Lungfish are freshwater vertebrates belonging to the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Dipnoi. Lungfish are best known for retaining ancestral characteristics within the

Osteichthyes Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilage ...

, including the ability to breathe air, and ancestral structures within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Lungfish represent the closest living relatives of the

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...

s. Today there are only six known species of lungfish, living in

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

, and

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

. The fossil record shows that lungfish were abundant since 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 period ...

. While

vicariance Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

would suggest this represents an ancient distribution limited to the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

supercontinent

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

, the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

record suggests advanced lungfish had a widespread freshwater distribution and the current distribution of modern lungfish species reflects

extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

of many lineages subsequent to the breakup of Pangaea,

and

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pan ...

. Lungfish have historically been referred to as salamanderfish, but this term more often refers to '' Lepidogalaxias salamandroides''.

Anatomy and morphology

All lungfish demonstrate an uninterrupted cartilaginous

notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...

and an extensively developed palatal dentition.

Basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

(" primitive") lungfish groups may retain marginal teeth and an ossified braincase, but derived lungfish groups, including all modern species, show a significant reduction in the marginal bones and a cartilaginous braincase. The bones of the

skull roof The skull roof, or the roofing bones of the skull, are a set of bones covering the brain, eyes and nostrils in bony fishes and all land-living vertebrates. The bones are derived from dermal bone and are part of the dermatocranium. In comparati ...

in primitive lungfish are covered in a

mineralized tissue Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Typically these tissues form a protective shield or structural support. Bone, mollusc shells, deep sea sponge ''Euplectella'' species, radiolarians, diato ...

called

cosmine Cosmine is a spongy, bony material that makes up the dentine-like layers in the scales of the lobe-finned fishes of the class Sarcopterygii. Fish scales that include layers of cosmine are known as cosmoid scales. Description As traditionally des ...

, but in post-

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

lungfishes, the skull roof lies beneath the skin and the cosmine covering is lost. All modern lungfish show significant reductions and fusions of the bones of the skull roof, and the specific bones of the skull roof show no

homology Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor * Sequence homology, biological homology between DNA, RNA, or protein sequences *Homologous chrom ...

to the skull roof bones of

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

es or tetrapods. During the breeding season, the

South American lungfish 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 ...

develops a pair of feathery appendages that are actually highly modified pelvic fins. These fins are thought to improve gas exchange around the fish's eggs in its nest. Through

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

, lungfishes have evolved internal nostrils similar to the tetrapods'

choana The choanae (singular choana), posterior nasal apertures or internal nostrils are two openings found at the back of the nasal passage between the nasal cavity and the throat in tetrapods, including humans and other mammals (as well as crocodilia ...

, and a brain with certain similarities to the

Lissamphibia The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relatives), ...

n brain (except for the Queensland lungfish, which branched off in its own direction about 277 million years ago and has a brain resembling that of the '' latimeria''). The dentition of lungfish is different from that of any other

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

group. " Odontodes" on the palate and lower jaws develop in a series of rows to form a fan-shaped occlusion surface. These odontodes then wear to form a uniform crushing surface. In several groups, including the modern

lepidosireniformes Lev Berg Lev Semyonovich Berg, also known as Leo S. Berg (russian: Лев Семёнович Берг; 14 March 1876 – 24 December 1950) was a leading Russian geographer, biologist and ichthyologist who served as President of the Soviet Geogra ...

, these ridges have been modified to form occluding blades. The modern lungfishes have a number of larval features, which suggest paedomorphosis. They also demonstrate the largest

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

among the vertebrates. Modern lungfish all have an elongate body with fleshy, paired pectoral and

pelvic The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

fins and a single unpaired

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

replacing the dorsal, caudal and anal fins of most fishes.

Lungs

Lungfish have a highly specialized

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

. They have a distinct feature in that their lungs are connected to the larynx and pharynx without a trachea. While other species of fish can breathe air using modified, vascularized

gas bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their current water depth w ...

s, these bladders are usually simple sacs, devoid of complex internal structure. In contrast, the lungs of lungfish are subdivided into numerous smaller air sacs, maximizing the surface area available for gas exchange. Most extant lungfish species have two lungs, with the exception of the Australian lungfish, which has only one. The lungs of lungfish are

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

to the lungs of

s. As in tetrapods and bichirs, the lungs extend from the ventral surface of the

esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...

and gut.

Perfusion of water

Of extant lungfish, only the Australian lungfish can breathe through its gills without needing air from its lungs. In other species, the gills are too atrophied to allow for adequate

gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...

. When a lungfish is obtaining

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

from its gills, its circulatory system is configured similarly to the common fish. The spiral valve of the conus arteriosus is open, the bypass arterioles of the third and fourth gill arches (which do not actually have gills) are shut, the second, fifth and sixth gill arch arterioles are open, the ductus arteriosus branching off the sixth arteriole is open, and the pulmonary arteries are closed. As the water passes through the gills, the lungfish uses a buccal pump. Flow through the mouth and gills is unidirectional. Blood flow through the secondary lamellae is countercurrent to the water, maintaining a more constant concentration gradient.

Perfusion of air

When breathing air, the spiral valve of the conus arteriosus closes (minimizing the mixing of oxygenated and deoxygenated blood), the third and fourth gill arches open, the second and fifth gill arches close (minimizing the possible loss of the oxygen obtained in the lungs through the gills), the sixth arteriole's ductus arteriosus is closed, and the pulmonary arteries open. Importantly, during air breathing, the sixth gill is still used in respiration; deoxygenated blood loses some of its carbon dioxide as it passes through the gill before reaching the lung. This is because carbon dioxide is more soluble in water. Air flow through the mouth is tidal, and through the lungs it is bidirectional and observes "uniform pool" diffusion of oxygen.

Ecology and life history

Lungfish are omnivorous, feeding on fish,

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...

mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...

amphibian Amphibians are tetrapod, four-limbed and ectothermic vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terres ...

s and plant matter. They have an

intestinal spiral valve A spiral valve or scroll valve is the corkscrew-shaped lower portion of the intestine of some sharks, Acipenseriformes ( sturgeon and paddlefish), rays, skates, bichirs, Lepisosteiformes (gars), and lungfishes. A modification of the ileum, th ...

rather than a true stomach. African and South American lungfish are capable of surviving seasonal drying out of their habitats by burrowing into mud and estivating throughout the dry season. Changes in

physiology 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 ...

allow it to slow its

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

to as little as one sixtieth of the normal metabolic rate, and protein waste is converted from

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

to less-toxic

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...

(normally, lungfish excrete nitrogenous waste as ammonia directly into the water). Burrowing is seen in at least one group of fossil lungfish, the

Gnathorhizidae The Gnathorhizidae are an extinct family of lungfish that lived from the late Carboniferous until the middle Triassic. Gnathorhizid fossils have been found in North America, Madagascar, Australia, and possibly Eastern Europe and South Africa. T ...

. Lungfish can be extremely long-lived. A

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. ...

at the Shedd Aquarium in

Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

was part of the permanent live collection from 1933 to 2017 after a previous residence at the Sydney Aquarium; at perhaps 90 years old, it was euthanized following a decline in health consistent with old age. A primitive Australian fish living in a San Francisco museum is believed to be the oldest living aquarium fish in the world. Methuselah is a four-foot-long (1.2-meter) Australian lungfish, weighing around 40 lb (18.1 kg).

Evolution

About 420 million years ago, during the

, the last common ancestor of both lungfish and the

s split into two separate evolutionary linages, with the ancestor of the extant coelacanths diverging a little earlier from a

sarcopterygian Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includi ...

progenitor. The fossil of

Youngolepis ''Youngolepis'' is a genus of prehistoric lobe-finned fish which lived during the Early Devonian period (Lochkovian to Pragian stages, about 407-416 million years ago). Fossils of ''Y. praecursor'' have been found in the Xitun Formation of China ...

from about 415 million years ago already show significant modification of their jaws and jaw muscles towards the specialized lungfish feeding mechanism. '' Diabolepis'', a 400 million year old lungfish, is the oldest known unmistakingly durophagous vertebrate, and shows that the lungfishes had adapted to a diet including hard-shelled prey very early in their evolution. The transition could have taken as little as 7 million years. It is worth noting that, despite the name "lungfish", fish evolved lungs before lungfish, or even lobe-finned fish. The common ancestor of lobe-finned and

had lungs, but in most surviving branches of ray-finned fish these evolved into

swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled Organ (anatomy), organ that contributes to the ability of many bony fish (but not cartilaginous fish) to control their buoyancy, and thus to stay at their curren ...

s used for flotation, instead of breathing. Some, like the bichirs, do retain their lungs, and several other traits that appear to have been common to lobe-finned and ray-finned fish. While the coelacanth shares some traits with the tetrapods (reptiles, amphibians, birds and mammals), the lungfish have other tetrapod traits which are absent in the coelacanth. Evidence suggests that the tetrapods are related more closely to lungfish than to coelacanths.

Extant lungfish

The

, ''Neoceratodus forsteri'', is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

to Australia. Fossil records of this group date back 380 million years, around the time when the

higher vertebrate Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are distingu ...

classes were beginning to evolve. Fossils of lungfish belonging to the genus ''Neoceratodus'' have been uncovered in northern

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

, indicating that the Queensland lungfish has existed in Australia for at least 100 million years, making it a

living fossil A living fossil is an extant taxon 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 fossi ...

and one of the oldest living vertebrate genera on the planet. It is the most primitive surviving member of the ancient air-breathing lungfish (Dipnoi) lineages. The five other freshwater lungfish species,

four 4 (four) is a number, numeral and digit. It is the natural number following 3 and preceding 5. It is the smallest semiprime and composite number, and is considered unlucky in many East Asian cultures. In mathematics Four is the smallest c ...

in Africa and

one 1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...

in South America, are very different morphologically to ''N. forsteri''. The Queensland lungfish can live for several days out of the water if it is kept moist, but will not survive total water depletion, unlike its African counterparts. F de Castelnau-poissonsPl50

The

, ''Lepidosiren paradoxa'', is the single species of lungfish found in

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

s and slow-moving waters of the

Amazon Amazon most often refers to: * Amazons, a tribe of female warriors in Greek mythology * Amazon rainforest, a rainforest covering most of the Amazon basin * Amazon River, in South America * Amazon (company), an American multinational technology c ...

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

, and lower

Paraná River The Paraná River ( es, Río Paraná, links=no , pt, Rio Paraná, gn, Ysyry Parana) is a river in south-central South America, running through Brazil, Paraguay, and Argentina for some ."Parana River". Encyclopædia Britannica. Encyclopædia Br ...

basins Basin may refer to: Geography and geology * Depression (geology) ** Back-arc basin, a submarine feature associated with island arcs and subduction zones ** Debris basin, designed to prevent damage from debris flow ** Drainage basin (hydrology), a ...

in South America. Notable as an

obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym ''facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism that ...

air-breather, it is the sole member of its family native to the Americas. Relatively little is known about the South American lungfish, or ''scaly salamander-fish''. When immature it is spotted with gold on a black background. In the adult this fades to a brown or gray color. Its tooth-bearing

premaxillary The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...

and

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

ry bones are fused like other lungfish. South American lungfishes also share an autostylic jaw suspension (where the palatoquadrate is fused to the

cranium The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

) and powerful adductor jaw muscles with the extant lungfish (Dipnoi). Like the African lungfishes, this species has an elongate, almost eel-like body. It may reach a length of . The

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

s are thin and threadlike, while the pelvic fins are somewhat larger, and set far back. The fins are connected to the shoulder by a single bone, which is a marked difference from most fish, whose fins usually have at least four bones at their base; and a marked similarity with nearly all land-dwelling vertebrates. The gills are greatly reduced and essentially non-functional in the adults. Marbled lungfish 1

The marbled lungfish, ''Protopterus aethiopicus'', is found in Africa. The marbled lungfish is smooth, elongated, and cylindrical with deeply embedded

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...

. The tail is very long and tapers at the end. They are the largest of the African lungfish species as they can reach a length of up to 200 cm.Fishbase.org
/ref> The pectoral and pelvic fins are also very long and thin, almost spaghetti-like. The newly hatched young have branched external gills much like those of newts. After 2 to 3 months the young transform (called

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

) into the adult form, losing the

external gills External gills are the gills of an animal, most typically an amphibian, that are exposed to the environment, rather than set inside the pharynx and covered by gill slits, as they are in most fishes. Instead, the respiratory organs are set on a frill ...

for gill openings. These fish have a yellowish gray or pinkish toned ground color with dark slate-gray splotches, creating a marbling or leopard effect over the body and fins. The color pattern is darker along the top and lighter below. The marbled lungfish's

contains 133 billion

base pairs A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

, making it the largest known genome of any

. The only

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and ...

s known to have more base pairs are the

protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the exc ...

'' Polychaos dubium'' and the flowering plant ''

Paris japonica is a Japanese species of plants in the genus ''Paris'' in the family Melanthiaceae.Ohwi, J. (1984). Flora of Japan (in English): 1-1067. Smithsonian Institution, Washington, D.C.. It is native to sub-alpine regions of Japan. A slow growing per ...

'' at 670 billion and 150 billion, respectively.

The gilled lungfish, ''Protopterus amphibius'' is a species of lungfish found in

East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa: Due to the historical ...

. It generally reaches only long, making it the smallest

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

lungfish in the world. This lungfish is uniform blue, or slate grey in colour. It has small or inconspicuous black spots, and a pale grey belly. LepidosirenFord

The west African lungfish ''Protopterus annectens'' is a species of lungfish found in West Africa. It has a prominent

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...

and small

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

s. Its body is long and eel-like, some 9-15 times the length of the head. It has two pairs of long, filamentous fins. The

s have a basal fringe and are about three times the head length, while its

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two en ...

s are about twice the head length. In general, three external gills are inserted posterior to the

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In con ...

s and above the pectoral fins. It has

cycloid scale A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

s embedded in the skin. There are 40-50 scales between the operculum and the

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

and 36-40 around the body before the origin of the

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

. It has 34-37 pairs of

rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...

s. The dorsal side is olive or brown in color and the ventral side is lighter, with great blackish or brownish spots on the body and fins except on its belly. They reach a length of about 100 cm in the wild . Protopterus dolloi Boulenger2

The spotted lungfish, ''Protopterus dolloi'', is a species of lungfish found in Africa. Specifically, it is found in the Kouilou-Niari Basin of the

Republic of the Congo The Republic of the Congo (french: République du Congo, ln, Republíki ya Kongó), also known as Congo-Brazzaville, the Congo Republic or simply either Congo or the Congo, is a country located in the western coast of Central Africa to the w ...

and Ogowe River basin in

Gabon Gabon (; ; snq, Ngabu), officially the Gabonese Republic (french: République gabonaise), is a country on the west coast of Central Africa. Located on the equator, it is bordered by Equatorial Guinea to the northwest, Cameroon to the north ...

. It is also found in the lower and Middle Congo River Basins.Fishbase.org
/ref> ''Protopterus dolloi'' can

aestivate Aestivation ( la, aestas (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a ...

on land by surrounding itself in a layer of dried

mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is ...

. It can reach a length of up to 130 cm.

Taxonomy

The relationship of lungfishes to the rest of the

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...

is well understood: * Lungfishes are most closely related to ''

Powichthys ''Powichthys'' is a genus of prehistoric lobe-finned fish which lived during the Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ...

'', and then to the

Porolepiformes Porolepiformes is an order of prehistoric lobe-finned fish which lived during the Devonian period (about 416 to 359 million years ago). The group contains two families: Holoptychiidae and Porolepididae. Porolepiformes was established by the ...

. * Together, these taxa form the

Dipnomorpha Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

, the sister group to the Tetrapodomorpha. * Together, these form the

Rhipidistia Rhipidistia, also known as Dipnotetrapodomorpha, is a clade of lobe-finned fishes which includes the tetrapods and lungfishes. Rhipidistia formerly referred to a subgroup of Sarcopterygii consisting of the Porolepiformes and Osteolepiformes, a d ...

, the sister group to the coelacanths. Recent molecular genetic analyses strongly support a sister relationship of lungfishes and tetrapods (

), with coelacanths branching slightly earlier. The relationships among lungfishes are significantly more difficult to resolve. While Devonian lungfish had enough bone in the skull to determine relationships, post-Devonian lungfish are represented entirely by skull roofs and teeth, as the rest of the skull is cartilaginous. Additionally, many of the taxa already identified may not be

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

. Current phylogenetic studies support the following relationships of major lungfish taxa: Class Osteichthyes, subclass Sarcopterygii, order Dipnoi. In 2017, Anne Kemp, Lionel Calvin, and Guillaume Guinot found a different classification for more derived lungfish. In this new analysis, all extant lungfish belong in the suborder Ceratodontoidei, and despite their similar appearance there is no distinct clade containing only ''

Ceratodus ''Ceratodus'' (from el, κέρας , 'horn' and el, ὀδούς 'tooth') was a wide-ranging genus of extinct lungfish. Fossil evidence dates back to the Early Triassic. A wide range of fossil species from different time periods have been found ...

'', ''

Neoceratodus ''Neoceratodus'' is a genus of lungfish in the family Neoceratodontidae. The extant Australian lungfish (''Neoceratodus forsteri'') is the only surviving member of this genus, but it was formerly much more widespread, being distributed throughout ...

'', and their closest allies. New analyses of the relationships of the recently discovered ''Persephonichthys chthonica'' and modern lungfishes robustly places both taxa within dipterid-grade dipnoans rather than within a clade containing Late Devonian ‘phaneropleurids’ and common Late Paleozoic lungfishes such as ''

Sagenodus ''Sagenodus'' is an extinct genus of prehistoric lungfish. It is a lungfish from the Permo-Carboniferous period found in Europe and North America. See also * Sarcopterygii * List of sarcopterygians * List of prehistoric bony fish A ''list'' ...

''. Monophyly of post-Devonian lungfishes is not supported and the Carboniferous-Permian taxon ''Sagenodus'' is found to be incidental to the origins of modern lungfishes, suggesting widespread convergence in Late Paleozoic lungfishes.Pardo, Jason D et al. “An exceptionally preserved transitional lungfish from the lower permian of Nebraska, USA, and the origin of modern lungfishes.” PLOS ONE vol. 9,9 e108542. 29 Sep. 2014, doi:10.1371/journal.pone.0108542

Timeline of lungfish genera of the Devonian

ImageSize = width:1000px height:auto barincrement:15px PlotArea = left:10px bottom:50px top:10px right:10px Period = from:-416 till:-349.2 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:5 start:-416 ScaleMinor = unit:year increment:1 start:-416 TimeAxis = orientation:hor AlignBars = justify Colors = #legends id:CAR value:claret id:ANK value:rgb(0.4,0.3,0.196) id:HER value:teal id:HAD value:green id:OMN value:blue id:black value:black id:white value:white id:paleozoic value:rgb(0.6,0.75,0.55) id:cambrian value:rgb(0.49,0.63,0.33) id:ordovician value:rgb(0,0.57,0.44) id:silurian value:rgb(0.70,0.88,0.71) id:devonian value:rgb(0.8,0.55,0.22) id:earlydevonian value:rgb(0.90,0.71,0.43) id:middledevonian value:rgb(0.96,0.81,0.51) id:latedevonian value:rgb(0.96,0.89,0.71) id:carboniferous value:rgb(0.4,0.65,0.6) id:mississippian value:rgb(0.4,0.56,0.4) id:pennsylvanian value:rgb(0.8,0.77,0.53) id:permian value:rgb(0.94,0.25,0.24) id:mesozoic value:rgb(0.38,0.77,0.79) id:triassic value:rgb(0.51,0.17,0.57) id:jurassic value:rgb(0.2,0.7,0.79) id:cretaceous value:rgb(0.5,0.78,0.31) id:cenozoic value:rgb(0.95,0.98,0.11) id:paleogene value:rgb(0.99,0.6,0.32) id:neogene value:rgb(0.999999,0.9,0.1) id:quaternary value:rgb(0.98,0.98,0.50) BarData= bar:eratop bar:space bar:periodtop bar:space bar:NAM1 bar:NAM2 bar:NAM3 bar:NAM4 bar:NAM5 bar:NAM6 bar:NAM7 bar:NAM8 bar:NAM9 bar:NAM10 bar:NAM11 bar:NAM12 bar:NAM13 bar:NAM14 bar:NAM15 bar:NAM16 bar:NAM17 bar:space bar:period bar:space bar:era PlotData= align:center textcolor:black fontsize:M mark:(line,black) width:25 shift:(7,-4) bar:periodtop from: -416 till: -411.2 color:earlydevonian text: Lochkovian from: -411.2 till: -407 color:earlydevonian text:

Pragian The Pragian is one of three faunal stages in the Early Devonian Epoch. It lasted from 410.8 ± 2.8 million years ago to 407.6 ± 2.8 million years ago. It was preceded by the Lochkovian Stage and followed by the Emsian Stage. The most important La ...

from: -407 till: -397.5 color:earlydevonian text: Emsian from: -397.5 till: -391.8 color:middledevonian text: Eifelian from: -391.8 till: -385.3 color:middledevonian text: Givetian from: -385.3 till: -374.5 color:latedevonian text:

Frasnian The Frasnian is one of two faunal stages in the Late Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Givetian Stage and followed by the Famennian Stage. Major reef-building was under way during th ...

from: -374.5 till: -359.2 color:latedevonian text:

Famennian The Famennian is the latter of two faunal stages in the Late Devonian Epoch. The most recent estimate for its duration estimates that it lasted from around 371.1 million years ago to 359.3 million years ago. An earlier 2012 estimate, still used b ...

bar:eratop from: -416 till: -359.2 color:devonian text:

PlotData= align:left fontsize:M mark:(line,white) width:5 anchor:till align:left color:earlydevonian bar:NAM1 from:-416 till:-411.2 text: Diabolepis color:earlydevonian bar:NAM2 from:-416 till:-359.2 text: Devonesteus color:earlydevonian bar:NAM3 from:-416 till:-359.2 text:

Grossipterus ''Dipterus'' (from el, δίς , 'two' and el, πτερόν 'wing') is an extinct genus of lungfish from the middle Devonian period of Europe and North America. In most respects, ''Dipterus'', which was about long, closely resembled modern l ...

color:earlydevonian bar:NAM4 from:-416 till:-359.2 text:

Palaedaphus ''Palaedaphus'' is an extinct genus of prehistoric bony fish. See also * Prehistoric fish * List of prehistoric bony fish A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organizations ...

color:earlydevonian bar:NAM5 from:-411.2 till:-407 text:

Uranolophus ''Uranolophus'' is a genus of prehistoric lungfish which lived during the Late Devonian period. It is the type genus of the family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or ...

color:earlydevonian bar:NAM6 from:-411.2 till:-359.2 text:

Dipterus ''Dipterus'' (from el, δίς , 'two' and el, πτερόν 'wing') is an extinct genus of lungfish from the middle Devonian period of Europe and North America. In most respects, ''Dipterus'', which was about long, closely resembled modern ...

color:earlydevonian bar:NAM7 from:-407 till:-403.83 text:

Sponysedrion ''Sponysedrion'' is an extinct genus of prehistoric bony fish. See also * Prehistoric fish * List of prehistoric bony fish A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organizations ...

color:earlydevonian bar:NAM8 from:-407 till:-391.8 text:

Dipnorhynchus ''Dipnorhynchus'' is an extinct genus of lungfish from the middle Devonian period of Australia and Europe. ''Dipnorhynchus'' was a primitive lungfish, but still it had features that set it apart from other sarcopterygians. Its skull lacked the j ...

color:middledevonian bar:NAM9 from:-397.5 till:-385.3 text:

Melanognathus ''Melanognathus'' (Greek for "black jaw") is a genus of prehistoric lungfish which lived during the Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silur ...

color:middledevonian bar:NAM10 from:-397.5 till:-385.3 text:

Stomiahykus ''Stomiahykus'' is an extinct genus of prehistoric lobe-finned fish. See also * Prehistoric fish * List of prehistoric bony fish A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organiz ...

color:middledevonian bar:NAM11 from:-397.5 till:-359.2 text:

Rhinodipterus ''Rhinodipterus'' is an extinct genus of prehistoric dipnoan sarcopterygians or lobe-finned fish, that lived in the Devonian Period, between 416 and 359 million years ago. It is believed to have inhabited shallow, salt-water reefs, and is one of ...

color:middledevonian bar:NAM12 from:-391.8 till:-359.2 text:

Ganorhynchus ''Ganorhynchus'' is an extinct genus of prehistoric lungfish from the Devonian period. It is only found in Mansfield, Pennsylvania Mansfield is a Borough (Pennsylvania), borough located in east-central Tioga County, Pennsylvania, United States ...

color:middledevonian bar:NAM13 from:-387.5 till:-359.2 text: Conchodus color:latedevonian bar:NAM14 from:-385.3 till:-381.7 text: Chirodipterus color:latedevonian bar:NAM15 from:-385.3 till:-381.7 text:

Pillararhynchus ''Pillararhynchus'' is an extinct genus of prehistoric sarcopterygians or lobe-finned fish. See also * Sarcopterygii * List of sarcopterygians * List of prehistoric bony fish A ''list'' is any set of items in a row. List or lists may also re ...

color:latedevonian bar:NAM16 from:-385.3 till:-374.5 text:

Griphognathus ''Griphognathus'' (from el, γρίφος 'riddle') and el, γνάθος 'jaw') is an extinction, extinct genus of lungfish from the late Devonian period of Europe and Australia. ''Griphognathus'' was a specialized lungfish, about long, with ...

color:latedevonian bar:NAM17 from:-385.3 till:-374.5 text:

Holodipterus ''Holodipterus'' is an extinct genus of prehistoric sarcopterygian or lobe-finned fish.Campbell, KSW T., and R. E. Barwick. "Paleozoic lungfishes—a review."Journal of Morphology 190.S1 (1986): 93-131. Species * Holodipterus elderae * Holod ...

PlotData= align:center textcolor:black fontsize:M mark:(line,black) width:25 bar:period from: -416 till: -411.2 color:earlydevonian text: Lochkovian from: -411.2 till: -407 color:earlydevonian text:

from: -374.5 till: -359.2 color:latedevonian text:

bar:era from: -416 till: -359.2 color:devonian text:

References

External links

* * * * * {{Authority control Articles which contain graphical timelines Extant Early Devonian first appearances