Trace fossil 367492 226086793 2008-07-16T19:39:42Z Wilson44691 4349401 [[Image:Cheirotherium prints possibly Ticinosuchus.JPG|thumb|''[[Chirotherium]]'' footprints in a [[Triassic]] sandstone.]] [[Image:Protichnites.jpg|thumb|''[[Protichnites]]'' tracks from the late [[Cambrian]], central [[Wisconsin]].]] '''Trace fossils''', also called '''ichnofossils''' ({{IPAEng|ˈɪknoʊfɒsɨl}}, {{lang-el|ιχνος'' or ''ikhnos}} meaning "trace" or "track"), are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, [[burrow]]s, borings ([[bioerosion]]), footprints and feeding marks, and root cavities. The term in its broadest sense also includes the remains of other organic material produced by an organism - for example [[coprolite]]s (fossilized droppings) or chemical markers - or sedimentological structures produced by biological means - for example, [[stromatolites]]. Trace fossils contrast with body fossils, which are the fossilised remains of parts of organisms' bodies, usually altered by later chemical activity or mineralisation. Sedimentary structures, for example those produced by empty shells rolling along the sea floor, are not produced through the behaviour of an organism and not considered trace fossils. The study of traces is called [[ichnology]], which is divided into ''paleoichnology'', or the study of trace fossils, and ''neoichnology'', the study of modern traces. This science is challenging, as most traces reflect the behaviour--not the biological affinity--of their makers. As such, trace fossils are categorised into [[form genera]], based upon their appearance and the implied behaviour of their makers. ==Occurrence== [[Image:MammothFootImpressions25.jpg|thumb|right|Cross-section of [[mammoth]] footprints at The Mammoth Site, Hot Springs, South Dakota.]] Traces are better known in their fossilised form than in modern sediments.<ref name=Seilacher1967/> This makes it difficult to interpret some fossils by comparing them with modern traces, even though they may be extant or even common.<ref name=Seilacher1967/> The main difficulties in accessing extant burrows stem from finding them in consolidated sediment, and being able to access those formed in deeper water. Trace fossils are best preserved in sandstones;<ref name=Seilacher1967/> the grain size and depositional facies both contributing to the better preservation. They may also be found in shales and limestones.<ref name=Seilacher1967/> ==Classification== {{main|Trace fossil classification}} Trace fossils are generally difficult or impossible to assign to a specific maker. Only in very rare occasions are the makers found in association with their tracks. Further, entirely different organisms may produce identical tracks. Therefore conventional taxonomy is not applicable, and a comprehensive form taxonomy has been erected. At the highest level of the classification, five bahavioural modes are recognised:<ref name=Seilacher1967>{{cite journal | author = Seilacher, A. | year = 1967 | title = Bathymetry of trace fossils | journal = Marine Geology | volume = 5 | issue = 5-6 | doi = 10.1016/0025-3227(67)90051-5 | pages = 413–428 | issn = 0025-3227 }}</ref> * '''Domichnia''', dwelling structures reflecting the life position of the organism that created it. * '''Fodinichnia''', three-dimensional structures left by animals which eat their way through sediment, such as deposit feeders; * '''Pascichnia''', feeding traces left by grazers on the surface of a soft sediment or a mineral substrate; * '''Cubichnia''', resting traces, in the form of an impression left by an organism on a soft sediment; * '''Repichnia''', surface traces of creeping and crawling. Fossils are further classified into form genera, a few of which are even subdivided to a "species" level. Classification is based on shape, form, and implied behavioural mode. == Information provided by ichnofossils == Because identical fossils can be created by a range of different organisms, trace fossils can only reliably inform us of two things: the consistency of the sediment at the time of its deposition, and the energy level of the depositional environment.<ref name=Woolfe1990/> Attempts to deduce such traits as whether a deposit is marine or non-marine have been made, but shown to be unreliable.<ref name=Woolfe1990>{{cite journal | author = Woolfe, K.J. | year = 1990 | title = Trace fossils as paleoenvironmental indicators in the Taylor Group (Devonian) of Antarctica | journal = Palaeogeography, Palaeoclimatology, Palaeoecology | volume = 80 | pages = 301–310 | doi = 10.1016/0031-0182(90)90139-X }}</ref> === Paleoecology === Trace fossils provide us with indirect evidence of [[prehistoric life|life in the past]], such as the footprints, tracks, burrows, borings, and feces left behind by animals, rather than the preserved remains of the body of the actual animal itself. Unlike most other fossils, which are produced only after the death of the organism concerned, trace fossils provide us with a record of the activity of an organism during its lifetime. Trace fossils are formed by organisms performing the functions of their everyday life, such as walking, crawling, burrowing, boring, or feeding. [[Tetrapod]] footprints, [[worm]] trails and the burrows made by [[clam]]s and [[arthropods]] are all trace fossils. Perhaps the most spectacular trace fossils are the huge, three-toed footprints produced by [[dinosaur]]s and related [[archosaur]]s. These imprints give scientists clues as to how these animals lived. Although the skeletons of dinosaurs can be reconstructed, only their [[fossilized]] footprints can determine exactly how they stood and walked. Such tracks can tell much about the gait of the animal which made them, what its stride was, and whether or not the front limbs touched the ground. However, most trace fossils are rather less conspicuous, such as the trails made by [[segmented worm]]s or [[nematode]]s. Some of these [[worm]] castings are the only fossil record we have of these soft-bodied creatures. === Palæoenvironment === Fossil footprints made by tetrapod [[vertebrate]]s are difficult to identify to a particular species of animal, but they can provide us with valuable information such as the speed, weight, and behavior of the organism that made them. Such trace fossils are formed when [[amphibian]]s, [[reptile]]s, [[mammal]]s or [[bird]]s walked across soft (probably wet) mud or sand which later hardened sufficiently to retain the impressions before the next layer of sediment was deposited. Some fossils can even provide details of how wet the sand was when they were being produced, and hence allow estimation of palæo-wind directions.<ref name=Trewin1995>{{cite journal | author = Trewin, N.H. | coauthors = McNamara, K.J. | year = 1995 | title = Arthropods invade the land: trace fossils and palaeoenvironments of the Tumblagooda Sandstone (? late Silurian) of Kalbarri, Western Australia | journal = Transactions of the Royal Society of Edinburgh: Earth Sciences | volume = 85 | pages = 177–210 }}</ref> Assemblages of trace fossils occur at certain water depths,<ref name=Seilacher1967 /> and can also reflect the salinity and turbidity of the water column. === Stratigraphic correlation === Some trace fossils can be used as local [[index fossil]]s, to date the rocks in which they are found, such as the burrow ''[[Arenicolites]] franconicus'' which occurs only in a 4 cm (1.6") layer of the [[Triassic]] Muschelkalk epoch, throughout wide areas in southern [[Germany]].<ref name=Schlirf2006>{{cite journal | author = Schlirf, M. | year = 2006 | title = Trusheimichnus New Ichnogenus From the Middle Triassic of the Germanic Basin, Southern Germany | journal = Ichnos | volume = 13 | issue = 4 | pages = 249–254 | url = http://www.ingentaconnect.com/content/tandf/gich/2006/00000013/00000004/art00005 | accessdate = 2008-04-21 | doi = 10.1080/10420940600843690 }}</ref>{{Verify source|date=February 2007}} The base of the Cambrian period is defined by the first appearance of the trace fossil ''[[Trichophycus pedum]]''.<ref>{{Cite journal | last = Gehling | first = 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 | year = 2001 | url = http://www.journals.cambridge.org/action/displayAbstract?fromPage=online&aid=74669 | doi = 10.1017/S001675680100509X }} </ref> Trace fossils have a further utility as many appear before the organism thought to create them, extending their stratigraphic range.<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 | url = http://www.springerlink.com/index/WP279834395100KH.pdf | accessdate = 2007-09-09 }}</ref> ==Ichnofacies== {{main|ichnofacies}} Trace fossil assemblages are far from random; the range of fossils recorded in association is constrained by the environment in wheich the trace-making organisms dwelt.<ref name=Seilacher1967/> Palaeontologist [[Adolf Seilacher]] pioneered the concept of ichnofacies, whereby the state of a sedimentary system at its time of deposition could be implied by noting the fossils in association with one another.<ref name=Seilacher1967/> == Inherent bias == Most trace fossils are known from marine deposits.{{Fact|date=February 2007}} Essentially, there are two types of traces, either exogenic ones, which are made on the surface of the sediment (such as tracks) or endogenic ones, which are made within the layers of sediment (such as burrows). Surface trails on sediment in shallow marine environments stand less chance of fossilization because they are subjected to wave and current action. Conditions in quiet, deep-water environments tend to be more favorable for preserving fine trace structures. Most trace fossils are usually readily identified by reference to similar phenomena in modern environments. However, the structures made by organisms in recent sediment have only been studied in a limited range of environments, mostly in coastal areas, including [[tidal flat]]s.{{Fact|date=January 2008}} == Evolution == [[Image:Climactichnites - Todd Gass.jpg|thumb|''[[Climactichnites]]'', probably trackways from a slug-like animal, from the late [[Cambrian]], central [[Wisconsin]]. ''Ruler in background is 45cm (18") long.'']] 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;<!--Note that even Seilacher himself no longer believes these to be biogenic!--><ref name=Seilacher1998>{{cite journal | author = Seilacher, A. | authorlink = Adolf Seilacher | coauthors = Bose, P.K.; 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 | url = http://sciencemag.org/cgi/content/abstract/282/5386/80 | accessdate = 2007-05-21 | pmid = 9756480 }}</ref> however their uneven width and tapering ends make a biological origin difficult to defend.<ref name=Budd2000>{{cite journal | author = Budd, G.E. | coauthors = Jensen, S. | year = 2000 | title = A critical reappraisal of the fossil record of the bilaterian phyla | journal = Biological Reviews | volume = 75 | issue = 02 | pages = 253–295 | doi = 10.1017/S000632310000548X | url = http://www.journals.cambridge.org/abstract_S000632310000548X | accessdate = 2007-06-27 }}</ref> The first evidence of burrowing which is widely accepted dates to the Ediacaran period, around {{Ma|570}}{{Verify source|date=April 2008}}. During this period, burrows are horizontal, or just below the surface. Such burrows must have been made by motile organisms with heads, which would probably have been [[bilateria|bilateran]] [[animal]]s.<ref>{{cite journal | 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 = http://books.google.co.uk/books?id=gUQMKiJOj64C&pg=PP1&ots=BkpdtmDml1&sig=ap0OD3JXuSkTVhJTSqQbT5uC2P8 | isbn = 0306440679 | publisher = Springer | accessdate = 2007-03-08 }}</ref> The burrows 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|Dzik, J|The Verdun Syndrome: simultaneous origin of protective armour and infaunal shelters at the Precambrian–Cambrian transition|405|414|30 }}</ref> The complex, efficient feeding traces common from the start of the ensuing Cambrian period are absent. Some Ediacaran fossils, especially discs, have been interpreted tentatively as trace fossils, but this hypothesis has not gained widespread acceptance. As well as burrows, some trace fossils have been found directly associated with an Ediacaran fossil. ''[[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. | coauthors = Malakhovskaya, Y.E. | year = 2002 | title = Giant Traces of Vendian Animals | journal = Doklady Earth Sciences (Doklady Akademii Nauk) | volume = 385 | issue = 6 | pages = 618–622 | issn = 1028-334X | language = Russian; English translation available | url = http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf | accessdate = 2007-05-10 }}</ref> the method of formation of these disconnected and overlapping fossils largely remains a mystery. The potential [[mollusc]] ''Kimberella'' is associated with scratch marks thought to have been formed by its [[radula]],<ref name=Martin2000>According to {{cite journal | author = Martin, M.W. | coauthors = Grazhdankin, D.V.; Bowring, S.A.; Evans, D.A.D.; Fedonkin, M.A.; 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 | doi = 10.1126/science.288.5467.841 | url = http://www.scienceonline.org/cgi/content/abstract/288/5467/841 | pmid = 10797002 }} For a more cynical<!--"doubting"?--> perspective see {{cite journal | author = Butterfield, N.J. | year = 2006 | title = Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale | journal = Bioessays | volume = 28 | issue = 12 | pages = 1161–6 | doi = 10.1002/bies.20507 | url = http://doi.wiley.com/10.1002/bies.20507 }}</ref> further traces from {{Ma|555}} appear to imply active crawling or burrowing activity.<ref name=Martin2000 /> As the Cambrian got underway, new forms of trace fossil appeared, including vertical burrows<ref>e.g. ''[[Diplocraterion]]'' and ''[[Skolithos]]''</ref> 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. | year = 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 | accessdate = 2007-09-09 }}</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 | doi = 10.1126/science.246.4928.339 | pmid = 17747916 }}</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 | number=1 | year=2003 | pages=219–228 | accessdate = 2007-04-21 | publisher=The Society for Integrative and Comparative Biology | doi = 10.1093/icb/43.1.219 <!--Retrieved from Yahoo! by DOI bot-->}}</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. | coauthors = 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 | issn = | doi = | url = http://pubs.nrc-cnrc.gc.ca/rp/rppdf/z01-211.pdf | accessdate = 2007-04-21 }} 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. The earliest arthropod trackways date to the Cambro-Ordovician,<ref name=MacNaughton2002>{{cite journal | author = MacNaughton, R.B. | coauthors = Cole, J.M.; Dalrymple, R.W.; Braddy, S.J.; Briggs, D.E.G.; 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 }}</ref> and trackways from the Ordovician [[Tumblagooda sandstone]] allow the behaviour of these organisms to be determined.<ref name=Trewin1995>{{cite journal | author = Trewin, N.H. | coauthors = McNamara, K.J. | year = 1995 | title = Arthropods invade the land: trace fossils and palaeoenvironments of the Tumblagooda Sandstone (? late Silurian) of Kalbarri, Western Australia | journal = Transactions of the Royal Society of Edinburgh: Earth Sciences | volume = 85 | pages = 177–210 }} See [[Tubmlagooda sandstone]] for discussion of Ordovician age.</ref> The enigmatic trace fossil ''[[Climactichnites]]'' may represent an earlier still terrestrial trace, perhaps made by a slug-like organism.{{Verify source|date=June 2008}} ==Common ichnogenera== [[Image:ThalassinoidesIsrael.JPG|thumb|''[[Thalassinoides]]'', burrows produced by crustaceans, from the Middle [[Jurassic]], [[Makhtesh]] Qatan, southern [[Israel]].]] *''[[Skolithos]]'': One well-known occurrence of Cambrian trace fossils from this period is the famous '[[Pipe Rock]]' of northwest [[Scotland]]. The 'pipes' that give the rock its name are closely packed straight tubes- which were presumably made by some kind of [[worm]]-like organism. The name given to this type of tube or burrow is ''Skolithos'', which may be 30 cm (12") in length and between 2 to 4 cm (0.8 to 1.6") in diameter. Such traces are known worldwide from sands and [[sandstone]]s deposited in shallow water environments, from the [[Cambrian]] period (542 to 488 m.y.a) onwards. * ''[[Chondrites]]'' are small branching burrows of the same diameter, which superficially resemble the roots of a plant. The most likely candidate for having constructed these burrows is a [[nematode]] (roundworm). ''Chondrites'' are found in marine sediments from the [[Cambrian]] period of the [[Paleozoic]] onwards. They are especially common in sediments which were deposited in reduced-oxygen environments. [[Image:Cruziana2.jpg|thumb|right|200px|''Cruziana'']] * ''[[Cruziana]]'' are excavation trace marks made on the sea floor which have a two-lobed structure with a central groove. The lobes are covered with scratch marks made by the legs of the excavating organism, usually a [[trilobite]] or allied arthropod and, in fact, several different types of trilobite have been discovered at the end of ''Cruziana'' trails{{Fact|date=February 2007}}. ''Cruziana'' are most common in marine sediments formed during the [[Paleozoic]] era, particularly in rocks from the [[Cambrian]] and [[Ordovician]] periods. Over 30 species of ''Cruziana'' have been identified. * ''[[Thalassinoides]]'' are burrows which occur parallel to the bedding plane of the rock and are extremely abundant in rocks, worldwide, from the [[Jurassic]] period onwards. They are repeatedly branched, with a slight swelling present at the junctions of the tubes. The burrows are cylindrical and vary from 2 to 5 cm (0.8" to 2") in diameter. ''Thalassinoides'' sometimes contain scratch marks, droppings or the bodily remains of the [[crustacean]]s which made them. * ''[[Asteriacites]]'' is the name given to the five-rayed fossils found in rocks and they record the resting place of [[starfish]] on the sea floor. ''Asteriacites'' are found in European and American rocks, from the [[Ordovician]] period onwards; and are numerous in rocks from the [[Jurassic]] period of [[Germany]]. * ''[[Rhizocorallium]]'' is a type of [[burrow]], the inclination of which is typically within 10° of the bedding planes of the sediment. These burrows can be very large, over a meter long in sediments that show good preservation, e.g. [[Jurassic]] rocks of the [[Yorkshire]] Coast (eastern [[United Kingdom]]), but the width is usually only up to 2 cm, restricted by the size of the organisms producing it. It is thought that they represent fodinichnia as the animal (probably a [[nematode]]) scoured the [[sediment]] for food. * ''[[Teichichnus]]'' has a distinctive form produced by the stacking of thin 'tongues' of [[sediment]], atop one another. They are again believed to be fodinichnia, with the organism adopting the habit of retracing the same route through varying heights of the sediment, which would allow it to avoid going over the same area. These 'tongues' are often quite sinuous, reflecting perhaps a more nutrient-poor environment in which the feeding animals had to cover a greater area of sediment, in order to acquire sufficient nourishment. * ''[[Protichnites]]'' consists of two rows of tracks and a linear depression between the two rows. The tracks are believed to have been made by the walking appendages of [[arthropod]]s. The linear depression is thought to be the result of a dragging tail. The structures bearing this name were typically made on the tidal flats of [[Paleozoic]] seas, but similar ones extend into the [[Cenozoic]]. * ''[[Climactichnites]]'' is the name given to trackways that usually consist of two parallel ridges separated by chevron-shaped raised cross bars. They somewhat resemble tire tracks, and are larger (typically about four inches wide) than most of the other trace fossils made by [[invertebrates]]. The tracks were produced on sandy tidal flats during late [[Cambrian]] time. While the identity of the animal is still conjectural, it may have been a large [[slug]]-like animal - its trackways produced as it crawled over and processed the wet sand to obtain food. ==Other notable trace fossils== Less ambiguous than the above ichnogenera, are the traces left behind by [[invertebrate]]s such as ''[[Hibbertopterus]]'', a giant "[[sea scorpion]]" or [[eurypterid]] of the early [[Paleozoic]] era. This marine [[arthropod]] produced a spectacular hibbertopteroid track preserved in Scotland.<ref>{{cite journal|author=Whyte, MA |year=2005) |title=Palaeoecology: A gigantic fossil arthropod trackway |journal=Nature|volume=438|pages=576 |doi=10.1038/438576a}}</ref> [[Bioerosion]] through time has produced a magnificent record of borings, gnawings, scratchings and scrapings on hard substrates. These trace fossils are usually divided into macroborings<ref>Wilson, M.A., 2007. Macroborings and the evolution of bioerosion, p. 356-367. In: Miller, W. III (ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, 611 pages.</ref> and microborings<ref>* Glaub, I., Golubic, S., Gektidis, M., Radtke, G. and Vogel, K., 2007. Microborings and microbial endoliths: geological implications. In: Miller III, W (ed) Trace fossils: concepts, problems, prospects. Elsevier, Amsterdam: pp. 368-381. * Glaub, I. and Vogel, K., 2004. The stratigraphic record of microborings. Fossils & Strata 51:126-135.</ref>. Bioerosion intensity and diversity is punctuated by two events. One is called the Ordovician Bioerosion Revolution (see Wilson & Palmer, 2006) and the other was in the Jurassic<ref> * Taylor, P.D. and Wilson, M.A., 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1-103.[http://www.wooster.edu/geology/Taylor%26Wilson2003.pdf]</ref>. For a comprehensive bibliography of the bioerosion literature, please see the External links below. The oldest types of [[tetrapod]] tail-and-foot prints date back to the latter [[Devonian]] period. These [[vertebrate]] impressions have been found in [[Ireland]], [[Scotland]], [[Pennsylvania]], and [[Australia]]. Important [[human evolution|human]] trace fossils are the [[Laetoli]] ([[Tanzania]]) footprints, imprinted in volcanic ash 3.7 million years ago ([[mya (unit)|mya]]) -- probably by an early [[Australopithecus]]. == Confusion with other types of fossils == Trace fossils should not be confused with body casts. The [[Ediacara]] biota, for instance, primarily comprises the casts of organisms in sediment. Early geologists gave the name 'fucoid' to a wide variety of markings they found on the bedding planes of [[sedimentary rocks]]. The earth scientists frequently misinterpreted these 'fucoid' marks as being the fossilized remains of [[seaweed]]. However, in more recent years, these markings have been studied with greater thoroughness. It is now apparent that the 'fucoids' and other markings have in fact been caused by a variety of plants and animals. As a result, these 'fucoid' markings are now termed trace fossils. [[Pseudofossil]]s, which are ''not'' true fossils, should also not be confused with ichnofossils, which are true indications of prehistoric life. <gallery> Image:FaringdonCobble.JPG|Numerous borings in a Cretaceous cobble, Faringdon, England; see Wilson (1986). Image:BoredEncrustedShell.JPG|Sponge borings and encrusters on a modern bivalve shell, North Carolina. Image:Helminthopsis01.JPG|''Helminthopsis'' ichnosp.; a trace fossil from the Logan Formation (Lower Carboniferous) of [[Wooster, Ohio]]. </gallery> == See also == {{commons|Category:Trace fossils}} * [[Bioerosion]] * [[Bird ichnology]] * [[Ichnite]] - fossilised footprints * [[Ichnofacies]] * [[Trace fossil classification]] == References == {{reflist|2}} {{Nofootnotes|date=April 2008}} * Bromley, R.G., 1970. Borings as trace fossils and ''Entobia cretacea'' Portlock as an example, p. 49-90. In: Crimes, T.P. and Harper, J.C. (eds.), Trace Fossils. Geological Journal Special Issue 3. * Bromley, R.G., 2004. A stratigraphy of marine bioerosion. In: The application of ichnology to palaeoenvironmental and stratigraphic analysis. (Ed. D. McIlroy), Geological Society of London Special Publications 228:455-481. * Palmer, T.J., 1982. Cambrian to Cretaceous changes in hardground communities. Lethaia 15:309-323. * Wilson, M.A., 1986. Coelobites and spatial refuges in a Lower Cretaceous cobble-dwelling hardground fauna. Palaeontology 29:691-703. * Wilson, M.A. and Palmer, T.J., 2006. Patterns and processes in the Ordovician Bioerosion Revolution. Ichnos 13: 109-112.[http://www.wooster.edu/geology/WilsonPalmer06.pdf] * Yochelson, E.L. and Fedonkin, M.A., 1993. Paleobiology of ''Climactichnites'', and Enigmatic Late Cambrian Fossil. Smithsonian Contributions to Paleobiology 74:1-74. == External links == * http://www.peripatus.gen.nz/paleontology/trafos.html * http://www.envs.emory.edu/ichnology/ * [http://www.wooster.edu/geology/Bioerosion/Bioerosion.html Bioerosion Website] at [[The College of Wooster]] * [http://www.wooster.edu/geology/bioerosion/BioerosionBiblio.pdf Comprehensive bioerosion bibliography compiled by Mark A. Wilson] [[Category:Trace fossils| ]] [[Category:Paleozoology]] [[Category:Bioindicators]] [[Category:Microbiology]] [[ca:Icnofòssil]] [[de:Palichnologie]] [[el:Βιοδηλωτικά ίχνη]] [[es:Icnofósil]] [[fr:Paléoichnologie]] [[nl:Sporenfossiel]] [[ja:生痕化石]] [[pl:Skamieniałość śladowa]]