive-date=21 February 2019 |url-status=dead |doi=10.1144/GSL.SP.2007.273.01.22 |year=2007 |last1=McNamara |first1=Kenneth J. |bibcode=2007GSLSP.273..279M |s2cid=129384807 |url-access=subscription }}</ref><ref>{{Cite web |url=http://echinoblog.blogspot.com/2009/01/archaeological-echinoderm-fairy-loaves.html |title=Archaeological Echinoderm! Fairy Loaves & Thunderstones! |access-date=16 February 2019 |archive-url=https://web.archive.org/web/20190217084856/http://echinoblog.blogspot.com/2009/01/archaeological-echinoderm-fairy-loaves.html |archive-date=17 February 2019 |url-status=dead |date=12 January 2009 }}</ref>

=== Early modern explanations ===
[[File:Anoplotherium 1812 Skeleton Sketch.jpg|thumb|Georges Cuvier's 1812 skeletal reconstruction of ''[[Anoplotherium]] commune'' based on fossil remains of the extinct [[artiodactyl]] from [[Montmartre]] in Paris, France]]
More scientific views of fossils emerged during the [[Renaissance]]. [[Leonardo da Vinci]] concurred with Aristotle's view that fossils were the remains of ancient life.<ref>{{ cite journal
| title= Leonardo da Vinci, the founding father of ichnoogy
| first = Andrea | last = Baucon
| journal = PALAIOS
| volume = 25 | number= 5/6 
| date = 2010
| pages = 361–367
| publisher = SEPM Society for Sedimentary Geology
| doi = 10.2110/palo.2009.p09-049r | jstor=40606506
| bibcode = 2010Palai..25..361B | s2cid = 86011122 }}</ref>{{rp|361}} For example, Leonardo noticed discrepancies with the biblical flood narrative as an explanation for fossil origins:

{{blockquote|If the Deluge had carried the shells for distances of three and four hundred miles from the sea it would have carried them mixed with various other natural objects all heaped up together; but even at such distances from the sea we see the oysters all together and also the shellfish and the cuttlefish and all the other shells which congregate together, found all together dead; and the solitary shells are found apart from one another as we see them every day on the sea-shores.}}

{{blockquote|And we find oysters together in very large families, among which some may be seen with their shells still joined together, indicating that they were left there by the sea and that they were still living when the strait of Gibraltar was cut through. In the mountains of Parma and Piacenza multitudes of shells and corals with holes may be seen still sticking to the rocks....<ref>{{cite book | last =da Vinci | first =Leonardo | author-link =Leonardo da Vinci | title =The Notebooks of Leonardo da Vinci | publisher =Reynal & Hitchcock | date =1956 | orig-year =1938 | location =London | page =335 | url ={{google books |plainurl=y |id=qMoQAAAAIAAJ|page335}} | isbn =978-0-9737837-3-5 }}{{Dead link|date=September 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>}}

[[File:Rozprawa o přewratech kůry zemnj, Ichthyosaurus and Plesiosaurus.jpg|thumb|upright=1.2|''[[Ichthyosaurus]]'' and ''[[Plesiosaurus]]'' from the 1834 Czech edition of [[Georges Cuvier|Cuvier]]'s ''Discours sur les revolutions de la surface du globe'']]
In 1666, [[Nicholas Steno]] examined a shark, and made the association of its teeth with the "tongue stones" of ancient Greco-Roman mythology, concluding that those were not in fact the tongues of venomous snakes, but the teeth of some long-extinct species of shark.<ref name=sharkteeth />

[[Robert Hooke]] (1635–1703) included [[micrograph]]s of fossils in his ''[[Micrographia]]'' and was among the first to observe fossil [[foram]]s. His observations on fossils, which he stated to be the petrified remains of creatures some of which no longer existed, were published posthumously in 1705.<ref>{{Cite news |url=https://blogs.scientificamerican.com/history-of-geology/july-2-1635-robert-hooke-the-last-virtuoso-of-silly-science/ |title=July 18, 1635: Robert Hooke – The Last Virtuoso of Silly Science |last=Bressan |first=David |work=Scientific American Blog Network |access-date=11 February 2018 |language=en |archive-url=https://web.archive.org/web/20180212142108/https://blogs.scientificamerican.com/history-of-geology/july-2-1635-robert-hooke-the-last-virtuoso-of-silly-science/ |archive-date=12 February 2018 |url-status=dead }}</ref>

[[William Smith (geologist)|William Smith (1769–1839)]], an English canal engineer, observed that rocks of different ages (based on the [[law of superposition]]) preserved different assemblages of fossils, and that these assemblages succeeded one another in a regular and determinable order. He observed that rocks from distant locations could be correlated based on the fossils they contained. He termed this the principle of ''faunal succession''. This principle became one of Darwin's chief pieces of evidence that biological evolution was real.

[[Georges Cuvier]] came to believe that most if not all the animal fossils he examined were remains of extinct species. This led Cuvier to become an active proponent of the geological school of thought called [[catastrophism]]. Near the end of his 1796 paper on living and fossil elephants he said:

{{blockquote|All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove the existence of a world previous to ours, destroyed by some kind of catastrophe.<ref>{{cite web|url=http://palaeo.gly.bris.ac.uk/Palaeofiles/History/cuvier.xhtml|title=Cuvier|website=palaeo.gly.bris.ac.uk|access-date=3 November 2008|archive-url=https://web.archive.org/web/20140525001629/http://palaeo.gly.bris.ac.uk/palaeofiles/history/cuvier.xhtml|archive-date=25 May 2014|url-status=dead}}</ref>}}

Interest in fossils, and geology more generally, expanded during the early nineteenth century.  In Britain, [[Mary Anning]]'s discoveries of fossils, including the first complete [[ichthyosaur]] and a complete [[plesiosaurus]] skeleton, sparked both public and scholarly interest.<ref>{{cite web |title=Mary Anning |url=http://www.lymeregismuseum.co.uk/collection/mary-anning/ |website=Lyme Regis Museum |access-date=21 August 2018 |archive-url=https://web.archive.org/web/20180822051829/http://www.lymeregismuseum.co.uk/collection/mary-anning/ |archive-date=22 August 2018 |url-status=dead }}</ref>

=== Linnaeus and Darwin ===
Early [[natural science|naturalists]] well understood the similarities and differences of living species leading [[Carl Linnaeus|Linnaeus]] to develop a hierarchical classification system still in use today. Darwin and his contemporaries first linked the hierarchical structure of the tree of life with the then very sparse fossil record. Darwin eloquently described a process of descent with modification, or evolution, whereby organisms either adapt to natural and changing environmental pressures, or they perish.

When Darwin wrote ''[[On the Origin of Species|On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life]]'', the oldest animal fossils were those from the [[Cambrian]] Period, now known to be about 540&nbsp;million years old. He worried about the absence of older fossils because of the implications on the validity of his theories, but he expressed hope that such fossils would be found, noting that: "only a small portion of the world is known with accuracy." Darwin also pondered the sudden appearance of many groups (i.e. [[phylum|phyla]]) in the oldest known Cambrian fossiliferous strata.<ref>{{Citation|last=Darwin|first=Charles|chapter=[[:s:The Origin of Species (1872)/Chapter X|Chapter X: On the Imperfection of the Geological Record]]|title=[[On the Origin of Species|The Origin of Species]]
| author-link= Charles Darwin
| year = 1872
| place= London| publisher= John Murray
}}</ref>

=== After Darwin ===
Since Darwin's time, the fossil record has been extended to between 2.3 and 3.5&nbsp;billion years.<ref>Schopf JW (1999) Cradle of Life: The Discovery of the Earth's Earliest Fossils, Princeton University Press, Princeton, NJ.</ref> Most of these Precambrian fossils are microscopic bacteria or [[micropaleontology|microfossils]]. However, macroscopic fossils are now known from the late Proterozoic. The [[Ediacara biota]] (also called Vendian biota) dating from 575&nbsp;million years ago collectively constitutes a richly diverse assembly of early multicellular [[eukaryote]]s.

The fossil record and faunal succession form the basis of the science of [[biostratigraphy]] or determining the age of rocks based on embedded fossils. For the first 150 years of [[geology]], biostratigraphy and superposition were the only means for determining the [[relative dating|relative age]] of rocks. The [[geologic time scale]] was developed based on the relative ages of rock strata as determined by the early paleontologists and [[stratigraphy|stratigraphers]].

Since the early years of the twentieth century, [[absolute dating]] methods, such as [[radiometric dating]] (including [[K–Ar dating|potassium/argon]], [[Argon–argon dating|argon/argon]], [[uranium–lead dating|uranium series]], and, for very recent fossils, [[radiocarbon dating]]) have been used to verify the relative ages obtained by fossils and to provide absolute ages for many fossils. Radiometric dating has shown that the earliest known stromatolites are over 3.4&nbsp;billion years old.

=== Modern era ===
{{Quote box
|quote = The fossil record is life's evolutionary epic that unfolded over four&nbsp;billion years as environmental conditions and genetic potential interacted in accordance with natural selection.|source = The Virtual Fossil Museum<ref>{{cite web| url=http://www.fossilmuseum.net/| title=The Virtual Fossil Museum – Fossils Across Geological Time and Evolution| access-date=4 March 2007| archive-url=https://web.archive.org/web/20070308145410/http://www.fossilmuseum.net/| archive-date=8 March 2007| url-status=live}}</ref>|width = 40%|bgcolor =}}

Paleontology has joined with [[evolutionary biology]] to share the interdisciplinary task of outlining the tree of life, which inevitably leads backwards in time to Precambrian microscopic life when cell structure and functions evolved. Earth's deep time in the Proterozoic and deeper still in the Archean is only "recounted by microscopic fossils and subtle chemical signals."<ref>Knoll, A, (2003) Life on a Young Planet. (Princeton University Press, Princeton, NJ)</ref> Molecular biologists, using [[phylogenetics]], can compare protein [[amino acid]] or [[nucleotide]] sequence homology (i.e., similarity) to evaluate taxonomy and evolutionary distances among organisms, with limited statistical confidence. The study of fossils, on the other hand, can more specifically pinpoint when and in what organism a mutation first appeared. Phylogenetics and paleontology work together in the clarification of science's still dim view of the appearance of life and its evolution.<ref>{{cite book |editor=Donovan, S. K.|editor2=Paul, C. R. C.|date= 1998 |chapter=An Overview of the Completeness of the Fossil Record |title=The Adequacy of the Fossil Record |pages=111–131 |publisher=Wiley |location= New York |isbn=978-0-471-96988-4}}</ref>

[[File:Eldredgeops-rana-crassituberculata.jpg|thumb|[[Phacopid]] [[trilobite]] ''Eldredgeops rana crassituberculata''. The genus is named after [[Niles Eldredge]]]]

[[Niles Eldredge]]'s study of the ''[[Phacops]]'' [[trilobite]] genus supported the hypothesis that modifications to the arrangement of the trilobite's eye lenses proceeded by fits and starts over millions of years during the [[Devonian]].<ref>[[Fortey, Richard]], ''Trilobite!: Eyewitness to Evolution''. Alfred A. Knopf, New York, 2000.</ref> Eldredge's interpretation of the ''Phacops'' fossil record was that the aftermaths of the lens changes, but not the rapidly occurring evolutionary process, were fossilized. This and other data led [[Stephen Jay Gould]] and Niles Eldredge to publish their seminal paper on [[punctuated equilibrium]] in 1971.

[[Synchrotron]] [[X-ray]] [[Tomography|tomographic]] analysis of early Cambrian bilaterian [[embryo]]nic microfossils yielded new insights of [[Animal|metazoan]] evolution at its earliest stages. The tomography technique provides previously unattainable three-dimensional resolution at the limits of fossilization. Fossils of two enigmatic bilaterians, the worm-like ''[[Markuelia]]'' and a putative, primitive [[protostome]], ''[[Pseudooides]]'', provide a peek at [[germ layer]] embryonic development. These 543-million-year-old embryos support the emergence of some aspects of [[arthropod]] development earlier than previously thought in the late Proterozoic. The preserved embryos from [[China]] and [[Siberia]] underwent rapid [[Diagenesis|diagenetic]] phosphatization resulting in exquisite preservation, including cell structures.{{Technical inline|date=May 2021}} This research is a notable example of how knowledge encoded by the fossil record continues to contribute otherwise unattainable information on the emergence and development of life on Earth. For example, the research suggests ''Markuelia'' has closest affinity to priapulid worms, and is adjacent to the evolutionary branching of [[Priapulida]], [[Nematode|Nematoda]] and [[Arthropod]]a.<ref>{{cite journal | last1 = Donoghue | first1 = PCJ | last2 = Bengtson | first2 = S | last3 = Dong | first3 = X | last4 = Gostling | first4 = NJ | last5 = Huldtgren | first5 = T | last6 = Cunningham | first6 = JA | last7 = Yin | first7 = C | last8 = Yue | first8 = Z | last9 = Peng | first9 = F | year = 2006 | title = Synchrotron X-ray tomographic microscopy of fossil embryos | journal = Nature | volume = 442 | issue = 7103| pages = 680–683 | doi=10.1038/nature04890| pmid = 16900198 |display-authors= etal | bibcode = 2006Natur.442..680D | s2cid = 4411929 }}</ref>{{Technical inline|date=May 2021}}

Despite significant advances in uncovering and identifying paleontological specimens, it is generally accepted that the fossil record is vastly incomplete.<ref name="foote1999">{{cite journal | last1 = Foote | first1 = M. | last2 = Sepkoski | first2 = J.J. Jr | title = Absolute measures of the completeness of the fossil record | date = 1999 | journal = Nature | volume = 398 | issue = 6726 | pages = 415–417 | doi = 10.1038/18872| pmid = 11536900 | bibcode = 1999Natur.398..415F | s2cid = 4323702 }}</ref><ref name="benton2009">{{cite journal | last = Benton | first = M. | date = 2009 | title = The completeness of the fossil record | journal = Significance | volume = 6 | issue = 3 | pages = 117–121 | doi = 10.1111/j.1740-9713.2009.00374.x| s2cid = 84441170 | doi-access = free }}</ref> Approaches for measuring the completeness of the fossil record have been developed for numerous subsets of species, including those grouped taxonomically,<ref name="zliobaite2021">{{cite journal | last1 = Žliobaitė | first1 = I. | last2 = Fortelius | first2 = M. | date = 2021 | title = On calibrating the completometer for the mammalian fossil record | journal = Paleobiology | volume = 48 | pages = 1–11 | doi = 10.1017/pab.2021.22| s2cid = 238686414 | doi-access = free }}</ref><ref name="eiting2009">{{cite journal | last1 = Eiting | first1 = T.P. | last2 = Gunnell | first2 = G.G | title = Global Completeness of the Bat Fossil Record | journal = Journal of Mammalian Evolution | date = 2009 | volume = 16 | issue = 3 | pages = 151–173 | doi = 10.1007/s10914-009-9118-x| s2cid = 5923450 }}</ref> temporally,<ref name="brocklehurst2012">{{cite journal | title = The Completeness of the Fossil Record of Mesozoic Birds: Implications for Early Avian Evolution | last1 = Brocklehurst | first1 = N. | last2 = Upchurch | first2 = P. | last3 = Mannion | first3 = P.D. | last4 = O'Connor | first4 = J. | journal = PLOS ONE| date = 2012 | volume = 7 | issue = 6 | page = e39056 | doi = 10.1371/journal.pone.0039056| pmid = 22761723 | pmc = 3382576 | bibcode = 2012PLoSO...739056B | doi-access = free }}</ref> environmentally/geographically,<ref name="retallack1984">{{cite journal | title = Completeness of the rock and fossil record: some estimates using fossil soils | last = Retallack | first = G. | journal = Paleobiology | volume = 10 | issue = 1 | date = 1984 | pages = 59–78 | doi = 10.1017/S0094837300008022| bibcode = 1984Pbio...10...59R | s2cid = 140168970 }}</ref> or in sum.<ref name="benton1994">{{cite journal | last1 = Benton | first1 = M.J. | last2 = Storrs | first2 = G.Wm. | title = Testing the quality of the fossil record: Paleontological knowledge is improving | journal = Geology | date = 1994 | volume = 22 | number = 2 | pages = 111–114 | doi = 10.1130/0091-7613(1994)022<0111:TTQOTF>2.3.CO;2| bibcode = 1994Geo....22..111B }}</ref><ref name="holland1999">{{cite journal | last1 = Holland | first1 = S.M. | last2 = Patzkowsky | first2 = M.E. | date = 1999 | volume = 27 | number = 6 | pages = 491–494 | doi = 10.1130/0091-7613(1999)027<0491:MFSTFR>2.3.CO;2 | title = Models for simulating the fossil record| journal = Geology | bibcode = 1999Geo....27..491H }}</ref> This encompasses the subfield of [[taphonomy]] and the study of biases in the paleontological record.<ref name="koch1978">{{cite journal | last = Koch | first = C. | title = Bias in the published fossil record | journal = Paleobiology | volume = 4 | number = 3 | pages = 367–372 | doi = 10.1017/S0094837300006060 | date = 1978| bibcode = 1978Pbio....4..367K | s2cid = 87368101 }}</ref><ref name="signor1982">{{cite book | last1 = Signore | first1 = P.W. III | last2 = Lipps | first2 = J.H. | chapter = Sampling bias, gradual extinction patterns and catastrophes in the fossil record | title = Geological Implications of Impacts of Large Asteroids and Comets on the Earth | series = Geological Society of America Special Papers | year = 1982 | volume = 190 | editor-last1 = Silver | editor-first1 = L.T. | editor-last2 = Schultz | editor-first2 = P.H. | pages = 291–296 | doi = 10.1130/SPE190-p291| isbn = 0-8137-2190-3 }}</ref><ref name="vilhena2013">{{cite journal | last1 = Vilhena | first1 = D.A. | last2 = Smith | first2 = A.B. | title = Spatial Bias in the Marine Fossil Record | journal = PLOS ONE| volume = 8 | number = 10 | page = e74470 | doi = 10.1371/journal.pone.0074470 | date = 2013| pmid = 24204570 | pmc = 3813679 | bibcode = 2013PLoSO...874470V | doi-access = free }}</ref>

== Dating/Age ==

=== Stratigraphy and estimations ===
{{Main|Geochronology|Relative dating}}
[[File:Montañita-Olón locality (stratigraphy) - Dos Bocas Formation.png|thumb|Stratigraphy of the Montañita-Olón locality of the [[Dos Bocas Formation]]. Stratigraphy is a useful branch when it comes to the understanding of the successive layers of rock and their fossiliferous content, giving insight into the relative age of fossils]]
Paleontology seeks to map out how life evolved across geologic time. A substantial hurdle is the difficulty of working out fossil ages. Beds that preserve fossils typically lack the radioactive elements needed for [[radiometric dating]]. This technique is our only means of giving rocks greater than about 50&nbsp;million years old an absolute age, and can be accurate to within 0.5% or better.<ref name="Martin2000">{{Cite journal | author1 = Martin, M.W. | author2 = Grazhdankin, D.V. |author3=Bowring, S.A. |author4=Evans, D.A.D. |author5=Fedonkin, M.A. |author6=Kirschvink, J.L. | s2cid = 1019572 | date = 5 May 2000 | title = Age of Neoproterozoic Bilaterian Body and Trace Fossils, White Sea, Russia: Implications for Metazoan Evolution | journal = Science | volume = 288 | issue = 5467 | pages = 841–5 | doi = 10.1126/science.288.5467.841 | pmid = 10797002 |bibcode = 2000Sci...288..841M}}</ref> Although radiometric dating requires careful laboratory work, its basic principle is simple: the rates at which various radioactive elements [[radioactive decay|decay]] are known, and so the ratio of the radioactive element to its decay products shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers, which may provide termini for the intervening sediments.<ref name="Martin2000" />

Consequently, palaeontologists rely on [[stratigraphy]] to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the [[sediment]]ary record.<ref>{{Cite journal |author1=Pufahl, P.K. |author2=Grimm, K.A. |author3=Abed, A.M. |author4=Sadaqah, R.M.Y. |name-list-style=amp | title=Upper Cretaceous (Campanian) phosphorites in Jordan: implications for the formation of a south Tethyan phosphorite giant | journal=[[Sedimentary Geology (journal)|Sedimentary Geology]] | volume=161 |date=October 2003 | pages=175–205 | doi=10.1016/S0037-0738(03)00070-8 | issue=3–4 | bibcode=2003SedG..161..175P}}</ref> Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age is claimed to lie between the two known ages.<ref>{{cite web | url=http://pubs.usgs.gov/gip/geotime/radiometric.html | access-date=20 September 2008 | title=Geologic Time: Radiometric Time Scale | publisher=U.S. Geological Survey | archive-url=https://web.archive.org/web/20080921135337/http://pubs.usgs.gov/gip/geotime/radiometric.html | archive-date=21 September 2008 | url-status=live }}</ref> Because rock sequences are not continuous, but may be broken up by [[fault (geology)|faults]] or periods of [[erosion]], it is very difficult to match up rock beds that are not directly adjacent. However, fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called ''biostratigraphy''. For instance, the conodont ''Eoplacognathus pseudoplanus'' has a short range in the Middle Ordovician period.<ref>{{Cite journal | author = Löfgren, A. | year = 2004 | title = The conodont fauna in the Middle Ordovician ''Eoplacognathus pseudoplanus'' Zone of Baltoscandia | journal = Geological Magazine | volume = 141 | issue = 4 | pages = 505–524
| doi = 10.1017/S0016756804009227 | doi-broken-date = 21 January 2025 | bibcode = 2004GeoM..141..505L | s2cid = 129600604 }}</ref> If rocks of unknown age have traces of ''E. pseudoplanus'', they have a mid-Ordovician age. Such [[index fossil]]s must be distinctive, be globally distributed and occupy a short time range to be useful. Misleading results are produced if the index fossils are incorrectly dated.<ref name=Gehling2001>{{Cite journal | last1 = Gehling | first1 = James | last2 = Jensen | first2 = Sören | last3 = Droser | first3 = Mary | last4 = Myrow | first4 = Paul | last5 = Narbonne | first5 = Guy | title = Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland | journal = Geological Magazine | volume = 138 | issue = 2 | pages = 213–218 | date = March 2001 | doi = 10.1017/S001675680100509X | bibcode = 2001GeoM..138..213G | s2cid = 131211543 }}</ref> Stratigraphy and biostratigraphy can in general provide only relative dating (''A'' was before ''B''), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching rocks of the same age across [[continent]]s.<ref name="Gehling2001" /> Family-tree relationships also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X&nbsp;million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved earlier.

It is also possible to estimate how long ago two living clades diverged (i.e., the age of their [[last common ancestor]]) by assuming that [[mutation]]s accumulate at a constant rate for a given gene. These "[[molecular clock]]s", however, are fallible, and provide only approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the [[Cambrian explosion]] first evolved,<ref>{{Cite journal |author1=Hug, L.A. |author2=Roger, A.J. | title=The Impact of Fossils and Taxon Sampling on Ancient Molecular Dating Analyses | journal=Molecular Biology and Evolution | year=2007 | volume=24 | issue=8 | pages=889–1897 | doi=10.1093/molbev/msm115 | pmid=17556757| doi-access=free }}</ref> and estimates produced by different techniques may vary by a factor of two.<ref name="PetersonEtAl2005">{{Cite journal | doi = 10.1073/pnas.0503660102 | pmid = 15983372 |author1=Peterson, Kevin J. |author2=Butterfield, N.J. | journal = Proceedings of the National Academy of Sciences | volume = 102 | issue = 27 | pages = 9547–52 | year = 2005
| title = Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record | pmc = 1172262 |bibcode=2005PNAS..102.9547P| doi-access = free }}</ref>

=== Limitations <span class="anchor" id="Fossil record limitations"></span>===
<!-- use anchor because other articles link to this section, and a change to its name recently broke such a link -->
{{Further|Ghost lineage|Signor–Lipps effect|Biostratigraphy}}

Organisms are only rarely preserved as fossils in the best of circumstances, and only a fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived.<ref name=Prothero2007pp5053>{{cite book |author-link=Donald Prothero |last=Prothero |first=Donald R. |date=2007 |title=Evolution: What the Fossils Say and Why It Matters |url=https://archive.org/details/evolutionwhatfos00prot_0/page/50 |url-access=registration |pages=[https://archive.org/details/evolutionwhatfos00prot_0/page/50 50–53] |publisher=[[Columbia University Press]] |isbn=978-0-231-51142-1 }}</ref> Because of the specialized and rare circumstances required for a biological structure to fossilize, only a small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which are never guaranteed to demonstrate a convenient half-way point.<ref name="CC200">{{cite web|url = http://www.talkorigins.org/indexcc/CC/CC200.html|title = Claim CC200: There are no transitional fossils.|access-date = 30 April 2009|date = 5 November 2006|publisher = [[TalkOrigins Archive]]|last = Isaak|first = M|archive-url = https://web.archive.org/web/20090227065512/http://www.talkorigins.org/indexcc/CC/CC200.html|archive-date = 27 February 2009|url-status = live}}</ref>

The fossil record is strongly biased toward organisms with hard parts, leaving most groups of [[soft-bodied organism]]s with little to no presence.<ref name=Prothero2007pp5053 /> It is replete with [[Mollusca|mollusks]], [[vertebrate]]s, [[echinoderm]]s, [[brachiopod]]s, and some groups of [[arthropod]]s.<ref>{{cite book|editor=Donovan, S. K.|editor2=Paul, C. R. C. |date= 1998 |title= The Adequacy of the Fossil Record |publisher=Wiley |location= New York |page= 312 |isbn=978-0-471-96988-4}}{{page needed|date=August 2014}}</ref>

== Sites ==
=== Lagerstätten ===
{{Main|Lagerstätte}}
{{Further|List of fossil sites}}

Fossil sites with exceptional preservation—sometimes including preserved soft tissues—are known as [[Lagerstätte]]n (German for "storage places"). These formations may have resulted from carcass burial in an [[hypoxia (environmental)|anoxic]] environment with minimal bacteria, thus slowing decomposition. Lagerstätten span geological time from the [[Cambrian]] period to the [[Holocene|present]]. Worldwide, some of the best examples of near-perfect fossilization are the [[Cambrian]] [[Maotianshan Shales]] and [[Burgess Shale]], the [[Devonian]] [[Hunsrück Slate]]s, the [[Jurassic]] [[Solnhofen Limestone]], and the [[Carboniferous]] [[Mazon Creek]] localities.

== Fossilization processes ==
=== Recrystallization ===
A fossil is said to be ''recrystallized'' when the original skeletal compounds are still present but in a different crystal form, such as from [[aragonite]] to [[calcite]].{{sfn|Prothero|2013|pp=8-9}}
<gallery widths="150" heights="200">
File:Calcite-60801.jpg|[[Calcite]]-recrystallized fossil shell of ''[[Mercenaria permagna]]'' from [[Fort Drum, Florida]]
File:Geodized fossil Busycon snail with yellowish calcite crystals (Anastasia Formation, Upper Pleistocene to lower Holocene, 126 to 8 ka; Indrio Pit, northern side of the town of Fort Pierce, southeastern Florida, USA) (15227151971).jpg|Calcite-recrystallized fossil shell of ''[[Busycon]]'' sp. from Indrio Pit
File:MatmorScleractinian.JPG|Recrystallized [[scleractinia]]n coral (aragonite to calcite) from the [[Jurassic]] of southern [[Israel]]
File:Geodized pentamerid brachiopods (Silurian; Swayzee, Indiana, USA) 1.jpg|Calcite-recrystallized fossil shell of [[pentamerid]] [[brachiopods]] from [[Indiana]]
File:GeopetalCarboniferousNV.jpg|Recrystallized bivalve shell with sparry calcite from [[Bird Spring Formation]]
</gallery>

=== Replacement ===
[[File:Permineralized bryozoan.jpg|thumb|Permineralized [[bryozoan]] from the [[Devonian]] of Wisconsin]]
Replacement occurs when the shell, bone, or other tissue is replaced with another mineral. In some cases mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material. Scientists can use such fossils when researching the anatomical structure of ancient species.<ref>{{Cite web|title=Molecular Expressions Microscopy Primer: Specialized Microscopy Techniques - Phase Contrast Photomicrography Gallery - Agatized Dinosaur Bone|url=https://micro.magnet.fsu.edu/primer/techniques/phasegallery/agatizeddinobone.html|access-date=2021-02-12|website=micro.magnet.fsu.edu}}</ref> Several species of saurids have been identified from mineralized dinosaur fossils.<ref name=natgeo>{{Cite web|date=2018-12-04|title=Exclusive: Sparkly, opal-filled fossils reveal new dinosaur species|url=https://www.nationalgeographic.com/science/2018/12/exclusive-sparkly-opal-filled-fossils-reveal-new-dinosaur-species-paleontology/|archive-url=https://web.archive.org/web/20181204142402/https://www.nationalgeographic.com/science/2018/12/exclusive-sparkly-opal-filled-fossils-reveal-new-dinosaur-species-paleontology/|url-status=dead|archive-date=December 4, 2018|access-date=2021-02-12|website=Science|language=en}}</ref><ref>{{Cite web|date=2019-06-03|title=Gem-like fossils reveal stunning new dinosaur species|url=https://www.nationalgeographic.com/science/2019/06/opal-fossils-reveal-new-species-dinosaur-australia-fostoria/|archive-url=https://web.archive.org/web/20190604033106/https://www.nationalgeographic.com/science/2019/06/opal-fossils-reveal-new-species-dinosaur-australia-fostoria/|url-status=dead|archive-date=June 4, 2019|access-date=2021-02-12|website=Science|language=en}}</ref>

==== Permineralization ====
[[Permineralization]] is a process of fossilization that occurs when an organism is buried. The empty spaces within an organism (spaces filled with liquid or gas during life) become filled with mineral-rich [[groundwater]]. Minerals precipitate from the groundwater, occupying the empty spaces. This process can occur in very small spaces, such as within the [[cell wall]] of a [[plant cell]], and can produce very detailed fossils at small scales.<ref>{{cite book |last1=Prothero |first1=Donald R. |title=Bringing fossils to life : an introduction to paleobiology |date=2013 |publisher=Columbia University Press |location=New York |isbn=978-0-231-15893-0 |page=8 |edition=Third}}</ref> For permineralization to occur, the organism must become covered by sediment soon after death, otherwise the remains are destroyed by scavengers or decomposition.{{sfn|Prothero|2013|pp=12-13}} The degree to which the remains are decayed when covered determines the later details of the fossil. Some fossils consist only of skeletal remains or teeth; other fossils contain traces of [[skin]], [[feather]]s or even soft tissues.{{sfn|Prothero|2013|p=16}} This is a form of [[diagenesis]].

====Phosphatization====
Phosphatization refers to a process of fossilization where organic matter is replaced by abundant [[calcium]]-[[phosphate]] [[mineral]]s. The produced fossils tend to be particularly dense and have a dark coloration that ranges from dark orange to black.<ref>{{Cite journal | doi = 10.1016/S0016-6995(97)80056-3 | last1 = Wilby | first1 = P. | last2 = Briggs | first2 = D. | title = Taxonomic trends in the resolution of detail preserved in fossil phosphatized soft tissues | journal = Geobios | volume = 30 | pages = 493–502 | year = 1997| bibcode = 1997Geobi..30..493W }}</ref>

====Pyritization====
This fossil preservation involves the elements [[sulfur]] and [[iron]]. Organisms may become pyritized when they are in marine sediments saturated with iron sulfides. As organic matter decays, it releases sulfide which reacts with dissolved iron in the surrounding waters, forming [[pyrite]]. Pyrite replaces carbonate shell material due to an undersaturation of carbonate in the surrounding waters.  Some plants become pyritized when they are in a clay terrain, but to a lesser extent than in a marine environment. Some pyritized fossils include [[Precambrian]] microfossils, marine [[arthropods]], and plants.<ref>Wacey, D. et al (2013) Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the ~1.9-Ga Gunflint chert ''PNAS'' 110 (20) 8020-8024 {{doi| 10.1073/pnas.1221965110}}
</ref><ref>Raiswell, R. (1997). A geochemical framework for the application of stable sulfur isotopes to fossil pyritization. ''Journal of the Geological Society'' 154, 343–356.
</ref>
<gallery widths="150" heights="200">
File:Pleuroceras solare, Little Switzerland, Bavaria, Germany.jpg|Pyritized ammonoid ''[[Pleuroceras solare]]'' fossil specimen
File:Paraspirifer bownockeri.fond.jpg|Pyritized specimen of the brachiopod ''[[Paraspirifer bownockeri]]''
File:Triarthrus eatoni (pyritized fossil trilobite with appendages) (Whetstone Gulf Formation, Upper Ordovician; Lewis County, New York State, USA) 3.jpg|Pyritized ''[[Triarthrus eatoni]]'' from [[Whetstone Gulf Formation]]
File:Furcaster paleozoicus fossil brittle star (Kaub Formation, Hunsrück Slate Group, Lower Devonian; Budenbach area, western Germany) 4 (15302668235).jpg|Pyritized ''[[Furcaster paleozoicus]]'' from [[Hunsrück Slate]]
File:Tornoceras uniangulare aldenense fossil goniatite (Alden Pyrite Bed, Ludlowville Formation, Middle Devonian; western New York State, USA) 1 (15359943429).jpg|Pyritized ''[[Tornoceras uniangulare]]'' from [[Ludlowville Formation]]
</gallery>

====Silicification====
In [[silicification]], the precipitation of [[silica]] from saturated water bodies is responsible for the fossil's formation and preservation. The mineral-laden water permeates the pores and cells of some dead organism, where it becomes a [[gel]].  Over time, the gel will [[drying| dehydrate]], forming a [[silica]]-rich crystal structure, which can be expressed in the form of [[quartz]], [[chalcedony]], [[agate]], [[opal]], among others, with the shape of the original remain.<ref>Oehler, John H., & Schopf, J. William (1971). Artificial microfossils: Experimental studies of permineralization of blue-green algae in silica. ''Science''. 174, 1229–1231.</ref><ref>{{Cite journal |last1=Götz |first1=Annette E. |last2=Montenari |first2=Michael |last3=Costin |first3=Gelu |date=2017 |title=Silicification and organic matter preservation in the Anisian Muschelkalk: Implications for the basin dynamics of the central European Muschelkalk Sea |journal=Central European Geology |volume=60 |issue=1 |pages=35–52 |doi=10.1556/24.60.2017.002 |bibcode=2017CEJGl..60...35G |issn=1788-2281 |doi-access=free}}</ref>
<gallery widths="150" heights="200">
File:2017-07-15 22-10-35 (C) DxO.jpg|Chalcedony replaced fossil shells of ''[[Elimia tenera]]'' with inclusions of [[ostracods]]
File:Chalcedonized fossil gastropods (Cretaceous; possibly from Dakhla, southern Morocco) (15230327942).jpg|Chalcedonized [[gastropods]] internal molds
File:Schnecken auflicht small.jpg|Agatized internal molds of gastropods from [[Deccan Traps]]
File:Agate Chalcedony GE9323 540424.jpg|Agatized fossil coral from [[Florida]]
File:Opaleautralie.jpg|Fossil bivalves replaced by [[opal]], from [[Queensland]]
File:Addyman 3.JPG|Rear view of an opalized Addyman [[Plesiosauria|Plesiosaur]] fossil at the [[South Australian Museum]]
</gallery>

=== Casts and molds ===
{{anchor|Cast}} <!--[[Cast (geology)]] and [[Casting (geology)]] redirect here-->
In some cases, the original remains of the organism completely dissolve or are otherwise destroyed. The remaining organism-shaped hole in the rock is called an ''external mold''. If this void is later filled with sediment, the resulting ''cast'' resembles what the organism looked like. An [[endocast]], or ''internal mold'', is the result of sediments filling an organism's interior, such as the inside of a [[bivalve]] or [[snail]] or the hollow of a [[skull]].{{sfn|Prothero|2013|pp=9-10}} Endocasts are sometimes termed {{lang|de|Steinkerns}}, especially when bivalves are preserved this way.<ref>{{cite web |url=https://www.merriam-webster.com/dictionary/steinkern |title=Definition of Steinkern |website=Merriam-Webster |access-date=13 May 2021 |quote=a fossil consisting of a stony mass that entered a hollow natural object (such as a bivalve shell) in the form of mud or sediment, was consolidated, and remained as a cast after dissolution of the mold |archive-date=13 May 2021 |archive-url=https://web.archive.org/web/20210513191727/https://www.merriam-webster.com/dictionary/steinkern |url-status=live }}</ref>
<gallery widths="150" heights="200">
File:Internal mold, Hormotoma, Mollusca, Gastropoda, Murchisonioidea - Iowa, USA.jpg|Internal mold (steinkern) of ''[[Hormotoma]]'' sp. from [[Galena Formation]]
File:Small-gasteropod-bariloche.jpg|Gastropod internal mold (steinkern) from [[Ventana Formation]]
File:Anomalodonta gigantea Waynesville Franklin Co IN.JPG|Shell external mold of ''[[Anomalodonta gigantea]]'' from [[Waynesville Formation]]
File:Glycymeris alpinus 01.jpg|Internal mold (steinkern) of ''[[Glycymeris alpinus]]'', [[Austria]]
File:Aviculopecten subcardiformis01.JPG|External mold of ''[[Aviculopecten subcardiformis]]'' from the [[Logan Formation]], Lower [[Carboniferous]], Ohio
</gallery>

==== Authigenic mineralization ====
This is a special form of cast and mold formation. If the chemistry is right, the organism (or fragment of organism) can act as a nucleus for the precipitation of minerals such as [[siderite]], resulting in a nodule forming around it. If this happens rapidly before significant decay to the organic tissue, very fine three-dimensional morphological detail can be preserved. Nodules from the Carboniferous [[Mazon Creek fossil beds]] of Illinois, US, are among the best documented examples of such mineralization.{{sfn|Prothero|2013|p=579}}

=== Adpression (compression-impression) ===
[[Compression fossil]]s, such as those of fossil ferns, are the result of chemical reduction of the complex organic molecules composing the organism's tissues. In this case, the fossil consists of original material, albeit in a geochemically altered state. This chemical change is an example of [[diagenesis]]. What remains is often a [[carbonaceous film]] known as a phytoleim, in which case the fossil is known as a compression. Often, however, the phytoleim is lost and all that remains is an impression of the organism in the rock—an impression fossil. In many cases, however, compressions and impressions occur together. For instance, when the rock is broken open, the phytoleim will often be attached to one part (compression), whereas the counterpart will just be an impression. For this reason, one term covers the two modes of preservation: ''adpression''.<ref name="ShuteCleal 1986">{{cite journal|last1=Shute |first1=C. H. |last2=Cleal |first2=C. J. |year=1986 |journal=Geological Curator |volume=4 |title=Palaeobotany in museums |issue=9 |pages=553–559|doi=10.55468/GC865 |s2cid=251638416 |doi-access=free }}</ref>

==== Carbonization and coalification ====
Fossils that are carbonized or coalified consist of the organic remains which have been reduced primarily to the chemical element carbon. Carbonized fossils consist of a thin film which forms a silhouette of the original organism, and the original organic remains were typically soft tissues. Coalified fossils consist primarily of coal, and the original organic remains were typically woody in composition.

<gallery widths="150" heights="200">
File:Probable leech from the Waukesha Biota.jpg|Carbonized fossil of a [[cycloneuralia]]n worm that was once misidentified as a [[leech]]<ref>{{Cite journal |last1=Braddy |first1=Simon J. |last2=Gass |first2=Kenneth C. |last3=Tessler |first3=Michael |date=2023-09-04 |title=Not the first leech: An unusual worm from the early Silurian of Wisconsin |url=https://www.cambridge.org/core/journals/journal-of-paleontology/article/not-the-first-leech-an-unusual-worm-from-the-early-silurian-of-wisconsin/2AB9EDAF214C38A8EE93C260BAC9878D |journal=Journal of Paleontology |volume=97 |issue=4 |language=en |pages=799–804 |doi=10.1017/jpa.2023.47 |bibcode=2023JPal...97..799B |s2cid=261535626 |issn=0022-3360}}</ref> from the Silurian [[Waukesha Biota]] of Wisconsin.
File:Lycopod axis.jpg|Partially coalified axis (branch) of a [[lycopod]] from the Devonian of [[Wisconsin]].
</gallery>

=== Soft tissue, cell and molecular preservation ===
Because of their antiquity, an unexpected exception to the alteration of an organism's tissues by chemical reduction of the complex organic molecules during fossilization has been the discovery of soft tissue in dinosaur fossils, including blood vessels, and the isolation of proteins and evidence for DNA fragments.<ref name=Smith>{{cite journal |url= http://www.smithsonianmag.com/science-nature/dinosaur-shocker-115306469/?no-ist |author=Fields H |title=Dinosaur Shocker – Probing a 68-million-year-old T. rex, Mary Schweitzer stumbled upon astonishing signs of life that may radically change our view of the ancient beasts |journal=Smithsonian Magazine |date= May 2006 |archive-url= https://web.archive.org/web/20150118153415/http://www.smithsonianmag.com/science-nature/dinosaur-shocker-115306469/?no-ist |url-status=live |archive-date= 18 January 2015}}</ref><ref name=MHS1>{{cite journal |vauthors=Schweitzer MH, Wittmeyer JL, Horner JR, Toporski JK |title= Soft-tissue vessels and cellular preservation in Tyrannosaurus rex |journal= Science |volume=307 |issue=5717 |pages=1952–5 |date= 25 March 2005 |pmid=15790853 |doi= 10.1126/science.1108397 |bibcode=2005Sci...307.1952S |s2cid= 30456613 }}</ref><ref name=MHS2>{{cite journal |vauthors=Schweitzer MH, Zheng W, Cleland TP, Bern M |title=Molecular analyses of dinosaur osteocytes support the presence of endogenous molecules |journal=Bone |volume=52 |issue=1 |pages=414–23 |date=January 2013 |pmid=23085295 |doi= 10.1016/j.bone.2012.10.010}}</ref><ref name=Emb>{{cite journal | url= https://www.researchgate.net/publication/10586201 |vauthors=Embery G, Milner AC, Waddington RJ, Hall RC, Langley ML, Milan AM |title=Identification of Proteinaceous Material in the Bone of the Dinosaur Iguanodon |journal=Connective Tissue Research |volume=44 |pages=41–6 |date=2003 |pmid=12952172 | doi= 10.1080/03008200390152070 |issue=Suppl 1|s2cid=2249126 }}</ref> In 2014, [[Mary Higby Schweitzer|Mary Schweitzer]] and her colleagues reported the presence of iron particles ([[goethite]]-aFeO(OH)) associated with soft tissues recovered from dinosaur fossils. Based on various experiments that studied the interaction of iron in [[haemoglobin]] with blood vessel tissue they proposed that solution hypoxia coupled with iron [[chelation]] enhances the stability and preservation of soft tissue and provides the basis for an explanation for the unforeseen preservation of fossil soft tissues.<ref name= SchweitzerOthers2014a>{{cite journal |vauthors=Schweitzer MH, Zheng W, Cleland TP, Goodwin MB, Boatman E, Theil E, Marcus MA, Fakra SC | title= A role for iron and oxygen chemistry in preserving soft tissues, cells and molecules from deep time |journal= Proceedings of the Royal Society | volume= 281 |issue= 1774 |date= Nov 2013 |pmid= 24285202 |pmc= 3866414 | doi= 10.1098/rspb.2013.2741 | page=20132741}}</ref> However, a slightly older study based on eight [[taxa]] ranging in time from the [[Devonian]] to the [[Jurassic]] found that reasonably well-preserved fibrils that probably represent [[collagen]] were preserved in all these fossils and that the quality of preservation depended mostly on the arrangement of the collagen fibers, with tight packing favoring good preservation.<ref name=ZL11>{{cite journal| last1=Zylberberg |first1=L. | last2=Laurin|first2=M.|year=2011 |title=Analysis of fossil bone organic matrix by transmission electron microscopy |journal=Comptes Rendus Palevol |volume=11 |issue=5–6 |pages=357–366 | doi = 10.1016/j.crpv.2011.04.004}}</ref> There seemed to be no correlation between geological age and quality of preservation, within that timeframe.

=== Bioimmuration ===
[[File:Catellocaula.jpg|thumb|The star-shaped holes (''Catellocaula vallata'') in this Upper Ordovician bryozoan represent a soft-bodied organism preserved by bioimmuration in the bryozoan skeleton.<ref>{{cite journal | last1 = Palmer | first1 = T. J. | last2 = Wilson | first2 = MA | year = 1988 | title = Parasitism of Ordovician bryozoans and the origin of pseudoborings | journal = Palaeontology | volume = 31 | pages = 939–949 }}</ref>]]

Bioimmuration occurs when a skeletal organism overgrows or otherwise subsumes another organism, preserving the latter, or an impression of it, within the skeleton.<ref name="Taylor, PD. 1990">{{cite journal | last1 = Taylor | first1 = P. D. | year = 1990 | title = Preservation of soft-bodied and other organisms by bioimmuration: A review | journal = Palaeontology | volume = 33 | pages = 1–17 }}</ref> Usually it is a [[Sessility (zoology)|sessile]] skeletal organism, such as a [[bryozoan]] or an [[oyster]], which grows along a [[Substrate (biology)|substrate]], covering other sessile [[sclerobiont]]s. Sometimes the bioimmured organism is soft-bodied and is then preserved in negative relief as a kind of external mold. There are also cases where an organism settles on top of a living skeletal organism that grows upwards, preserving the settler in its skeleton. Bioimmuration is known in the fossil record from the [[Ordovician]]<ref>{{cite journal | last1 = Wilson | first1 = MA | last2 = Palmer | first2 = T. J. | last3 = Taylor | first3 = P. D. | year = 1994 | title = Earliest preservation of soft-bodied fossils by epibiont bioimmuration: Upper Ordovician of Kentucky | journal = Lethaia | volume = 27 | issue = 3| pages = 269–270 | doi=10.1111/j.1502-3931.1994.tb01420.x| bibcode = 1994Letha..27..269W }}</ref> to the Recent.<ref name="Taylor, PD. 1990" />

== 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}}

== Stromatolites ==
{{Main|Stromatolite}}
{{Further|Earliest known life forms}}
[[File:Stromatolites Cochabamba.jpg|thumb|right| Lower Proterozoic [[stromatolite]]s from [[Bolivia]], South America]]

Stromatolites are layered [[Accretion (geology)|accretionary]] [[structure]]s formed in shallow water by the trapping, binding and cementation of sedimentary grains by [[biofilm]]s of [[microorganism]]s, especially [[cyanobacteria]].<ref>{{cite journal| last = Riding | year = 2007 | first = R. | title = The term stromatolite: towards an essential definition | journal = Lethaia | volume = 32 | issue = 4 | pages = 321–330 | url = http://www3.interscience.wiley.com/journal/119935443/abstract | archive-url = https://archive.today/20150502101712/http://www3.interscience.wiley.com/journal/119935443/abstract | url-status=dead | archive-date = 2 May 2015 | doi = 10.1111/j.1502-3931.1999.tb00550.x| url-access = subscription }}</ref> Stromatolites provide some of the most ancient fossil records of life on Earth, dating back more than 3.5&nbsp;billion years ago.<ref>{{cite web| url=http://www.fossilmuseum.net/Tree_of_Life/Stromatolites.htm| title=Stromatolites, the Oldest Fossils| access-date=4 March 2007| archive-url=https://web.archive.org/web/20070309173949/http://www.fossilmuseum.net/Tree_of_Life/Stromatolites.htm| archive-date=9 March 2007| url-status=live}}</ref>

Stromatolites were much more abundant in Precambrian times. While older, [[Archean]] fossil remains are presumed to be [[colony (biology)|colonies]] of [[cyanobacteria]], younger (that is, [[Proterozoic]]) fossils may be [[prehistoric|primordial]] forms of the [[Eukaryota|eukaryote]] [[Chlorophyta|chlorophytes]] (that is, [[green algae]]). One [[genus]] of stromatolite very common in the [[geologic time scale|geologic record]] is ''[[Collenia]]''. The earliest stromatolite of confirmed microbial origin dates to 2.724&nbsp;billion years ago.<ref name=Lepot2008>{{Cite journal
| doi = 10.1038/ngeo107
| volume = 1
| pages = 118–21
| last1 = Lepot
| first1 = Kevin
| first2=Karim |last2=Benzerara |first3=Gordon E. |last3=Brown |first4=Pascal |last4=Philippot
| title = Microbially influenced formation of 2.7 billion-year-old stromatolites
| journal = [[Nature Geoscience]]
| year = 2008
| issue=2
|bibcode = 2008NatGe...1..118L }}</ref>

A 2009 discovery provides strong evidence of microbial stromatolites extending as far back as 3.45&nbsp;billion years ago.<ref name=Allwood2009>{{Cite journal
| last1 = Allwood
| first1 = Abigail C.
|first2=John P. |last2=Grotzinger |first3=Andrew H. |last3=Knoll |first4=Ian W. |last4=Burch |first5=Mark S. |last5=Anderson |first6=Max L. |last6=Coleman |first7=Isik |last7=Kanik
| title = Controls on development and diversity of Early Archean stromatolites
| journal = Proceedings of the National Academy of Sciences
| year = 2009
| doi = 10.1073/pnas.0903323106
| volume = 106
| pages = 9548–9555
| issue = 24
|bibcode = 2009PNAS..106.9548A
| pmid=19515817
| pmc=2700989| doi-access = free
}}</ref><ref>{{cite book |title=Cradle of life: the discovery of earth's earliest fossils |first=J. William |last=Schopf |publisher=Princeton University Press |location=Princeton, N.J |year=1999 |url=https://books.google.com/books?id=YJHBAolcIk8C&pg=PA87 |pages=87–89 |isbn=978-0-691-08864-8 |access-date=11 October 2018 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317062709/https://books.google.com/books?id=YJHBAolcIk8C&pg=PA87 |url-status=live }}</ref>

Stromatolites are a major constituent of the fossil record for life's first 3.5&nbsp;billion years, peaking about 1.25&nbsp;billion years ago.<ref name=Allwood2009 /> They subsequently declined in abundance and diversity,<ref>{{cite journal| year=1982 | title=Precambrian conical stromatolites from California and Sonora | author=McMenamin, M. A. S. | journal=Bulletin of the Southern California Paleontological Society | volume=14 | issue=9&10 | pages=103–105 }}</ref> which by the start of the Cambrian had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victims to grazing creatures (the [[Cambrian substrate revolution]]), implying that sufficiently complex organisms were common over 1&nbsp;billion years ago.<ref name="McNamara1996DatingOriginAnimals">{{cite journal
 | author = McNamara, K.J.
 | title = Dating the Origin of Animals
 | journal = Science
 | volume = 274
 | pages = 1993–1997
 | date = 20 December 1996
 | doi = 10.1126/science.274.5295.1993f
 | issue = 5295
 | bibcode = 1996Sci...274.1993M
 | doi-access = free
 }}</ref><ref name="AwramikStromatoliteDiversityMetazoanAppearance">{{cite journal
 | author = Awramik, S.M.
 | title = Precambrian columnar stromatolite diversity: Reflection of metazoan appearance
 | journal = Science
 | volume = 174
 | pages = 825–827
 | date = 19 November 1971
 | doi=10.1126/science.174.4011.825
 | pmid = 17759393
 | issue=4011
|bibcode = 1971Sci...174..825A | s2cid = 2302113
 }}</ref><ref name="Bengtson2002OriginsOfPredation">{{Cite encyclopedia
 | author=Bengtson, S.
 | year=2002
 | chapter=Origins and early evolution of predation
 | encyclopedia=The Paleontological Society Papers
 | volume=8
 | title=The fossil record of predation
 | editor=Kowalewski, M. |editor2=Kelley, P.H.
 | pages=289–317
 | publisher=The Paleontological Society
 | chapter-url=http://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf |archive-url=https://web.archive.org/web/20080910205539/http://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf |archive-date=2008-09-10 |url-status=live
 | access-date=29 December 2014
}}</ref>

The connection between grazer and stromatolite abundance is well documented in the younger [[Ordovician]] [[evolutionary radiation]]; stromatolite abundance also increased after the [[Ordovician-Silurian extinction events|end-Ordovician]] and [[Permian extinction|end-Permian extinctions]] decimated marine animals, falling back to earlier levels as marine animals recovered.<ref name="SheehanHarris2004ResurgenceAfterOrdovicianExtinction">{{cite journal
| title=Microbialite resurgence after the Late Ordovician extinction
| journal=Nature
| volume=430
| pages=75–78
| year=2004
| doi=10.1038/nature02654
| author1=Sheehan, P.M. |author2=Harris, M.T.
| pmid=15229600
| issue=6995
| bibcode=2004Natur.430...75S
| s2cid=4423149
}}</ref> Fluctuations in [[metazoan]] population and diversity may not have been the only factor in the reduction in stromatolite abundance. Factors such as the chemistry of the environment may have been responsible for changes.<ref name="Riding2006">{{cite journal | url=http://www.robertriding.com/pdf/riding2006mc.pdf | title=Microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time | author=Riding R | journal=Sedimentary Geology | date=March 2006 | volume=185 | issue=3–4 | pages=229–38 | doi=10.1016/j.sedgeo.2005.12.015 | bibcode=2006SedG..185..229R | access-date=9 December 2011 | archive-url=https://web.archive.org/web/20120426041343/http://www.robertriding.com/pdf/riding2006mc.pdf | archive-date=26 April 2012 | url-status=dead }}</ref>

While [[prokaryote|prokaryotic]] cyanobacteria themselves reproduce asexually through cell division, they were instrumental in priming the environment for the [[timeline of evolution|evolutionary development]] of more complex [[eukaryote|eukaryotic]] organisms. Cyanobacteria (as well as [[extremophile]] [[Gammaproteobacteria]]) are thought to be largely responsible for increasing the amount of [[oxygen]] in the primeval Earth's [[atmosphere]] through their continuing [[photosynthesis]]. Cyanobacteria use [[water]], [[carbon dioxide]] and [[sunlight]] to create their food. A layer of [[mucus]] often forms over mats of cyanobacterial cells. In modern microbial mats, debris from the surrounding habitat can become trapped within the mucus, which can be cemented by the calcium carbonate to grow thin laminations of [[limestone]]. These laminations can accrete over time, resulting in the banded pattern common to stromatolites. The domal morphology of biological stromatolites is the result of the vertical growth necessary for the continued infiltration of sunlight to the organisms for photosynthesis. Layered spherical growth structures termed [[oncolite]]s are similar to stromatolites and are also known from the [[fossil record]]. [[Thrombolite]]s are poorly laminated or non-laminated clotted structures formed by cyanobacteria common in the fossil record and in modern sediments.<ref name=Lepot2008 />

The Zebra River Canyon area of the Kubis platform in the deeply dissected Zaris Mountains of southwestern [[Namibia]] provides an extremely well exposed example of the thrombolite-stromatolite-metazoan reefs that developed during the Proterozoic period, the stromatolites here being better developed in updip locations under conditions of higher current velocities and greater sediment influx.<ref>{{cite journal |author1=Adams, E. W. |author2=Grotzinger, J. P. |author3=Watters, W. A. |author4=Schröder, S. |author5=McCormick, D. S. |author6=Al-Siyabi, H. A. |year=2005 |title=Digital characterization of thrombolite-stromatolite reef distribution in a carbonate ramp system (terminal Proterozoic, Nama Group, Namibia) |journal=AAPG Bulletin |volume=89 |issue=10 |pages=1293–1318 |doi=10.1306/06160505005 |bibcode=2005BAAPG..89.1293A |url=http://www.wellesley.edu/Astronomy/Wwatters/adams%20etal%20-%20digital%20models%20nama%20reefs%20-%20aapg%20bull%202005.pdf |access-date=8 December 2011 |archive-url=https://web.archive.org/web/20160307215400/http://wellesley.edu/Astronomy/wwatters/adams%20etal%20-%20digital%20models%20nama%20reefs%20-%20aapg%20bull%202005.pdf |archive-date=7 March 2016 |url-status=dead }}</ref>

== Pseudofossils ==
[[File:Dendrites01.jpg|thumb|An example of a pseudofossil: Manganese [[Dendrite_(crystal)|dendrites]] on a limestone bedding plane from [[Solnhofen]], Germany; scale in mm]]

{{Main|Pseudofossils}}

''Pseudofossils'' are visual patterns in rocks that imitate fossils but are produced by geologic processes rather than biologic processes. Some pseudofossils, such as geological [[Dendrite (crystal)|dendrite]] crystals, are formed by naturally occurring fissures in the rock that get filled up by percolating minerals. Other types of pseudofossils are kidney ore (round shapes in iron ore) and [[moss agate]]s, which look like moss or plant leaves. [[Concretion]]s, spherical or ovoid-shaped nodules found in some sedimentary strata, were once thought to be [[dinosaur]] eggs and are often mistaken for fossils as well.

== Astrobiology ==
It has been suggested that [[biomineralization|biominerals]] could be important indicators of [[extraterrestrial life]] and thus could play an important role in the search for past or present life on the planet [[Mars]]. Furthermore, [[organic compounds (minerals)|organic components]] ([[biosignature]]s) that are often associated with biominerals are believed to play crucial roles in both pre-biotic and [[biotic material|biotic]] reactions.<ref name=SSG>{{Cite book |editor2-first=David |editor2-last=Beaty |chapter=Final report of the MEPAG Astrobiology Field Laboratory Science Steering Group (AFL-SSG) |title=The Astrobiology Field Laboratory |editor1-first=Andrew |editor1-last=Steele |publisher=[[Mars Exploration Program Analysis Group]] (MEPAG) – NASA |place=U.S. |page=72 |date=26 September 2006 |chapter-url=http://mepag.jpl.nasa.gov/reports/AFL_SSG_WHITE_PAPER_v3.doc |chapter-format=.doc |access-date=29 December 2014 |author=The MEPAG Astrobiology Field Laboratory Science Steering Group |archive-date=11 May 2020 |archive-url=https://web.archive.org/web/20200511055338/https://mepag.jpl.nasa.gov/reports/AFL_SSG_WHITE_PAPER_v3.doc |url-status=live }}</ref>

On 24 January 2014, NASA reported that current studies by the [[Curiosity (rover)|''Curiosity'']] and [[Opportunity (rover)|''Opportunity'']] [[Mars rover|rovers]] on Mars would begin searching for evidence of ancient life, including a [[biosphere]] based on [[autotroph]]ic, [[chemotroph]]ic and/or [[Chemolithotrophs|chemolithoautotrophic]] [[microorganism]]s, as well as ancient water, including [[Lacustrine plain|fluvio-lacustrine environments]] ([[plain]]s related to ancient [[river]]s or [[lake]]s) that may have been [[Planetary habitability|habitable]].<ref name="SCI-20140124a">{{cite journal |last=Grotzinger |first=John P.|title=Introduction to Special Issue – Habitability, Taphonomy, and the Search for Organic Carbon on Mars|journal=[[Science (journal)|Science]] |date=24 January 2014 |volume=343 |number=6169 |pages=386–387 |doi=10.1126/science.1249944 |bibcode=2014Sci...343..386G |pmid=24458635|doi-access=free }}</ref><ref name="SCI-20140124special">{{cite journal |author=Various |title=Special Issue – Table of Contents – Exploring Martian Habitability |url=https://www.science.org/toc/science/343/6169 |date=24 January 2014 |journal=[[Science (journal)|Science]] |volume=343 |number=6169 |pages=345–452 |access-date=24 January 2014 |archive-url=https://web.archive.org/web/20140129042127/http://www.sciencemag.org/content/343/6169.toc#SpecialIssue |archive-date=29 January 2014 |url-status=live }}</ref><ref name="SCI-20140124">{{cite journal |author=Various |title=Special Collection – Curiosity – Exploring Martian Habitability |url=https://www.science.org/action/doSearch?AllField=Curiosity+Mars |date=24 January 2014 |journal=[[Science (journal)|Science]] |access-date=24 January 2014 |archive-url=https://web.archive.org/web/20140128102653/http://www.sciencemag.org/site/extra/curiosity/ |archive-date=28 January 2014 |url-status=live }}</ref><ref name="SCI-20140124c">{{cite journal|author=Grotzinger, J.P. |title=A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars |date=24 January 2014 |journal=[[Science (journal)|Science]] |volume=343 |number=6169 |doi=10.1126/science.1242777 |page=1242777|bibcode = 2014Sci...343A.386G |display-authors=etal |pmid=24324272|citeseerx=10.1.1.455.3973 |s2cid=52836398 }}</ref> The search for evidence of [[Planetary habitability|habitability]], [[taphonomy]] (related to fossils), and [[organic carbon]] on the planet [[Mars]] is now a primary [[NASA]] objective.<ref name="SCI-20140124a" /><ref name="SCI-20140124special" />

== Art ==
According to one hypothesis, a Corinthian vase from the 6th century BCE (Boston 63.420) is the oldest artistic record of a vertebrate fossil, perhaps a Miocene giraffe combined with elements from other species.<ref>{{ cite journal
| last=Mayor |first= A. |year=2000
|title=The "Monster of Troy" Vase: The Earliest Artistic Record of a Vertebrate Fossil Discovery? 
|journal=Oxford Journal of Archaeology
|volume=19 | issue=1
|pages=57–63
| doi= 10.1111/1468-0092.00099}}</ref> However, a later study by [[Julian_Monge_Najera|Julián Monge-Nájera]] using expert evaluations rejects this idea, because mammals do not have the [[sclerotic ring|eye bones]] shown on the painted monster. Monge-Nájera believes the morphology shown in the vase painting corresponds best to an extant [[Varanidae|varanid]] that would have been known to the Ancient Greeks.<ref>{{Cite journal|last=Monge-Nájera|first=Julián|date=2020-01-31|title=Evaluation of the hypothesis of the Monster of Troy vase as the earliest artistic record of a vertebrate fossil|url=https://www.revistas.una.ac.cr/index.php/uniciencia/article/view/12556|journal=Uniciencia|language=en|volume=34|issue=1|pages=147–151|doi=10.15359/ru.34-1.9|s2cid=208591414|issn=2215-3470|access-date=20 February 2023|archive-date=20 February 2023|archive-url=https://web.archive.org/web/20230220171054/https://www.revistas.una.ac.cr/index.php/uniciencia/article/view/12556|url-status=live|doi-access=free}}</ref>

== Trading and collecting ==
{{Main|Fossil trading|Fossil collecting}}

Fossil trading is the practice of buying and selling fossils. This is often done illegally with artifacts stolen from research sites, costing many important scientific specimens each year.<ref>{{cite news | url=https://www.independent.co.uk/news/science/fossil-theft-one-of-our-dinosaurs-is-missing-1826931.html | work=The Independent | location=London | title=Fossil theft: One of our dinosaurs is missing | first=Cahal | last=Milmo | date=25 November 2009 | access-date=2 May 2010 | archive-url=https://web.archive.org/web/20091128064539/http://www.independent.co.uk/news/science/fossil-theft-one-of-our-dinosaurs-is-missing-1826931.html | archive-date=28 November 2009 | url-status=live }}<br />{{cite web|url=http://science.nationalgeographic.com/science/prehistoric-world/fossil-wars.html|title=Fossil Wars|last=Simons|first=Lewis|work=National Geographic|publisher=The [[National Geographic Society]]|access-date=29 February 2012|archive-url=https://web.archive.org/web/20120227170051/http://science.nationalgeographic.com/science/prehistoric-world/fossil-wars.html|archive-date=27 February 2012|url-status=dead}}<br />{{cite web|url=http://www.abc.net.au/catalyst/stories/s532586.htm|title=Fossil Trade|work=Catalyst|date=18 April 2002|author1=Willis, Paul|author2=Clark, Tim|author3=Dennis, Carina|access-date=29 February 2012|archive-url=https://web.archive.org/web/20120524090915/http://www.abc.net.au/catalyst/stories/s532586.htm|archive-date=24 May 2012|url-status=live}}<br />{{cite web|url=http://www.timeshighereducation.co.uk/story.asp?storyCode=148688&sectioncode=26|title=Cretaceous crimes that fuel the fossil trade|last=Farrar|first=Steve|date=5 November 1999|work=Times Higher Education|access-date=2 November 2011|archive-url=https://web.archive.org/web/20120820030843/http://www.timeshighereducation.co.uk/story.asp?storyCode=148688&sectioncode=26|archive-date=20 August 2012|url-status=live}}</ref> The problem is quite pronounced in China, where many specimens have been stolen.<ref>{{Cite magazine|last=Williams|first=Paige|title=The Black Market for Dinosaurs|url=https://www.newyorker.com/tech/annals-of-technology/the-black-market-for-dinosaurs|access-date=7 September 2020|magazine=The New Yorker|language=en-us|archive-date=22 September 2020|archive-url=https://web.archive.org/web/20200922223219/https://www.newyorker.com/tech/annals-of-technology/the-black-market-for-dinosaurs|url-status=live}}</ref>

Fossil collecting (sometimes, in a non-scientific sense, fossil hunting) is the collection of fossils for scientific study, leisure, or profit. Amateur fossil collecting is the predecessor of modern paleontology and remains a practiced hobby to date. Professionals and amateurs alike collect fossils for their scientific value.

== As medicine ==
The use of fossils to address health issues is rooted in [[traditional medicine]] and include the use of fossils as [[talisman]]s. The specific fossil to use to alleviate or cure an illness is often based on its resemblance to the symptoms or affected organ (see [[sympathetic magic]]). The usefulness of fossils as medicine is almost entirely a [[placebo effect]], though fossil material might conceivably have some [[antacid]] activity or supply some [[mineral (nutrient)|essential mineral]]s.<ref>{{cite journal |last1=van der Geer |first1=Alexandra |last2=Dermitzakis |first2=Michael |date=2010 |title=Fossils in pharmacy: from "snake eggs" to "Saint's bones"; an overview |url=http://www.hellenjgeosci.geol.uoa.gr/45/van%20der%20Geer%20&%20Dermitzakis.pdf |journal=[[Hellenic Journal of Geosciences]] |volume=45 |pages=323–332 |archive-url=https://web.archive.org/web/20130619041702/http://www.hellenjgeosci.geol.uoa.gr/45/van%20der%20Geer%20%26%20Dermitzakis.pdf |archive-date=19 June 2013 |url-status=dead }}</ref> The use of dinosaur bones as "dragon bones" has persisted in [[Traditional Chinese medicine]] into modern times, with mid-Cretaceous dinosaur bones being consumed in [[Ruyang County]] during the early 21st century.<ref>{{Cite web|url=https://www.nbcnews.com/id/wbna19606626|title=Chinese villagers ate dinosaur 'dragon bones'|agency=[[Associated Press]]|date=5 July 2007|publisher=[[MSNBC]]|language=en|access-date=7 March 2020|archive-url=https://web.archive.org/web/20200122072720/http://www.nbcnews.com/id/19606626/ns/world_news-asia_pacific/t/chinese-villagers-ate-dinosaur-dragon-bones|archive-date=22 January 2020|url-status=live}}</ref>

== Gallery ==
<gallery widths="200" heights="200">
File:Marine fossils found high in the Himalayas. Collection of the Abbot of Dhankar Gompa, HP, India.jpg|Marine fossils found high in the Himalayas. Collection of the Abbot of [[Dhankar Gompa]], HP, India
File:Amonite Cropped.jpg|Three small [[ammonite]] fossils, each approximately 1.5&nbsp;cm across
File:Cockerellites liops Green River Formation.jpg|[[Eocene]] fossil fish ''Priscacara liops'' from the [[Green River Formation]] of Wyoming
File:Trilobite2.jpg|A permineralized [[trilobite]], ''[[Asaphus kowalewskii]]''
File:Carcharodontosaurus and Megalodon teeth.jpg|[[Megalodon]] and ''[[Carcharodontosaurus]]'' teeth. The latter was found in the [[Sahara Desert]].
File:The fossils from Cretaceous age found in Lebanon.jpg|Fossil [[shrimp]] ([[Cretaceous]])
File:PetrifiedWood.jpg|Petrified wood in [[Petrified Forest National Park]], Arizona
File:Petrified Araucaria cone from patagonia-Edit3.jpg|Petrified [[Conifer cone|cone]] of ''[[Araucaria mirabilis]]'' from [[Patagonia]], [[Argentina]] dating from the [[Jurassic Period]] (approx. 210 [[Ma (unit)|Ma]])
File:CyprusPlioceneGastropod.JPG|A fossil [[gastropod]] from the [[Pliocene]] of [[Cyprus]]. A [[Serpulidae|serpulid worm]] is attached.
File:OrhtocerasNautiloid092313.jpg|[[Silurian]] [[Orthoceras]] fossil
File:Eocene fossil flower, Clare Family Florissant Fossil Quarry, Florissant, Colorado, USA - 20100807.jpg|Eocene fossil flower from Florissant, Colorado
File:RoyLindmanMicraster.JPG|''[[Micraster]]'' [[echinoid]] fossil from England
File:Productid Permian Texas.JPG|Productid [[brachiopod]] ventral valve; Roadian, [[Guadalupian]] (Middle [[Permian]]); Glass Mountains, Texas.
File:Fossil agatized coral Florida.JPG|[[Agate|Agatized]] [[coral]] from the [[Hawthorn Group]] ([[Oligocene]]–[[Miocene]]), [[Florida]]. An example of preservation by replacement.
File:Fossils from Gotland beaches.jpg|Fossils from beaches of the [[Baltic Sea]] island of [[Gotland]], placed on paper with 7&nbsp;mm (0.28 inch) squares
File:Dinosaur footprints in ToroToro Bolivia.jpg|Dinosaur footprints from [[Torotoro National Park]] in Bolivia.
</gallery>

== See also ==
{{Portal|Paleontology|Geology}}
{{Div col}}
* {{annotated link|Bioerosion}}
* {{annotated link|Cryptospore}}
* {{annotated link|Endolith}}
* {{annotated link|List of fossil parks}}
* {{annotated link|Living fossil}}
* {{annotated link|Paleobiology}}
* {{annotated link|Paleobotany}}
* {{annotated link|Schultz's rule}}
* {{annotated link|Shark tooth}}
* {{annotated link|Signor–Lipps effect}}
{{Div col end}}

== References ==
{{Reflist}}

== Further reading ==
* [https://www.msn.com/en-us/news/us/grand-canyon-cliff-collapse-reveals-313-million-year-old-fossil-footprints/ar-BB18dTeR?ocid=spartan-ntp-feeds "Grand Canyon cliff collapse reveals 313 million-year-old fossil footprints"] 21 August 2020, ''[[CNN]]''
* [https://web.archive.org/web/20200304045107/https://www.nationalgeographic.com/science/2020/03/hints-of-dna-discovered-in-a-dinosaur-fossil/ "Hints of fossil DNA discovered in dinosaur skull"] by Michael Greshko, 3 March 2020, ''[[National Geographic]]''
* [https://www.youtube.com/watch?v=tyOjxjFHW-c "Fossils for Kids | Learn all about how fossils are formed, the types of fossils and more!"] Video (2:23), 27 January 2020, ''Clarendon Learning''
* [https://www.khanacademy.org/science/in-in-class-10-biology/in-in-heredity-and-evolution/in-in-evolution-classification/v/fossils-their-formation-heredity-evolution-biology-khan-academy "Fossil & their formation"] Video (9:55), 15 November 2019, ''[[Khan Academy]]''
* [https://www.nhm.ac.uk/discover/how-are-fossils-formed.html "How are dinosaur fossils formed?] by Lisa Hendry, ''[[Natural History Museum, London]]''
* [https://www.youtube.com/watch?v=bRuSmxJo_iA "Fossils 101"] Video (4:27), 22 August 2019, ''[[National Geographic]]''
* [https://www.atlasobscura.com/articles/find-fossils-urban-geology? "How to Spot the Fossils Hiding in Plain Sight"] by Jessica Leigh Hester, 23 February 2018, ''[[Atlas Obscura]]''
* [http://judson.blogs.nytimes.com/2008/12/30/reflections-on-an-oyster/ "It's extremely hard to become a fossil"] {{Webarchive|url=https://web.archive.org/web/20090904085750/http://judson.blogs.nytimes.com/2008/12/30/reflections-on-an-oyster/ |date=4 September 2009 }}, by [[Olivia Judson]], 30 December 2008, ''[[The New York Times]]''
* [http://judson.blogs.nytimes.com/2008/03/04/bones-are-not-the-only-fossils/ "Bones Are Not the Only Fossils"] {{Webarchive|url=https://web.archive.org/web/20090315163045/http://judson.blogs.nytimes.com/2008/03/04/bones-are-not-the-only-fossils/ |date=15 March 2009 }}, by [[Olivia Judson]], 4 March 2008, ''[[The New York Times]]''

== External links ==
{{Wikibooks|Historical Geology|Fossils}}
{{Wikibooks|Historical Geology|Fossils and absolute dating}}
{{Wikiquote}}
{{Wiktionary|fossil}}
{{Commons category|lcfirst=yes}}
* {{In Our Time|Fossils|p00547d3|Fossils}}
* [http://www.fossilmuseum.net/ The Virtual Fossil Museum throughout Time and Evolution]
* [http://www.paleoportal.org/ Paleoportal, geology and fossils of the United States] {{Webarchive|url=https://web.archive.org/web/20090930070415/http://www.paleoportal.org/ |date=30 September 2009 }}
* [https://web.archive.org/web/20120503234246/http://www.fossilrecord.net/ The Fossil Record, a complete listing of the families, orders, class and phyla found in the fossil record] (archived 3 May 2012)
* {{Cite Americana|wstitle=Fossils|author=[[Ernest Ingersoll]]|short=x}}
* {{Cite NIE|wstitle=Fossil|short=x}}

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[[Category:Fossils| ]]