A living fossil is an

extant taxon Neontology is a part of biology that, in contrast to paleontology, deals with living (or, more generally, '' recent'') organisms. It is the study of extant taxa (singular: extant taxon): taxa (such as species, genera and families) with member ...

that cosmetically resembles related species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living fossils commonly are of species-poor lineages, but they need not be. While the body plan of a living fossil remains superficially similar, it is never the same species as the remote relatives it resembles, because genetic drift would inevitably change its chromosomal structure. Living fossils exhibit

stasis Stasis (from Greek στάσις "a standing still") may refer to: * A state in stability theory, in which all forces are equal and opposing, therefore they cancel out each other * Stasis (political history), a period of civil war within an ancient ...

(also called "bradytely") over geologically long time scales. Popular literature may wrongly claim that a "living fossil" has undergone no significant evolution since fossil times, with practically no

molecular evolution Molecular evolution is the process of change in the sequence composition of cellular molecules such as DNA, RNA, and proteins across generations. The field of molecular evolution uses principles of evolutionary biology and population genet ...

or morphological changes. Scientific investigations have repeatedly discredited such claims. The minimal superficial changes to living fossils are mistakenly declared as an absence of evolution, but they are examples of stabilizing selection, which is an evolutionary process—and perhaps the dominant process of morphological evolution.

Characteristics

Living fossils have two main characteristics, although some have a third: # Living organisms that are members of a

taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...

that has remained recognisable 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 species Neontology is a part of biology that, in contrast to paleontology, deals with living (or, more generally, ''recent'') organisms. It is the study of extant taxa (singular: extant taxon): taxa (such as species, genera and families) with members sti ...

. # They tend to have little taxonomic diversity. The first two are required for recognition as a ''living fossil'' status; 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. 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. 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 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". 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. The average species turnover time, meaning the time between when a species first is established and when it finally disappears, varies widely among

phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phy ...

, but averages about 2–3 million years. 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 The coelacanths ( ) are fish belonging to the order Actinistia that includes two extant species in the genus ''Latimeria'': the West Indian Ocean coelacanth (''Latimeria chalumnae''), primarily found near the Comoro Islands off the east coast ...

, 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. Coelacanths disappeared from the fossil record some 80 million years ago (upper

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

) 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. 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 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. Some living fossils are taxa that were known from palaeontological fossils before living representatives were discovered. The most famous examples of this are: * Coelacanthiform fishes (2 species) * ''Metasequoia'', the dawn redwood discovered in a remote Chinese valley (1 species) * glypheoid lobsters (2 species) * mymarommatid wasps (10 species) * eomeropid scorpionflies (1 species) * jurodid beetles (1 species) * 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 ''Ginkgo biloba'', commonly known as ginkgo or gingko ( ), also known as the maidenhair tree, is a species of tree native to China. It is the last living species in the order Ginkgoales, which first appeared over 290 million years ago. Fossils ...

'' * '' Syntexis libocedrii'', the cedar wood wasp *

Dinoflagellates The dinoflagellates ( Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates ...

(typified on coccoid dinocysts: occasionally calcareous cell remnants) All of these were described from fossils before later being found alive. 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 ( 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 oxpeckers, which appear to be the only survivors of an ancient lineage related to starlings and mockingbirds.

Evolution and living fossils

The term ''living fossil'' is usually reserved for species or larger clades that are exceptional for their lack of morphological diversity and their exceptional conservatism, and several hypotheses could explain morphological stasis on a geologically long time-scale. Early analyses of evolutionary rates emphasized the persistence of a taxon rather than rates of evolutionary change. Contemporary studies instead analyze rates and modes of phenotypic evolution, but most have focused on clades that are thought to be adaptive radiations rather than on those thought to be living fossils. Thus, very little is presently known about the evolutionary mechanisms that produce living fossils or how common they might be. Some recent studies have documented exceptionally low rates of ecological and phenotypic evolution despite rapid speciation. This has been termed a "non-adaptive radiation" referring to diversification not accompanied by adaptation into various significantly different niches. Such radiations are explanation for groups that are morphologically conservative. Persistent adaptation within an adaptive zone is a common explanation for morphological stasis. The subject of very low evolutionary rates, however, has received much less attention in the recent literature than that of high rates Living fossils are not expected to exhibit exceptionally low rates of molecular evolution, and some studies have shown that they do not. For example, on tadpole shrimp (''

Triops ''Triops'' is a genus of small crustaceans in the order Notostraca (tadpole shrimp). The long-lasting resting eggs of several species of ''Triops'' are commonly sold in kits as a pet. The animals hatch upon contact with fresh water. Most adult-st ...

''), one article notes, "Our work shows that organisms with conservative body plans are constantly radiating, and presumably, adapting to novel conditions.... I would favor retiring the term ‘living fossil’ altogether, as it is generally misleading." Some scientists instead prefer a new term stabilomorph, being defined as "an effect of a specific formula of adaptative strategy among organisms whose taxonomic status does not exceed genus-level. A high effectiveness of adaptation significantly reduces the need for differentiated phenotypic variants in response to environmental changes and provides for long-term evolutionary success." The question posed by several recent studies pointed out that the morphological conservatism of coelacanths is not supported by paleontological data. In addition, it was shown recently that studies concluding that a slow rate of molecular evolution is linked to morphological conservatism in coelacanths are biased by the ''

a priori ("from the earlier") and ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. knowledge is independent from current ex ...

'' hypothesis that these species are ‘living fossils’. Accordingly, the genome stasis hypothesis is challenged by the recent finding that the genome of the two extant coelacanth species ''L. chalumnae'' and ''L. menadoensis'' contain multiple species-specific insertions, indicating transposable element recent activity and contribution to post-speciation genome divergence. Such studies, however, challenge only a genome stasis hypothesis, not the hypothesis of exceptionally low rates of phenotypic evolution.

History

The term was coined by

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended ...

in his ''

On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...

'' from 1859, when discussing ''

Ornithorhynchus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypi ...

'' (the platypus) and ''

Lepidosiren The South American lungfish (''Lepidosiren paradoxa'') is the single species of lungfish found in swamps and slow-moving waters of the Amazon, Paraguay, and lower Paraná River basins in South America. Notable as an obligate air-breather, it is t ...

'' (the South American lungfish):

Other definitions

Long-enduring

A living taxon that lived through a large portion of geologic time. The Australian lungfish (''Neoceratodus fosteri''), also known as the Queensland lungfish, is an example of an organism that meets this criterion. Fossils identical to modern specimens have been dated at over 100 million years old. Modern Queensland lungfish have existed as a species for almost 30 million years. The contemporary nurse shark has existed for more than 112 million years, making this species one of the oldest, if not actually the oldest extant vertebrate species.

Resembles ancient species

A living taxon morphologically and/or

physiologically Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical a ...

resembling a fossil taxon through a large portion of geologic time (morphological stasis).

Retains many ancient traits

A living taxon with many characteristics believed to be primitive. This is a more neutral definition. However, it does not make it clear whether the taxon is truly old, or it simply has many plesiomorphies. Note that, as mentioned above, the converse may hold for true living fossil taxa; that is, they may possess a great many derived features ( autapomorphies), and not be particularly "primitive" in appearance.

Relict population

Any one of the above three definitions, but also with a relict distribution in refuges. Some paleontologists believe that living fossils with large distributions (such as ''

Triops cancriformis ''Triops cancriformis'', European tadpole shrimp or tadpole shrimp, is a species of tadpole shrimp found in Europe to the Middle East and India. Due to habitat destruction, many populations have recently been lost across its European range, ...

'') are not real living fossils. In the case of ''Triops cancriformis'' (living from the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

until now), the Triassic specimens lost most of their appendages (mostly only carapaces remain), and they have not been thoroughly examined since 1938.

Low diversity

Any of the first three definitions, but the clade also has a low taxonomic diversity (low diversity lineages). Oxpeckers are morphologically somewhat similar to starlings due to shared plesiomorphies, but are uniquely adapted to feed on parasites and blood of large land mammals, which has always obscured their relationships. This lineage forms part of a radiation that includes Sturnidae and Mimidae, but appears to be the most ancient of these groups. Biogeography strongly suggests that oxpeckers originated in eastern

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

and only later arrived in Africa, where they now have a relict distribution. The two living species thus seem to represent an entirely extinct and (as Passerida go) rather ancient lineage, as certainly as this can be said in the absence of actual fossils. The latter is probably due to the fact that the oxpecker lineage never occurred in areas where conditions were good for fossilization of small bird bones, but of course, fossils of ancestral oxpeckers may one day turn up enabling this theory to be tested.

Operational definition

An operational definition was proposed in 2017, where a 'living fossil' lineage has a slow rate of evolution and occurs close to the middle of morphological variation (the centroid of morphospace) among related taxa (i.e. a species is morphologically conservative among relatives). The scientific accuracy of the

morphometric Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are c ...

analyses used to classify tuatara as a living fossil under this definition have been criticised however, which prompted a rebuttal from the original authors.

Examples

Some of these are informally known as "living fossils". Ginkgo Stamm

Bacteria

* Cyanobacteria - the oldest living fossils, emerging 3.5 billion years ago. They exist as single bacteria but are most often pictured as stromatolites, artificial rocks produced by cyanobacteria waste.

Protists

* The dinoflagellate †''Calciodinellum operosum''. * The dinoflagellate †''Dapsilidinium pastielsii''. * The dinoflagellate †''Posoniella tricarinelloides''. * The

coccolithophore Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the king ...

''Tergestiella adriatica''.

Plants

* Moss * Pteridophytes ** Horsetails – ''Equisetum'' ** Lycopods ** Tree ferns and ferns *

Gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...

s ** Conifers ***'' Agathis'' – kauri in New Zealand, Australia and the Pacific and almasiga in the Philippines *** '' Araucaria araucana'' – the monkey puzzle tree (as well as other extant '' Araucaria'' species) *** ''

Metasequoia ''Metasequoia'', or dawn redwoods, is a genus of fast-growing deciduous trees, one of three species of conifers known as redwoods. The living species ''Metasequoia glyptostroboides'' is native to Lichuan county in Hubei province, China. Althou ...

'' – dawn redwood (Cupressaceae; related to '' Sequoia'' and '' Sequoiadendron'') *** '' Sciadopitys'' – a unique conifer endemic to Japan known in the fossil record for about 230 million years. *** ''

Taiwania cryptomerioides ''Taiwania'', with the single living species ''Taiwania cryptomerioides'', is a large coniferous tree in the cypress family Cupressaceae. Etymology ''Taiwania'' means 'from Taiwan', while ''Cryptomerioides'' means 'resembling ''Cryptomeria''.Gle ...

'' – one of the largest tree species in Asia. *** '' Wollemia'' tree ('' Araucariaceae'' – a borderline example, related to '' Agathis'' and '' Araucaria'') **

Cycad Cycads are seed plants that typically have a stout and woody (ligneous) trunk with a crown of large, hard, stiff, evergreen and (usually) pinnate leaves. The species are dioecious, that is, individual plants of a species are either male o ...

s ** '' Ginkgo'' tree (Ginkgoaceae) ** '' Welwitschia'' * Angiosperms ** '' Amborella'' – a plant from New Caledonia, possibly closest to base of the

flowering plants Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants t ...

** '' Trapa'' - water caltrops, seeds, and leaves of numerous extinct species are known all the way back to the Cretaceous. ** '' Nelumbo'' - several species of lotus flower are known exclusively from fossils dating back to the Cretaceous.

Fungi

* ''

Neolecta ''Neolecta'' is a genus of ascomycetous fungi that have fruiting bodies in the shape of unbranched to lobed bright yellowish, orangish to pale yellow-green colored, club-shaped, smooth, fleshy columns up to about 7 cm tall. The species shar ...

Animals

;Vertebrates: Hoatzins in Ecuador

* Mammals ** Aardvark (''Orycteropus afer'') ** Amami rabbit (''Pentalagus furnessi'') **

Nesolagus ''Nesolagus'' is a genus of rabbits containing three species of striped rabbit: the Annamite striped rabbit, the Sumatran striped rabbit, and the extinct species ''N. sinensis''. Overall there is very little known about the genus as a whole, mo ...

(''Asian striped rabbits'') **

Chevrotain Chevrotains, or mouse-deer, are small even-toed ungulates that make up the family Tragulidae, the only extant members of the infraorder Tragulina. The 10 extant species are placed in three genera, but several species also are known only f ...

(''Tragulidae'') ** Chousingha (''Tetracerus quadricornis'') ** Elephant shrew (Macroscelidea) ** Laotian rock rat (''Laonastes aenigmamus'') ** Monito del monte (''Dromiciops gliroides'') ** Monotremes (the

platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or mono ...

and echidna) **

Mountain beaver The mountain beaver (''Aplodontia rufa'')Other names include mountain boomer, ground bear, giant mole, gehalis, lesser sasquatch, sewellel, suwellel, showhurll, showtl, and showte, as well as a number of Chinookan and other Native American terms ...

(''Aplodontia rufa'') ** Okapi (''Okapia johnstoni'') ** Sumatran rhinoceros ('' Dicerorhinus sumatrensis'') ** Opossums (''Didelphidae'') ** Clouded leopard (''Neofelis nebulousa'') ** Capybara (''Hydrochoerus hydrochaeris'') **

Bush dog The bush dog (''Speothos venaticus'') is a canine found in Central and South America. In spite of its extensive range, it is very rare in most areas except in Suriname, Guyana and Peru; it was first identified by Peter Wilhelm Lund from foss ...

(''Speothos venaticus'') ** Maned wolf (''Chrysocyon brachyurus'') ** Red panda (''Ailurus fulgens'') ** Solenodon ('' Solenodon cubanus'' and '' Solenodon paradoxus'') ** Shrew opossum (''Caenolestidae'') ** Spectacled bear (''Tremarctos ornatus'') ** False killer whale (''Pseudorca crassidens'') ** Pygmy right whale (''Caperea marginata'') **

Pacarana The pacarana (''Dinomys branickii'') is a rare and slow-moving hystricognath rodent indigenous to South America. Native Tupi people call it the ''pacarana'' (false paca) because it is superficially similar to the paca, a different rodent which is ...

(''Dinomys branickii'') * Birds ** Pelicans (''Pelecanus'') –

form Form is the shape, visual appearance, or configuration of an object. In a wider sense, the form is the way something happens. Form also refers to: *Form (document), a document (printed or electronic) with spaces in which to write or enter data * ...

has been virtually unchanged since the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

, and is noted to have been even more conserved across the Cenozoic than that of crocodiles. ** Acanthisittidae (New Zealand "wrens") – 2 living species, a few more recently extinct. Distinct lineage of Passeriformes. ** Broad-billed sapayoa (''Sapayoa aenigma'') – One living species. Distinct lineage of

Tyranni The Tyranni (suboscines) are a suborder of passerine birds that includes more than 1,000 species, the large majority of which are South American. It is named after the type genus ''Tyrannus''. These have a different anatomy of the syrinx m ...

. **

Bearded reedling The bearded reedling (''Panurus biarmicus'') is a small, sexually dimorphic reed-bed passerine bird. It is frequently known as the bearded tit, due to some similarities to the long-tailed tit, or the bearded parrotbill. It is the only species ...

(''Panurus biarmicus'') – One living species. Distinct lineage of Passerida or Sylvioidea. **

Picathartes The picathartes, rockfowl, or bald crows are a small genus of two passerine bird species forming the family Picathartidae found in the rain-forests of tropical west and central Africa. They have unfeathered heads, and feed on insects and inverte ...

(rockfowls) ** Coliiformes (mousebirds) – 6 living species in 2 genera. Distinct lineage of Neoaves. ** Hoatzin (''Ophisthocomus hoazin'') – One living species. Distinct lineage of Neoaves. ** Magpie goose (''Anseranas semipalmata'') – One living species. Distinct lineage of Anseriformes. ** Seriema (''Cariamidae'') – 2 living species. Distinct lineage of Cariamae. ** Tinamiformes (tinamous) 50 living species. Distinct lineage of Palaeognathae. * Reptiles **

Crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

( crocodiles, gavials, caimans and

alligator An alligator is a large reptile in the Crocodilia order in the genus ''Alligator'' of the family Alligatoridae. The two extant species are the American alligator (''A. mississippiensis'') and the Chinese alligator (''A. sinensis''). Additional ...

s) ** Pig-nosed turtle (''Carettochelys insculpta'') ** Hickatee (''Dermatemys mawii'') **

Snapping turtle The Chelydridae is a family of turtles that has seven extinct and two extant genera. The extant genera are the snapping turtles, ''Chelydra'' and ''Macrochelys''. Both are endemic to the Western Hemisphere. The extinct genera are ''Acheronte ...

('' Chelydridae'') family ** Tuatara ('' Sphenodon punctatus'' and ''

Sphenodon guntheri Tuatara (''Sphenodon punctatus'') are reptiles endemic to New Zealand. Despite their close resemblance to lizards, they are part of a distinct lineage, the order Rhynchocephalia. The name ''tuatara'' is derived from the Māori language and m ...

'') **

Asian forest tortoise The Asian forest tortoise (''Manouria emys''), also known commonly as the Mountain tortoise, is a species of tortoise in the family Testudinidae. The species is endemic to Southeast Asia. It is believed to be among the most primitive of living ...

('' Manouria emys'') ** Impressed tortoise ('' Manouria impressa'') ** Sunbeam snake ('' Xenopeltis hainanensis'' and '' Xenopeltis unicolor'') ** Leatherback sea turtle (''Dermochelys coriacea'') * Amphibians ** Giant salamanders ('' Cryptobranchus'' and ''

Andrias ''Andrias'' is a genus of giant salamanders. It includes the largest salamanders in the world, with ''A. japonicus'' reaching a length of , and ''A. sligoi'' reaching . While extant species are only known from East Asia, several extinct specie ...

'') **

Hula painted frog The Hula painted frog (''Latonia nigriventer'') is an amphibian and the only living member of the genus '' Latonia,'' which was originally described from several fossil species from the Oligocene to Early Pleistocene of Europe. The Hula painted f ...

('' Latonia nigriventer'') ** Purple frog (''Nasikabatrachus sahyadrensis'') Nautilus profile

* Jawless fish ** Hagfish (''Myxinidae'') family ** Lamprey (''Petromyzontiformes'') * Bony fish ** Arowana and arapaima (''Osteoglossidae'') ** Bowfin (''Amia calva'') ** Coelacanth (the lobed-finned ''Latimeria menadoensis'' and ''Latimeria chalumnae'') ** Gar (''Lepisosteidae'') **

Queensland lungfish The Australian lungfish (''Neoceratodus forsteri''), also known as the Queensland lungfish, Burnett salmon and barramunda, is the only surviving member of the family Neoceratodontidae. It is one of only six extant lungfish species in the world. ...

(''Neoceratodus fosteri'') ** African lungfish (''Protopterus sp.'') ** Sturgeons and

paddlefish Paddlefish (family Polyodontidae) are a family of ray-finned fish belonging to order Acipenseriformes, and one of two living groups of the order alongside sturgeons (Acipenseridae). They are distinguished from other fish by their titular elong ...

(

Acipenseriformes Acipenseriformes is an order of basal ray-finned fishes that includes living and fossil sturgeons and paddlefishes (Acipenseroidei), as well as the extinct families Chondrosteidae and Peipiaosteidae. They are the second earliest diver ...

) ** Bichir (family ''Polypteridae'') ** '' Protanguilla palau'' ** Mudskipper (''Oxudercinae'') * Sharks ** Blind shark (''Brachaelurus waddi'') **

Bullhead shark The bullhead sharks are a small order (Heterodontiformes ) of modern sharks ( Neoselachii). The nine living species are placed in a single genus, ''Heterodontus'', in the family Heterodontidae. All are relatively small, with the largest species ...

(''Heterodontus sp.'') ** Cow shark (sixgill sharks and relatives) (''Hexanchidae'') **

Elephant shark The Australian ghostshark (''Callorhinchus milii'') is a cartilaginous fish (Chondrichthyes) belonging to the subclass Holocephali (chimaera). Sharks, rays and skates are the other members of the cartilaginous fish group and are grouped under the ...

(''Callorhinchus milii'') ** Frilled shark (''Chlamydoselachus sp.'') **

Goblin shark The goblin shark (''Mitsukurina owstoni'') is a rare species of deep-sea shark. Sometimes called a "living fossil", it is the only extant representative of the family Mitsukurinidae, a lineage some 125 million years old. This pink-skinned anim ...

(''Mitsukurina owstoni'') ** Gulper shark (''Centrophorus sp.'') ;Invertebrates: * Insects ** Helorid wasps (1 living genus, 11 extinct genera) ** Mantophasmatodea (gladiators; a few living species) ** Meropeidae (3 living species, 4 extinct) ** '' Micromalthus debilis'' (a

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

) ** Mymarommatid wasps (10 living species in genus ''Palaeomymar'') ** Nevrorthidae (3 species-poor genera) ** ''

Nothomyrmecia ''Nothomyrmecia'', also known as the dinosaur ant or dawn ant, is an extremely rare genus of ants consisting of a single species, ''Nothomyrmecia macrops''. These ants live in South Australia, nesting in old-growth mallee woodland and ''Eucalyp ...

'' (known as the 'dinosaur ant') ** '' Notiothauma reedi'' (a scorpionfly relative) **

Orussidae The Orussidae or the parasitic wood wasps represent a small family of sawflies ("Symphyta"). Currently, about 93 extant and four fossil species are known. They take a key position in phylogenetic analyses of Hymenoptera, because they form the sis ...

(parasitic wood wasps; about 70 living species in 16 genera) ** Peloridiidae (peloridiid bugs; fewer than 30 living species in 13 genera) ** Rhinorhipid beetles (1 living species, Triassic origin) ** Rotoitid wasps (2 living species, 14 extinct) ** ''

Sikhotealinia zhiltzovae ''Sikhotealinia'' is a genus of beetle containing a single species, ''Sikhotealinia zhiltzovae'', which is the only living representative of the family Jurodidae. It was discovered in the Sikhote-Alin mountains in Outer Manchuria. This "living f ...

'' (a jurodid

) ** '' Syntexis libocedrii'' (Anaxyelidae cedar wood wasp) ** ''

Cyatta abscondita ''Cyatta'' is a genus of ant in the subfamily Myrmicinae containing the single species ''Cyatta abscondita''. It is considered the most recent ancestor of all fungus-farming ants and a living fossil. Etymology ''Cyatta'' is a neologism constru ...

''(most recent common relative of '' Atta'' and ''

Acromyrmex ''Acromyrmex'' is a genus of New World ants of the subfamily Myrmicinae. This genus is found in South America and parts of Central America and the Caribbean Islands, and contains 33 known species. Commonly known as "leafcutter ants" they compris ...

'' ant genera) * Crustaceans ** Glypheoidea (2 living species: ''Neoglyphea inopinata'' and ''Laurentaeglyphea neocaledonica'') ** Stomatopods (mantis shrimp) ** ''

'' (also known as tadpole shrimp; a notostracan

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

) * Molluscs ** Nautilina (e.g., ''

Nautilus pompilius The chambered nautilus (''Nautilus pompilius''), also called the pearly nautilus, is the best-known species of nautilus. The shell, when cut away, reveals a lining of lustrous nacre and displays a nearly perfect equiangular spiral, although it ...

'') ** '' Neopilina'' -

Monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell inhabiting deep sea environments . Extant representatives were not recognized as such until 1952; previously they were known only from ...

n ** Slit snail (e.g., ''

Entemnotrochus rumphii ''Entemnotrochus rumphii'', common name the Rumphius' slit shell, is a species of large sea snail with gills and an operculum, a marine gastropod mollusk in the family Pleurotomariidae, the slit snails.Bouchet, P. (2011). Entemnotrochus rumphii ...

'') ** ''

Vampyroteuthis infernalis The vampire squid (''Vampyroteuthis infernalis'', lit. 'vampire squid from hell') is a small cephalopod found throughout temperate and tropical oceans in extreme deep sea conditions. The vampire squid uses its bioluminescent organs and its uniqu ...

'' – the vampire squid * Other invertebrates ** Crinoids **

Horseshoe crab Horseshoe crabs are marine and brackish water arthropods of the family Limulidae and the only living members of the order Xiphosura. Despite their name, they are not true crabs or crustaceans: they are chelicerates, most closely related to ar ...

s (only 4 living species of the class Xiphosura, family Limulidae) ** '' Lingula anatina'' (an inarticulate brachiopod) ** Liphistiidae (trapdoor spiders) ** Onychophorans (velvet worms) ** '' Rhabdopleura'' (a hemichordate) ** '' Valdiviathyris quenstedti'' (a craniforman brachiopod) ** ''

Paleodictyon nodosum ''Paleodictyon nodosum'' is a living creature thought to produce a certain form of burrow nearly identical to ''Paleodictyon'' fossils. The modern burrows were found around mid-ocean ridge systems in the Pacific and Atlantic Oceans. Although scie ...

'' (unknown)

References

External links

MyTriops introduces ''Triops'' as living fossils
{{Authority control Evolutionary biology concepts Extinction Fossils