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A living fossil is a deprecated term for an
extant taxon Neontology is a part of biology that, in contrast to paleontology, studies and 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) w ...
that phenotypically resembles related
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
. 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 Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene va ...
would inevitably change its chromosomal structure. Living fossils exhibit stasis (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 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. The term is currently deprecated among paleontologists and evolutionary biologists.


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''; : 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 name and ...
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 species. # They tend to have little taxonomic diversity. 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. 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 Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, is the change in the Allele frequency, frequency of an existing gene variant (allele) in a population due to random chance. Genetic drift may cause gene va ...
, 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 2–3million 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 Coelacanths ( ) are an ancient group of Sarcopterygii, lobe-finned fish (Sarcopterygii) in the Class (biology), class Actinistia. As sarcopterygians, they are more closely related to lungfish and tetrapods (the terrestrial vertebrates including ...
, 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 80million years ago (in the upper
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...
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. 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'' * '' 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. 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''), 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 (epistemology), justification, or argument by their reliance on experience. knowledge is independent from any ...
'' 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 Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...
in his '' On the Origin of Species'' from 1859, when discussing '' Ornithorhynchus'' (the platypus) and '' Lepidosiren'' (the South American lungfish):


Other definitions


Long-enduring

A living taxon that lived through a large portion of geologic time. The
Australian 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''), 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 100million years old. Modern Queensland lungfish have existed as a species for almost 30million years. The contemporary nurse shark has existed for more than 112million 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 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'') are not real living fossils. In the case of ''Triops cancriformis'' (living from the
Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...
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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
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 Biogeography is the study of the species distribution, distribution of species and ecosystems in geography, geographic space and through evolutionary history of life, geological time. Organisms and biological community (ecology), communities o ...
strongly suggests that oxpeckers originated in eastern
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
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 analyses used to classify
tuatara The tuatara (''Sphenodon punctatus'') is a species of reptile endemic to New Zealand. Despite its close resemblance to lizards, it is actually the only extant member of a distinct lineage, the previously highly diverse order Rhynchocephal ...
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".


Bacteria

*
Cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...
– the oldest living fossils, emerging 3.5 billion years ago. They exist as single bacteria or in the form of
stromatolite Stromatolites ( ) or stromatoliths () are layered Sedimentary rock, sedimentary formation of rocks, formations (microbialite) that are created mainly by Photosynthesis, photosynthetic microorganisms such as cyanobacteria, sulfate-reducing micr ...
s, layered rocks produced by colonies of cyanobacteria.


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 kingdom ...
''Tergestiella adriatica''.


Plants

*
Moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
* Pteridophytes ** Horsetails – ''Equisetum'' ** Lycopods ** Tree ferns and ferns * Gymnosperms ** Conifers ***'' Agathis'' – kauri in New Zealand, Australia and the Pacific and almasiga in the Philippines *** ''
Araucaria araucana ''Araucaria araucana'', commonly called the monkey puzzle tree, monkey tail tree, pewen, pehuen pine or piñonero, is an evergreen tree belonging to the family Araucariaceae and growing to a trunk diameter of and a height of . It is native to ...
'' – the monkey puzzle tree (as well as other extant '' Araucaria'' species) *** '' Metasequoia'' – dawn redwood (Cupressaceae; related to '' Sequoia'' and '' Sequoiadendron'') *** ''
Sciadopitys ''Sciadopitys'', commonly called umbrella pines, is a genus of a unique conifers now endemic to Japan. The sole living member of the family Sciadopityaceae is '' Sciadopitys verticillata'', a living fossil. The oldest fossils of ''Sciadopitys'' ...
'' – a unique conifer endemic to Japan known in the fossil record for about 230 million years. *** '' Taiwania cryptomerioides'' – one of the largest tree species in Asia. *** '' Wollemia'' tree (''
Araucariaceae Araucariaceae is a Family (biology), family of conifers with three living Genus, genera, ''Araucaria'', ''Agathis'', and ''Wollemia''. While the family's native distribution is now largely confined to the Southern Hemisphere, except for a few spe ...
'' – a borderline example, related to '' Agathis'' and '' Araucaria'') ** Cycads – although this has been challenged by multiple lines of evidence ** ''
Ginkgo ''Ginkgo'' is a genus of non-flowering seed plants, assigned to the gymnosperms. The scientific name is also used as the English common name. The order to which the genus belongs, Ginkgoales, first appeared in the Permian, , and ''Ginkgo'' is n ...
'' tree (Ginkgoaceae) ** '' Welwitschia'' *
Angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit ...
s ** ''
Amborella ''Amborella'' is a monotypic genus of understory shrubs or small trees endemic to the main island, Grande Terre, of New Caledonia in the southwest Pacific Ocean. The genus is the only member of the family Amborellaceae and the order Amborella ...
'' – a plant from New Caledonia, possibly closest to base of the flowering plants ** '' Magnolia –'' a genus whose form is little changed since the earliest days of flowering plant evolution in the Cretaceous and possibly earli

** '' 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. ** '' Sassafras'' – many fossils of sassafras are known from the late cretaceous through the late pleistocene. ** ''
Platanus ''Platanus'' ( ) is a genus consisting of a small number of tree species native to the Northern Hemisphere. They are the sole living members of the family Platanaceae. All mature members of ''Platanus'' are tall, reaching in height. The type ...
'' Sycamore fossils are very abundant throughout the northern hemisphere with several extinct species. Sycamore leaves and fruits are quite common in plant fossils. Sycamores exhibit many primitive features as well such their exfoliating bark which is a result of a lack of elasticity. Platanus Occidentalis fossils are known from the pliocene and the pleistocene in North America. ** '' Nyssa'' Blackgum fossils go way back to the late cretaceous period. Many extinct species are recorded as well. ** ''
Liriodendron ''Liriodendron'' () is a genus of two species of characteristically large trees, deciduous tree, deciduous over most of their populations, in the magnolia family (biology), family (Magnoliaceae). These trees are widely known by the common name ...
'' Fossils from the cretaceous and the tertiary period are found with many extinct species. Tulip Trees at one point were present in Europe during the cretaceous and the early paleocene. Liriodendron Tulipifera fossils dating from the pliocene and pleistocene were discovered at the chowan formation in North Carolina. ** '' Liquidambar'' Sweetgums appeared during the mid-late cretaceous and several extinct species are found throughout Asia, Europe and North America. The genus was once widespread in Europe and Asia especially during the miocene. The American Sweetgum is a living fossil itself since fossil specimens dating from the miocene, pliocene and pleistocene were discovered in the eastern United States


Fungi

* '' Neolecta''


Animals

;Vertebrates: * Mammals ** Aardvark (''Orycteropus afer'') ** Amami rabbit (''Pentalagus furnessi'') ** Nesolagus (''Asian striped rabbits'') ** Chevrotain (''Tragulidae'') ** Chousingha (''Tetracerus quadricornis'') ** Elephant shrew (Macroscelidea) ** Giant panda (''Ailuropoda melanoleuca'') ** Baiji (''Lipotes vexillifer) (One living species)'' ** Ganges river dolphin (''Platanista gangetica)'' ** Indus river dolphin (''Platanista minor)'' ** Hawaiian monk seal (''Neomonachus schauinslandi'') **
Koala The koala (''Phascolarctos cinereus''), sometimes inaccurately called the koala bear, is an arboreal herbivorous marsupial native to Australia. It is the only Extant taxon, extant representative of the Family (biology), family ''Phascolar ...
(''Phascolarctos cinereus'') ** Laotian rock rat (''Laonastes aenigmamus'') ** Monito del monte (''Dromiciops gliroides'') ** Monotremes (the platypus and echidna) **
Mountain beaver The mountain beaver (''Aplodontia rufa'')Other names include boomer, mountain boomer, ground bear, giant mole, gehalis, sewellel, suwellel, showhurll, showtl, and showte, as well as a number of other Native American terms. "Mountain beaver" is a ...
(''Aplodontia rufa'') ** Okapi (''Okapia johnstoni'') ** Opossums (''Didelphidae'') ** Clouded leopard (''Neofelis nebulousa'') ** Bush dog (''Speothos venaticus'') **
Maned wolf The maned wolf (''Chrysocyon brachyurus'') is a large canine of South America. It is found in Argentina, Brazil, Bolivia, Peru, and Paraguay, and is almost extinct in Uruguay. Its markings resemble those of a red fox, but it is neither a fox nor ...
(''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 (''Dinomys branickii'') ** Rhinoceroses (Rhinocerotidae) **
Tapirs Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a Suidae, pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South America, South and Centr ...
(Tapiridae) * Birds **
Pelican Pelicans (genus ''Pelecanus'') are a genus of large water birds that make up the family Pelecanidae. They are characterized by a long beak and a large throat pouch used for catching prey and draining water from the scooped-up contents before ...
s (''Pelecanus'') – form has been virtually unchanged since the
Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
, 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 Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...
. Distinct lineage of Passeriformes. ** Broad-billed sapayoa (''Sapayoa aenigma'') – One living species. Distinct lineage of Tyranni. ** Bearded reedling (''Panurus biarmicus'') – One living species. Distinct lineage of Passerida or Sylvioidea. ** Picathartes (rockfowls) ** Coliiformes (mousebirds) – 6 living species in 2 genera. Distinct lineage of
Neoaves Neoaves is a clade that consists of all modern bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard ...
. ** Hoatzin (''Ophisthocomus hoazin'') – One living species. Distinct lineage of
Neoaves Neoaves is a clade that consists of all modern bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard ...
. ** Magpie goose (''Anseranas semipalmata'') – One living species. Distinct lineage of Anseriformes. ** Sandhill crane (''Antigone canadensis'') – Oldest living species. ** Seriema (''Cariamidae'') – 2 living species. Distinct lineage of Cariamae. ** Tinamiformes (tinamous) 50 living species. Distinct lineage of
Palaeognathae Palaeognathae (; ) is an infraclass of birds, called paleognaths or palaeognaths, within the class Aves of the clade Archosauria. It is one of the two extant taxon, extant infraclasses of birds, the other being Neognathae, both of which form Neo ...
. * Reptiles ** Crocodilia ( crocodiles, gavials, caimans and alligators) ** Pig-nosed turtle (''Carettochelys insculpta'') ** Hickatee (''Dermatemys mawii'') ** Snapping turtle ('' Chelydridae'') family **
Tuatara The tuatara (''Sphenodon punctatus'') is a species of reptile endemic to New Zealand. Despite its close resemblance to lizards, it is actually the only extant member of a distinct lineage, the previously highly diverse order Rhynchocephal ...
('' Sphenodon punctatus'' and '' Sphenodon guntheri'') ** Asian forest tortoise ('' Manouria emys'') ** Impressed tortoise ('' Manouria impressa'') ** Sunbeam snake ('' Xenopeltis hainanensis'' and '' Xenopeltis unicolor'') ** Leatherback sea turtle (''Dermochelys coriacea'') * Amphibians ** Giant salamanders ('' Cryptobranchus'' and '' Andrias'') ** Hula painted frog ('' Latonia nigriventer'') ** Purple frog (''Nasikabatrachus sahyadrensis'') * Jawless fish **
Hagfish Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that h ...
(''Myxinidae'') family ** Lamprey (''Petromyzontiformes'') * Bony fish ** Arowana and
arapaima The arapaima, pirarucu, or paiche is any large species of bonytongue in the genus ''Arapaima'' native to the Amazon Basin, Amazon and Essequibo River, Essequibo basins of South America. ''Arapaima'' is the type genus of the subfamily Arapaiminae ...
(''Osteoglossidae'') ** Bowfin (''Amia calva'') ** Coelacanth (the lobed-finned ''Latimeria menadoensis'' and ''Latimeria chalumnae'') ** Gar (''Lepisosteidae'') ** Queensland lungfish (''Neoceratodus fosteri'') ** African lungfish (''Protopterus sp.'') ** Sturgeons and paddlefish ( Acipenseriformes) ** Bichir (family ''Polypteridae'') ** '' Protanguilla palau'' ** Mudskipper (''Oxudercinae'') * Sharks ** Blind shark (''Brachaelurus waddi'') ** Bullhead shark (''Heterodontus sp.'') ** Cow shark (sixgill sharks and relatives) (''Hexanchidae'') ** Elephant shark (''Callorhinchus milii'') ** Frilled shark (''Chlamydoselachus sp.'') ** Goblin shark (''Mitsukurina owstoni'') ** Gulper shark (''Centrophorus sp.'') ;Invertebrates: * Insects ** '' Cyatta abscondita ''(most recent common relative of '' Atta'' and '' Acromyrmex'' ant genera) ** 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 Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
) ** Mymarommatid wasps (10 living species in genus ''Palaeomymar'') ** Nevrorthidae (3 species-poor genera) ** '' Nothomyrmecia'' (known as the 'dinosaur ant') ** '' Notiothauma reedi'' (a scorpionfly relative) ** Orussidae (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'' (a jurodid
beetle Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
) ** '' Syntexis libocedrii'' (Anaxyelidae cedar wood wasp) ** '' Tricholepidion gertschi'' (silverfish with nearest relatives in Eocene) * Crustaceans ** Glypheidea (2 living species: ''Neoglyphea inopinata'' and ''Laurentaeglyphea neocaledonica'') ** Stomatopods (mantis shrimp) ** Polychelida (deep sea blind lobster) ** '' Triopsidae'' (also known as tadpole shrimp;
notostraca The order Notostraca, containing the single family Triopsidae, is a group of crustaceans known as tadpole shrimp or shield shrimp. The two genera, ''Triops'' and ''Lepidurus'', are considered living fossils, with similar forms having existed since ...
n crustaceans) * Molluscs ** Nautilina (e.g., '' Nautilus pompilius'') ** '' Neopilina'' – Monoplacophoran ** Slit snail (e.g., '' Entemnotrochus rumphii'') ** '' Vampyroteuthis infernalis'' – the vampire squid ** Pleurocerid snails * Other invertebrates ** Crinoids ** Horseshoe crabs (only 4 living species of the class Xiphosura, family Limulidae) ** '' Lingula anatina'' (an inarticulate
brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...
) ** Liphistiidae (trapdoor spiders) **
Onychophora Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, ''Peripatus''), is a phylum of el ...
ns (velvet worms) ** '' Rhabdopleura'' (a hemichordate) ** '' Valdiviathyris quenstedti'' (a craniforman brachiopod) ** '' Paleodictyon nodosum'' (unknown)


See also

* Relict (biology) * Breeding back * Lazarus taxon


Notes

Baiji is not officially classified as extinct, but instead critically endangered, possibly extinct and has the unofficial status of functional extinction.


References


External links


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