Editing Living fossil (section)

==Characteristics==
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| image1 = Ginkgo huttoni 1.jpg
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| caption1 = 170 million-year-old fossil ''Ginkgo'' leaves
| caption2 = Living ''[[Ginkgo biloba]]'' plant
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Living fossils have two main characteristics, although some have a third:
# Living organisms that are members of a [[taxon]] that has remained  recognizable in the fossil record over an unusually long time span.
# They show little morphological divergence, whether from early members of the lineage, or among [[Extant taxon|extant species]]. 
# They tend to have little taxonomic diversity.<ref>{{cite book |last1=Eldridge |first1=Niles |last2=Stanley |first2=Steven |title=Living Fossils |date=1984 |publisher=Springer-Verlag |location=New York}}</ref>
The first two are required for recognition as a living fossil; some authors also require the third, others merely note it as a frequent trait.

Such criteria are neither well-defined nor clearly quantifiable, but modern methods for analyzing evolutionary dynamics can document the distinctive tempo of stasis.<ref>{{cite journal |last1=Butler |first1=M. |last2=King |first2=A. |title=Phylogenetic comparative analysis: A modeling approach for adaptive evolution |journal=The American Naturalist |date=2004 |volume=164 |issue=6 |pages=683–695 |doi=10.1086/426002 |pmid=29641928|s2cid=4795316 }}</ref><ref>{{cite journal |last1=Hansen |first1=T. |last2=Martins |first2=E. |title=Translating between microevolutionary process and macroevolutionary patterns: The correlation structure of interspecific data |journal=Evolution |date=1996 |volume=50 |issue=4 |pages=1404–1417 |doi=10.2307/2410878 |pmid=28565714 |jstor=2410878}}</ref><ref>{{cite journal |last1=Harmon |first1=L. |last2=Losos |first2=J. |last3=Davies |first3=T. |last4=Gillespie |first4=R. |last5=Gittleman |first5=J. |last6=Jennings |first6=W. |last7=Kozak |first7=K. |last8=McPeek |first8=M. |last9=Moreno-Roark |first9=F. |last10=Near |first10=T. |last11=Purvis |first11=A. |last12=Ricklefs |first12=R. |last13=Schluter |first13=D. |last14=Schulte |first14=J. |last15=Seehausen |first15=O. |last16=Sidlauskas |first16=B. |last17=Torres-Carvajal |first17=O. |last18=Weir |first18=J. |last19=Mooers |first19=A |display-authors=6 |title=Early bursts of body size and shape evolution are rare in comparative data |journal=Evolution |year=2010 |volume=64 |issue=8 |pages=2385–2396 |doi=10.1111/j.1558-5646.2010.01025.x |pmid=20455932|s2cid=17544335 }}</ref> Lineages that exhibit stasis over very short time scales are not considered living fossils; what is poorly-defined is the time scale over which the morphology must persist for that lineage to be recognized as a living fossil.

The term ''living fossil'' is much misunderstood in popular media in particular, in which it often is used meaninglessly. In professional literature the expression seldom appears and must be used with far more caution, although it has been used inconsistently.<ref>{{cite journal |vauthors=Nagalingum NS, Marshall CR, Quental TB, Rai HS, Little DP, Mathews S |title=Recent synchronous radiation of a living fossil |journal=Science |date=2011-11-11 |volume=334 |issue=6057 |pages=796–799 |doi=10.1126/science.1209926 |pmid=22021670 |bibcode=2011Sci...334..796N |s2cid=206535984 |publication-date=2011-10-20 <!-- e-Pub -->}}</ref><ref>{{cite report |author1=Cavin, Lionel |author2=Guinot, Guillaume |title=Coelacanths as "almost living fossils" |series=Perspective Article |date=13 August 2014 |doi=10.3389/fevo.2014.00049 |publisher=Département de Géologie et Paléontologie |department=Muséum d'Histoire Naturelle |location=Genève, Switzerland|doi-access=free }}</ref>

One example of a concept that could be confused with "living fossil" is that of a "[[Lazarus taxon]]", but the two are not equivalent; a Lazarus taxon (whether a single species or a [[Systematics|group of related species]]) is one that suddenly reappears, either in the fossil record or in nature, as if the fossil had "come to life again".<ref name=":2">{{cite journal |vauthors=Dawson MR, Marivaux L, Li CK, Beard KC, Métais G |title=Laonastes and the "Lazarus effect" in recent mammals |journal=Science |date=2006-03-10 |volume=311 |issue=5766 |pages=1456–1458|doi=10.1126/science.1124187 |pmid=16527978 |bibcode=2006Sci...311.1456D |s2cid=25506765}}</ref> In contrast to "Lazarus taxa", a living fossil in most senses is a species or lineage that has undergone exceptionally little change throughout a long fossil record, giving the impression that the extant taxon had remained identical through the entire fossil and modern period. Because of the mathematical inevitability of [[genetic drift]], though, the DNA of the modern species is necessarily different from that of its distant, similar-looking ancestor. They almost certainly would not be able to cross-reproduce, and are not the same species.<ref>{{cite web |date=6 Jul 2016 |url=https://www.theguardian.com/science/2016/jul/06/why-its-time-to-make-living-fossils-extinct |author=Mark Carnall |title=Let's make living fossils extinct |work=The Guardian}}</ref>

The average [[Beta diversity#Absolute species turnover|species turnover]] time, meaning the time between when a species first is established and when it finally disappears, varies widely among [[phylum (biology)|phyla]], but averages about 2–3{{nbsp}}million years.<ref>{{Cite book |last=Lawton |first=John H. |url=https://archive.org/details/extinctionrates00lawt/mode/2up?q=million |title=Extinction rates |last2=May |first2=Robert M. (Robert McCredie) |date=1995 |publisher=Oxford; New York : Oxford University Press |others=Internet Archive |isbn=978-0-19-854829-4}}</ref> A living taxon that had long been thought to be extinct could be called a Lazarus taxon once it was discovered to be still extant. A dramatic example was the order [[Coelacanthiformes]], of which the genus ''[[Latimeria]]'' was found to be extant in 1938. About that there is little debate – however, whether ''Latimeria'' resembles early members of its lineage sufficiently closely to be considered a living fossil as well as a Lazarus taxon has been denied by some authors in recent years.<ref name="Casane"/>

Coelacanths disappeared from the fossil record some 80{{nbsp}}million years ago (in the upper [[Cretaceous]] period) and, to the extent that they exhibit low rates of morphological evolution, extant species qualify as living fossils. It must be emphasised that this criterion reflects fossil evidence, and is totally independent of whether the taxa had been subject to selection at all, which all living populations continuously are, whether they remain genetically unchanged or not.<ref name="Yadav2009"/>

This apparent stasis, in turn, gives rise to a great deal of confusion – for one thing, the fossil record seldom preserves much more than the general morphology of a specimen. To determine much about its physiology is seldom possible; not even the most dramatic examples of living fossils can be expected to be without changes, no matter how persistently constant their fossils and the extant specimens might seem. To determine much about [[noncoding DNA]] is hardly ever possible, but even if a species were hypothetically unchanged in its physiology, it is to be expected from the very nature of the reproductive processes, that its non-functional [[genomics|genomic]] changes would continue at more-or-less standard rates. Hence, a fossil lineage with apparently constant morphology need not imply equally constant physiology, and certainly neither implies any cessation of the basic evolutionary processes such as natural selection, nor reduction in the usual rate of change of the noncoding DNA.<ref name="Yadav2009">{{cite book |author=Yadav, P.R. |title=Understanding Palaeontology |date=1 January 2009 |publisher=Discovery Publishing House |isbn=978-81-8356-477-9 |pages=4 ff |url=https://books.google.com/books?id=zAWNWNWcQ08C&pg=PP4}}</ref>

Some living fossils are taxa that were known from palaeontological fossils before living representatives were discovered. The most famous examples of this are:
* [[Coelacanth]]iform fishes (2 species)
* ''Metasequoia'', the [[dawn redwood]] discovered in a remote Chinese valley (1 species)
* [[Glypheoidea|Glypheoid lobsters]] (2 species)
* [[Mymarommatidae|Mymarommatid wasps]] (10 species)
* [[Eomeropidae|Eomeropid scorpionflies]] (1 species)
* [[Jurodidae|Jurodid beetles]] (1 species)
* [[Echinothurioida|Soft sea urchins]] (59 species)

All the above include taxa that originally were described as fossils but now are known to include still-extant species.

Other examples of living fossils are single living species that have no close living relatives, but are survivors of large and widespread groups in the fossil record. For example:
* ''[[Ginkgo biloba]]''
* ''[[Syntexis libocedrii]]'', the cedar wood wasp
* [[Dinoflagellates]] (typified on coccoid [[dinocysts]]: occasionally calcareous cell remnants)

All of these were described from fossils before later being found alive.<ref name="Caloperosum">{{cite journal |last1=Montresor |first1=M. |last2=Janofske |first2=D. |last3=Willems |first3=H. |year=1997 |title=The cyst-theca relationship in ''Calciodinellum operosum'' emend. (Peridiniales, Dinophyceae) and a new approach for the study of calcareous cysts |journal=Journal of Phycology |volume=33 |issue=1 |pages=122–131 |doi=10.1111/j.0022-3646.1997.00122.x|bibcode=1997JPcgy..33..122M |s2cid=84169394 }}</ref><ref name="Postricari">{{cite journal |last1=Gu |first1=H. |last2=Kirsch |first2=M. |last3=Zinßmeister |first3=C. |last4=Söhner |first4=S. |last5=Meier |first5=K.J.S. |last6=Liu |first6=T. |last7=Gottschling |first7=M. |year=2013 |title=Waking the dead: Morphological and molecular characterization of extant †''Posoniella tricarinelloides'' (Thoracosphaeraceae, Dinophyceae) |journal=Protist |volume=164 |issue=5 |pages=583–597 |doi=10.1016/j.protis.2013.06.001 |pmid=23850812}}</ref><ref name="dx.doi.org">{{cite journal |last1=Mertens |first1=K.N. |last2=Takano |first2=Y. |last3=Head |first3=M.J. |last4=Matsuoka |first4=K. |year=2014 |title=Living fossils in the Indo-Pacific warm pool: A refuge for thermophilic dinoflagellates during glaciations |journal=Geology |volume=42 |issue=6 |pages=531–534 |doi=10.1130/G35456.1|bibcode=2014Geo....42..531M }}</ref>

The fact that a living fossil is a surviving representative of an archaic lineage does not imply that it must retain all the "primitive" features ([[Plesiomorphy|plesiomorphies]]) of its ancestral lineage. Although it is common to say that living fossils exhibit "morphological stasis", stasis, in the scientific literature, does not mean that any species is strictly identical to its ancestor, much less remote ancestors.

Some living fossils are relicts of formerly diverse and morphologically varied lineages, but not all survivors of ancient lineages necessarily are regarded as living fossils. See for example the uniquely and highly autapomorphic [[oxpecker]]s, which appear to be the only survivors of an ancient lineage related to [[starling]]s and [[mockingbird]]s.<ref name="Zuccon">{{cite journal |author1=Zuccon, Dario |author2=Cibois, Anne |author3=Pasquet, Eric |author4=Ericson, Per G.P. |year=2006 |title=Nuclear and mitochondrial sequence data reveal the major lineages of starlings, mynas and related taxa |journal=[[Molecular Phylogenetics and Evolution]] |volume=41 |issue=2 |pages=333–344 |doi=10.1016/j.ympev.2006.05.007 |pmid=16806992 |bibcode=2006MolPE..41..333Z |url=http://www.nrm.se/download/18.25ba04a21296cc434f980001039/Zuccon+et+al+2006+Starlings+MPEV.pdf |access-date=2011-02-20 |archive-date=2021-10-25 |archive-url=https://web.archive.org/web/20211025143403/https://www.nrm.se/download/18.25ba04a21296cc434f980001039/Zuccon+et+al+2006+Starlings+MPEV.pdf |url-status=dead }}</ref>