Trace fossil classification: Difference between revisions

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{{Short description|Systems for grouping fossilised evidence of biological activity}}

[[Trace fossil]]s are [[Biological classification|classified]] in various ways for different purposes. Traces can be classified [[#Taxonomic classification|taxonomically]] (by morphology), [[#Ethologic classification|ethologically]] (by behavior), and [[#Toponomic classification|toponomically]], that is, according to their relationship to the surrounding sedimentary layers. Outside of special cases, phylogenetic classification of trace fossils is unsatisfactory because the makers of most trace fossils are unknown.

{{redirect|Ichnos|the Tony Oxley album|Ichnos (album)}}

[[Trace fossil]]s are [[Biological classification|classified]] in various ways for different purposes. Traces can be classified [[#Taxonomic classification|taxonomically]] (by morphology), [[#Ethologic classification|ethologically]] (by behavior), and [[#Toponomic classification|toponomically]], that is, according to their relationship to the surrounding sedimentary layers. OutsideExcept ofin the specialrare cases, phylogeneticwhere classificationthe original maker of a trace fossilsfossil iscan unsatisfactorybe becauseidentified thewith makersconfidence, ofphylogenetic mostclassification of trace fossils areis an unreasonable unknownproposition.

==Taxonomic classification== <!--intro links here-->

The '''taxonomic classification of trace fossils''' parallels the taxonomic classification of [[organism]]s under the [[International Code of Zoological Nomenclature]]. In [[trace fossil]] nomenclature a [[Latin]] [[binomial nomenclature|binomial name]] is used, just as in [[animal]] and [[plant]] [[Taxonomy (biology)|taxonomy]], with a [[genus]] and [[specific name (zoology)|specific epithet]]. However, the [[binomial names]] are not linked to an organism, but rather just a trace fossil. This is due to the rarity of association between a trace fossil and a specific organism or group of organisms. Trace fossils are therefore included in an ''[[ichnotaxon]]'' separate from [[Linnaean taxonomy]]. When referring to trace fossils, the terms ''ichnogenus'' and ''ichnospecies'' parallel genus and [[species]] respectively.

The most promising cases of phylogenetic classification are those in which similar trace fossils show details complex enough to deduce the makers, such as [[bryozoan]] [[bioerosion|borings]], large [[trilobite]] trace fossils such as ''[[Cruziana]]'', and [[vertebrate]] [[footprints]]. However, most trace fossils lack sufficiently complex details to allow such classification.

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===The Seilacherian System===

[[File:BoredEncrustedShell.JPG|thumb|Sponge borings (''[[Entobia]]'') and encrusters on a modern bivalve shell, North Carolina; an example of ''Domichnia''.]]

[[Adolf Seilacher]] was the first to propose a broadly accepted [[ethology|ethological]] basis for trace fossil classification.<ref>{{cite journal |last=Seilacher, |first=A. (|year=1953) |title=Studien zur paläontologiePaläontologie: 1. Über die methodenMethoden der palichnologie.Palichnologie |journal=Neues Jahrbuch furfür Geologie und Paläontologie, |series=Abhandlungen |volume=96: 421-452.|pages=421–452 }}</ref><ref name="Seilacher, A 1964">{{cite journal |last=Seilacher, |first=A. (|year=1964) |title=Sedimentological classification and nomenclature of trace fossils. |journal=Sedimentology |volume=3: 253|pages=253–256 |doi=10.1111/j.1365-2563091.1964.tb00464.x }}</ref> He recognized that most trace fossils are created by [[animal]]s in one of five main behavioural activities, and named them accordingly:

* ''Cubichnia'' are the traces of organisms left on the surface of a soft [[sediment]]. This behaviour may simply be resting as in the case of a [[starfish]], but might also evidence the hiding place of [[prey]], or even the ambush position of a [[predator]].

* ''Domichnia'' are dwelling structures that reflect the life positions of organisms, for example the subsurface [[burrow]]s or [[bioerosion|borings]] of [[suspension feeder]]s, and are perhaps the most common of the established ethological classes.

* '''''Cubichnia''''' are the traces of organisms left on the surface of a soft [[sediment]]. This behaviour may simply be resting as in the case of a [[starfish]], but might also evidence the hiding place of [[prey]], or even the ambush position of a [[predator]].

* '''''Domichnia''''' are dwelling structures that reflect the life positions of organisms, for example the subsurface [[burrow]]s or [[bioerosion|borings]] of [[suspension feeder]]s, and are perhaps the most common of the established ethological classes.

* ''[[Fodinichnia]]'' are feeding traces which are formed as a result of organisms disturbing the sediment in their search for food. They are normally created by [[deposit feeder]]s as they tunnel through soft sediments, usually producing a 3D structure.

* '''''Pascichnia''''' are a different type of feeding trace for which the trophic guild responsible are [[grazing|grazer]]s. They create 2D features as they scour the surface of a hard or soft [[Substrate (biology)|substrate]] in order to obtain [[nutriment]].

* '''''Repichnia''''' are locomotory tracks that show evidence of organisms moving from one station to another, usually in a near-straight to slightly curved line. Most of the very few traces to be verifiably assigned to a specific organism are in this category, such as various [[arthropod]] and [[vertebrate]] trackways.<ref>{{cite journal |last=Seilacher, |first=A. (|year=1967) |title=Bathymetry of trace fossils. |journal=Marine Geology |volume=5: 413|issue= 5–6|pages=413–428 |doi=10.1016/0025-4283227(67)90051-5 |bibcode=1967MGeol...5..413S }}</ref>

* ''Pascichnia'' are a different type of feeding trace for which the trophic guild responsible are [[grazing|grazer]]s. They create 2D features as they scour the surface of a hard or soft [[Substrate (biology)|substrate]] in order to obtain [[nutriment]].

* ''Repichnia'' are locomotory tracks that show evidence of organisms moving from one station to another, usually in a near-straight to slightly curved line. Most of the very few traces to be verifiably assigned to a specific organism are in this category, such as various [[arthropod]] and [[vertebrate]] trackways.<ref>Seilacher, A (1967) Bathymetry of trace fossils. Marine Geology 5: 413-428.</ref>

===Other ethological classes===

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Since the inception of behavioural categorization, several other ethological classes have been suggested and accepted, as follows:

* ''Aedificichnia'':<ref>{{cite journal |last1=Bown, TM;|first1=T. M. |last2=Ratcliffe, BC|first2=B. (C. |year=1988) |title=The origin of ''Chubutolithes'' Ihering, ichnofossils from the Eocene and Oligocene of Chubut province, Argentina. |journal=Journal of Paleontology |volume=62 |issue=2 |pages=163–167 |doi=10.1017/S0022336000029802 |bibcode=1988JPal...62..163B |s2cid=20261299 |url=http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1136&context=entomologypapers 163|url-167.access=subscription }}</ref> evidence of organisms building structures outside of the [[infauna]]l realm, such as [[termite]] mounds or [[wasp]] nests.

* ''Agrichnia'':<ref>Ekdale, AA; Bromley, RG; Pemberton, SG (1984) Ichnology: Trace fossils in sedimentology and stratigraphy. Society of Economic Paleontologists and Mineralogists Short Course, no 15, 317 pp.</ref> so called "gardening traces", which are systematic burrow networks designed to capture migrating [[meiofauna]] or perhaps even to culture [[bacteria]]. The organism would have continually inspected this burrow system to prey on any smaller organisms that strayed into it.

* ''Calichnia'':<ref>Genise, JF & Bown, TM (1991) New Miocene scarabaeid and hymenopterous nests and Early Miocene (Santacrucian) palaeoenvironments, Patagonian Argentina. Ichnos, 3: 107–117.</ref> structures that were created by organisms specifically for [[Reproduction|breeding]] purposes, e.g. [[bee]] cells.

* ''Equilibrichnia'':<ref>Bromley, RG (1990) Trace fossils: biology and taphonomy. Unwin Hyman Ltd, London, 280 pp.</ref> burrows within the sediment that show evidence for organisms' responses to variations in sedimentation rate (i.e. the burrow moves upwards to avoid burial, or downwards to avoid exposure). Typically this evidence will be in the form of [[spreiten]], which are small laminations in the sediment that reflect previous positions the organisms were in.

* ''[[Fugichnia]]'':<ref>Simpson, S (1975) The morphological classification of trace fossils. In Frey, RW (ed.) The study of trace fossils. New York, Springer-Verlag, pp 39-54.</ref> "escape traces" that are formed as a result of organisms' attempts to escape burial in sudden high-sedimentation events like [[turbidity current]]s. The burrows are often marked with chevron patterns showing the upward direction the organisms were tunnelling.

* ''Praedichnia'':<ref>Ekdale, AA (1985) Palaeoecology of the marine endobenthos. Palaeogeography, Palaeoecology, Palaeoclimatology 50: 63-81.</ref> trace fossils that show evidence of [[predator]]y behaviour, such as the drill holes ([[bioerosion|borings]]) left in [[Animal shellExoskeleton|shell]]s by [[carnivorous]] [[gastropod]]s, or more dramatically, the bite marks found on some [[vertebrate]] [[bone]]s.

* ''Praedichnia'':<ref>Ekdale, AA (1985) Palaeoecology of the marine endobenthos. Palaeogeography, Palaeoecology, Palaeoclimatology 50: 63-81.</ref> trace fossils that show evidence of [[predator]]y behaviour, such as the drill holes ([[bioerosion|borings]]) left in [[Animal shell|shell]]s by [[carnivorous]] [[gastropod]]s, or more dramatically, the bite marks found on some [[vertebrate]] [[bone]]s.

Over the years several other behavioural groups have been proposed, but in general they have been quickly discarded by the ichnological community. Some of the failed proposals are listed below, with a brief description.

* ''Chemichnia'': a type of agrichnia applied specifically to those instances of [[bacteria]]l harvesting.

* ''Cecidoichnia'': a plant trace in which a gall is left on the plant as a result of interaction with animals, bacteria, or other plants.

* ''Corrosichnia'': traces that are left by plant [[root]]s as a result of their [[corrosive]] action on the sediments.

* ''Cursichnia'': a subgroup of the repichnia, created by a crawling or walking habit.

* ''Fixichnia'': traces left by [[Sessility (zoology)|sessile]] organisms that anchored themselves to a hard substrate.

* ''Mordichnia'': a praedichnial subgroup that shows evidence of the prey's death as a result of the attack.

* ''Natichnia'': a type of repichnia caused by disturbances to a soft sediment by a swimming organism, e.g. a [[benthic]] [[fish]].

* ''Polychresichnia'': traces that show an origin in the combination of two or more established trace-producing behaviours, e.g. domichnia that served as the feeding position of the organisms.

* ''Sphenoichnia'': a plant trace created by the [[bioturbation]]al action of roots.

* ''Taphichnia'': fugichnia in which the organism failed to escape and was buried, often resulting in its body fossil being found in association with the trace.

* ''Volichnia'': traces that show the position a flying organism (usually an insect) landed on a soft sediment.

Fixichnia<ref>{{cite journal |last1=Gibert, JM|first1=J. M. de, |last2=Domènech, |first2=R. & |last3=Martinell, |first3=J. (|year=2004) |title=An ethological framework for animal bioerosion trace fossils upon mineral substrates with proposal of new class, fixichnia. |journal=Lethaia |volume=37 (|issue=4): 429-437|pages=429–437 |doi=10.1080/00241160410002144 |bibcode=2004Letha..37..429G }}</ref> is perhaps the group with the most weight as a candidate for the next accepted ethological class, being not fully described by any of the eleven currently accepted categories. There is also potential for the three plant traces (cecidoichnia, corrosichnia and sphenoichnia) to gain recognition in coming years, with little attention having been paid to them since their proposal.<ref>{{cite journal |last=Mikuláš, |first=R. (|year=1999) |title=Notes on the concept of plant trace fossils related to plant-generated sedimentary structures. |journal=Věštník Českého geologickéhoGeologického ústavu |volume=74: 39-42.|issue=1 |pages=39–42 }}</ref>

==Toponomic classification==

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* ''Endichnia'' are those traces that are found wholly within the casting medium, and therefore can only have been made by an infaunal organism.

* ''Epichnia'' are found on the tops of the strata of origin, being those ridges and grooves that were formed by benthic organisms or infaunal burrows that have been exposed by [[erosion]].

* ''Exichnia'' are traces that are made of material that is different from the surrounding medium, having either been actively filled by an organism or eroded out and re-covered by an alien sediment.

* ''Hypichnia'' are ridges and grooves found on the soles of the beds of origin at their interfaces with other [[stratum|strata]], representing the opposite of epichnia.

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==History==

Early paleontologists originally classified many burrow fossils as the remains of marine [[algae]], as is apparent in ichnogenera named with the ''-phycus'' suffix. [[Alfred Gabriel Nathorst]] and Joseph F. James both controversially challenged this incorrect classification, suggesting the reinterpretation of many "algae" as marine invertebrate trace fossils.<ref name="TreatiseSupp1">{{Cite book|isbn=9780813730271|title= Miscellanea: Supplement 1, Trace Fossils and Problematica | last1= Häntzschel | first1= Walter |authorlink=Walter Häntzschel |editor1-last = Moore | editor1-first= Raymond C. | year= 1975 | publisher= Geological Society of America | series= Treatise on Invertebrate Paleontology}}</ref>

Several attempts to classify trace fossils have been made throughout the history of paleontology. In 1844, [[Edward Hitchcock]] proposed two [[order (biology)|orders]]: ''Apodichnites'', including footless trails, and ''Polypodichnites'', including trails of organisms with more than four feet.<ref name="TreatiseSupp1">< /ref>

==See also==

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==External links==

* [https://web.archive.org/web/20090416063931/http://www.peripatus.gen.nz/paleontology/trafos.html "Trace Fossils" by Kristian Saether & Christopher Clowes]

[[Category:Trace fossils|Classification ]]

[[Category:Biological classification]]

[[Category:Classification systems]]

[[Category:Zoological nomenclature]]