Editing Trace fossil (section)

== Evolution ==
[[Image:Climactichnites - Todd Gass.jpg|thumb|''[[Climactichnites]] wilsoni'', probably trails from a slug-like animal, from the [[Cambrian]], [[Blackberry Hill]], central [[Wisconsin]]. The ruler in the background is {{convert|45|cm|in|abbr=on}} long.]]
The earliest complex trace fossils, not including microbial traces such as [[stromatolites]], date to {{Ma|2000|1800}}. This is far too early for them to have an animal origin, and they are thought to have been formed by [[amoeba]]e.<ref name='Bengtson2009'>{{cite journal
 | doi = 10.1126/science.1168794
 |date=January 2009
 |author1=Bengtson, S |author2=Rasmussen, B | title = Paleontology. New and ancient trace makers
 | volume = 323
 | issue = 5912
 | pages = 346–7
 | pmid = 19150833
 | journal = Science |hdl=20.500.11937/24668
 |s2cid=1922434
 | hdl-access = free
 }}</ref>
Putative "burrows" dating as far back as {{Ma|1100|million years}} may have been made by animals which fed on the undersides of microbial mats, which would have shielded them from a chemically unpleasant ocean;<ref name=Seilacher1998>{{cite journal
 | author = Seilacher, A.
 | author-link = Adolf Seilacher |author2=Bose, P.K. |author3=Pflüger, F.
 | date = 1998-10-02
 | title = Triploblastic Animals More Than 1 Billion Years Ago: Trace Fossil Evidence from India
 | journal = Science
 | volume = 282
 | issue = 5386
 | pages = 80–83
 | doi = 10.1126/science.282.5386.80
 | pmid = 9756480
 |bibcode = 1998Sci...282...80S }}</ref> however their uneven width and tapering ends make a biological origin so difficult to defend<ref name=Budd2000>{{cite journal
 | author = Budd, G.E.
 |author2=Jensen, S.
 | year = 2000
 | title = A critical reappraisal of the fossil record of the bilaterian phyla
 | journal = Biological Reviews
 | volume = 75
 | issue = 2
 | pages = 253–295
 | doi = 10.1111/j.1469-185X.1999.tb00046.x
 | url = http://www.journals.cambridge.org/abstract_S000632310000548X
 | format = abstract
| pmid=10881389|s2cid=39772232
 | url-access = subscription
 }}</ref> that even the original author no longer believes they are authentic.<ref>{{cite journal
 | doi = 10.1126/science.1166220
 | title = PALEONTOLOGY: Reading Behavior from the Rocks
 | year = 2008
 | author = Jensen, S.
 | journal = Science
 | volume = 322
 | pages = 1051–1052
 | issue = 5904 | s2cid = 129734373
 }}</ref>

The first evidence of burrowing which is widely accepted dates to the [[Ediacaran]] (Vendian) period, around {{Ma|560}}.<ref>{{Cite web|url=https://www.palaeontologyonline.com/articles/2017/fossil-focus-ediacaran-biota/|title=Fossil Focus: The Ediacaran Biota|last=Frances S. Dunn and Alex G. Liu|date=2017|website=Paleontology Online}}</ref> During this period the traces and burrows basically are horizontal on or just below the seafloor surface. Such traces must have been made by motile organisms with heads, which would probably have been [[bilateria|bilateran]] [[animal]]s.<ref>{{cite book
 | author = Fedonkin, M.A.
 | year = 1992
 | title = Vendian faunas and the early evolution of Metazoa
 | journal = In Lipps, J., and Signor, P. W., Eds., Origin and Early Evolution of the Metazoa: New York, Plenum Press.
 | pages = 87–129
 | url = https://books.google.com/books?id=gUQMKiJOj64C&pg=PP1
 | isbn = 978-0-306-44067-0
 | publisher = Springer
 | access-date = 2007-03-08
 }}</ref> The traces observed imply simple behaviour, and point to organisms feeding above the surface and burrowing for protection from predators.<ref name=Dzik2007>
{{The Rise and Fall of the Ediacaran Biota|author=Dzik, J |chapter=The Verdun Syndrome: simultaneous origin of protective armour and infaunal shelters at the Precambrian–Cambrian transition |pages=405-414 |doi=10.1144/SP286.30}}</ref> Contrary to widely circulated opinion that Ediacaran burrows are only horizontal the vertical burrows ''[[Skolithos]]'' are also known.<ref name=Fedonkin_1985>M. A. Fedonkin (1985). "Paleoichnology of Vendian Metazoa". In Sokolov, B. S. and Iwanowski, A. B., eds., "Vendian System: Historical–Geological and Paleontological Foundation, Vol. 1: Paleontology". Moscow: Nauka, pp. 112–116. (in Russian)</ref> The producers of burrows ''[[Skolithos]] declinatus'' from the Vendian (Ediacaran) beds in [[Russia]] with date {{Ma|555.3}} have not been identified; they might have been filter feeders subsisting on the nutrients from the suspension. The density of these burrows is up to 245 burrows/dm<sup>2</sup>.<ref>{{cite journal|last=Grazhdankin|first=D. V.|author2=A. Yu. Ivantsov |year=1996|title=Reconstruction of biotopes of ancient Metazoa of the Late Vendian White Sea Biota|journal=Paleontological Journal|volume=30|pages=676–680}}</ref> Some Ediacaran trace fossils have been found directly associated with body fossils. ''[[Yorgia]]'' and ''[[Dickinsonia]]'' are often found at the end of long pathways of trace fossils matching their shape.<ref name=Ivantsov2002>{{cite journal
 |author      = Ivantsov, A.Y.
 |author2     = Malakhovskaya, Y.E.
 |year        = 2002
 |title       = Giant Traces of Vendian Animals
 |journal     = Doklady Earth Sciences
 |volume      = 385
 |issue       = 6
 |pages       = 618–622
 |issn        = 1028-334X
 |url         = http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf
 |access-date  = 2007-05-10
 |archive-url  = https://web.archive.org/web/20070704183947/http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf
 |archive-date = 2007-07-04
}}</ref> The feeding was performed in a mechanical way, supposedly the ventral side of body these organisms was covered with [[cilia]].<ref name=Oslo_2008>A. Yu. Ivantsov. (2008). [http://www.cprm.gov.br/33IGC/1323085.html "Feeding traces of the Ediacaran animals"]. HPF-17 Trace fossils ? ichnological concepts and methods. International Geological Congress - Oslo 2008.</ref> The potential [[mollusc]] related ''[[Kimberella]]'' is associated with scratch marks, perhaps formed by a [[radula]],<ref name=Fedonkin2007>{{The Rise and Fall of the Ediacaran Biota |chapter=New data on ''Kimberella'', the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications |author=Fedonkin, M.A. |author2=Simonetta, A |author3=Ivantsov, A.Y. |pages=157–179 |doi=10.1144/SP286.12}}</ref> further traces from {{Ma|555}} appear to imply active crawling or burrowing activity.<ref name=Martin2000>According to {{cite journal
 | author = Martin, M.W.
 |author2=Grazhdankin, D.V. |author3=Bowring, S.A. |author4=Evans, D.A.D. |author5=Fedonkin, M.A. |author6= Kirschvink, J.L. 
 | date = 2000-05-05
 | title = Age of Neoproterozoic Bilatarian 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 |s2cid=1019572 }}</ref>

As the [[Cambrian]] got underway, new forms of trace fossil appeared, including vertical burrows (e.g. ''[[Diplocraterion]]'') and traces normally attributed to [[arthropod]]s.<ref>Such as ''[[Cruziana]]'' and ''[[Rusophycus]]''. Details of Cruziana's formation are reported by {{cite journal
 | author = Goldring, R.
 | date =  January 1, 1985 | title = The formation of the trace fossil Cruziana
 | journal = Geological Magazine
 | volume = 122
 | issue = 1
 | pages = 65–72
 | url = http://geolmag.geoscienceworld.org/cgi/content/abstract/122/1/65
 | access-date = 2007-09-09
 | doi = 10.1017/S0016756800034099
 | bibcode = 1985GeoM..122...65G
 | s2cid = 130340569 | url-access = subscription
 }}</ref> These represent a "widening of the behavioural repertoire",<ref name=ConwayMorris1989>{{cite journal
 | author = Conway Morris, S.
 | year = 1989
 | title = Burgess Shale Faunas and the Cambrian Explosion
 | journal = Science
 | volume = 246
 | issue = 4928
 | pages = 339–46
 | doi = 10.1126/science.246.4928.339
 | pmid = 17747916
 | bibcode=1989Sci...246..339C
| s2cid = 10491968
 }}</ref> both in terms of abundance and complexity.<ref>{{cite journal
| title=The Proterozoic and Earliest Cambrian Trace Fossil Record; Patterns, Problems and Perspectives
| author=Jensen, S.
| journal=Integrative and Comparative Biology
| volume=43
| year=2003
| pages=219–228
| doi = 10.1093/icb/43.1.219
| issue=1
 | pmid=21680425| doi-access=free
}}</ref>

Trace fossils are a particularly significant source of data from this period because they represent a data source that is not directly connected to the presence of easily fossilized hard parts, which are rare during the Cambrian. Whilst exact assignment of trace fossils to their makers is difficult, the trace fossil record seems to indicate that at the very least, large, bottom-dwelling, [[Symmetry (biology)#Bilateral symmetry|bilaterally symmetrical]] organisms were rapidly diversifying during the early [[Cambrian]].<ref>Although some [[cnidaria]]ns are effective burrowers, e.g. {{cite journal
 |author       = Weightman, J.O.
 |author2      = Arsenault, D.J.
 |year         = 2002
 |title        = Predator classification by the sea pen ''Ptilosarcus gurneyi'' (Cnidaria): role of waterborne chemical cues and physical contact with predatory sea stars
 |volume       = 80
 |issue        = 1
 |pages        = 185–190
 |doi          = 10.1139/z01-211
 |url          = http://pubs.nrc-cnrc.gc.ca/rp/rppdf/z01-211.pdf
 |access-date   = 2007-04-21
 |journal      = Canadian Journal of Zoology
 |archive-url  = https://web.archive.org/web/20070927211505/http://pubs.nrc-cnrc.gc.ca/rp/rppdf/z01-211.pdf
 |archive-date = 2007-09-27
 }} most Cambrian trace fossils have been assigned to bilaterian animals.</ref>

Further, less rapid{{Verify source|date=April 2008}} diversification occurred since,{{Verify source|date=April 2008}} and many traces have been converged upon independently by unrelated groups of organisms.<ref name=Seilacher1967/>

Trace fossils also provide our earliest evidence of animal life on land.<ref>{{Cite news|url=https://phys.org/news/2017-06-life-terra-firma-began-invasion.html|title=Life on terra firma began with an invasion|work=Phys.org News|access-date=2017-06-04}}</ref> Evidence of the first animals that appear to have been fully terrestrial dates to the Cambro-Ordovician and is in the form of trackways.<ref name=MacNaughton2002>{{cite journal
 | author = MacNaughton, R.B.
 |author2=Cole, J.M. |author3=Dalrymple, R.W. |author4=Braddy, S.J. |author5=Briggs, D.E.G. |author6= Lukie, T.D. 
 | year = 2002
 | title = First steps on land: Arthropod trackways in Cambrian-Ordovician eolian sandstone, southeastern Ontario, Canada
 | journal = Geology
 | volume = 30
 | issue = 5
 | pages = 391–394
 | doi = 10.1130/0091-7613(2002)030<0391:FSOLAT>2.0.CO;2
 | issn = 0091-7613
 | bibcode=2002Geo....30..391M
|s2cid=130821454 }}</ref> Trackways from the Ordovician [[Tumblagooda sandstone]] allow the behaviour of other terrestrial organisms to be determined.<ref name=Trewin1995/> The trackway ''[[Protichnites]]'' represents traces from an amphibious or terrestrial arthropod going back to the Cambrian.<ref name="ColletteEtAl2012">{{cite journal |last1=Collette |first1=J.H. |last2=Gass |first2=K.C. |last3=Hagadorn |first3=J.W. |title=Protichnites eremita unshelled? Experimental model-based neoichnology and new evidence for a euthycarcinoid affinity for this ichnospecies |journal=Journal of Paleontology |year=2012 |volume=86 |issue=3 |pages=442–454 |doi=10.1666/11-056.1|bibcode=2012JPal...86..442C |s2cid=129234373 }}</ref>