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54-485: 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 . They are characterized by high-ridged toothplates that form cutting blades and a reduction in cranial bones. Previously, based on morphological evidence, it

108-528: A common lineal origin, it is now viewed as analogous, convergent , or from a different lineal origin. Pikaia appears to have a proto-notochord, and notochords are present in several basal chordates such as Haikouella , Haikouichthys , and Myllokunmingia , all from the Cambrian . The Ordovician oceans included many diverse species of Agnatha and early Gnathostomata which possessed notochords, either with attached bony elements or without, most notably

162-410: A critical role in signaling the development of motor neurons. The secretion of SHH by the notochord establishes the ventral pole of the dorsal-ventral axis in the developing embryo. The notochord is the defining feature ( synapomorphy ) of chordates , and was present throughout life in many of the earliest chordates. Although the stomochord of hemichordates was once thought to be homologous or from

216-468: A fan-shaped occlusion surface. These odontodes then wear to form a uniform crushing surface. In several groups, including the modern lepidosireniformes , 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 among the vertebrates. Modern lungfish all have an elongate body with fleshy, paired pectoral and pelvic fins and

270-464: A homologous structure, the axochord, that was present in annelid-like ancestors of the chordates). Deciding between these two scenarios (or possibly another yet to be proposed) should be facilitated by much more thorough studies of gene regulatory networks in a wide spectrum of animals. In most vertebrates, the notochord develops into secondary structures. In other chordates , the notochord is retained as an essential anatomical structure. The evolution of

324-449: A layer of dried mucus . It can reach a length of up to 130 cm. The relationship of lungfishes to the rest of the bony fish is well understood: Recent molecular genetic analyses strongly support a sister relationship of lungfishes and tetrapods ( Rhipidistia ), with coelacanths branching slightly earlier. The relationships among lungfishes are significantly more difficult to resolve. While Devonian lungfish had enough bone in

378-472: A pale grey belly. The west African lungfish , Protopterus annectens , is a species of lungfish found in West Africa. It has a prominent snout and small eyes . 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 pectoral fins have a basal fringe and are about three times the head length, while its pelvic fins are about twice

432-420: A second notochord near the dorsal neural tube, 180 degrees opposite of the normal notochord location, one can induce the formation of motor neurons in the dorsal tube. Motor neuron formation generally occurs in the ventral neural tube, while the dorsal tube generally forms sensory cells . The notochord secretes a protein called sonic hedgehog (SHH), a key morphogen regulating organogenesis and having

486-409: A significant reduction in the marginal bones and a cartilaginous braincase. The bones of the skull roof in primitive lungfish are covered in a mineralized tissue called cosmine , but in post- Devonian 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

540-441: A single unpaired caudal fin replacing the dorsal , caudal and anal fins of most fishes. Lungfish have a highly specialized respiratory system . 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 bladders , these bladders are usually simple sacs, devoid of complex internal structure. In contrast,

594-441: 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 allow it to slow its metabolism to as little as one sixtieth of the normal metabolic rate, and protein waste is converted from ammonia to less-toxic urea (normally, lungfish excrete nitrogenous waste as ammonia directly into

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648-469: 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. They have the lowest aquatic respiration of all extant lungfish species, and their gills are greatly reduced and essentially non-functional in the adults. The marbled lungfish , Protopterus aethiopicus , is found in Africa. The marbled lungfish

702-432: Is a transient structure ventral to the notochord, and is primarily responsible for correct development of the dorsal aorta. Notochord flexion , when the notochord bends to form a part of the developing caudal fin, is a hallmark of an early growth stage of some fish. By the age of 4, all notochord residue is replaced by a population of chondrocyte -like cells of unclear origin. Persistence of notochordal cells within

756-410: Is derived from the embryonic mesoderm and consists of an inner core of vacuolated cells filled with glycoproteins , covered by two helical collagen - elastin sheaths. It lies along the rostral - caudal axis of the body (i.e. longitudinally or " head to tail "), dorsal to the gut tube and ventral to the dorsal nerve cord . Some chordates, such as tunicates , develop notochord during

810-419: Is found ventral to the neural tube . Notogenesis is the development of the notochord by epiblasts that form the floor of the amnion cavity. The progenitor notochord is derived from cells migrating from the primitive node and pit. The notochord forms during gastrulation and soon after induces the formation of the neural plate ( neurulation ), synchronizing the development of the neural tube . On

864-449: Is found in the nucleus pulposus of the intervertebral discs. Isolated notochordal remnants may escape their lineage-specific destination in the nucleus pulposus and instead attach to the outer surfaces of the vertebral bodies , from which notochordal cells largely regress. During development of amphibians and fish, the notochord induces development of the hypochord through secretion of vascular endothelial growth factor . The hypochord

918-501: Is smooth, elongated, and cylindrical with deeply embedded scales . 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. 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 ) into

972-497: 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. Lungfish are omnivorous , feeding on fish, insects , crustaceans , worms , mollusks , amphibians and plant matter. They have an intestinal spiral valve rather than

1026-506: The Australian lungfish can breathe through its gills without needing air from its lung. In other species, the gills are too atrophied to allow for adequate gas exchange. When a lungfish is obtaining oxygen 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,

1080-1000: The Gzhelian through the Roadian . In Africa, gnathorhizids are found in Olenekian of Madagascar and possibly South Africa. Lungfish teeth attributed to gnathorhizids have been reported from the Lopingian to the Olenekian in Poland and Western Russia. It is likely, then, that gnathorhizids had a Pangean distribution throughout the late Paleozoic and early Mesozoic . Gnathorhizids are found primarily in paleosols representing ephemeral wetlands . Additionally, gnathorhizids, unlike most groups of fossil lungfish, are often found in association with regular burrow structures, suggesting this group of lungfish may have estivated during

1134-863: The class Dipnoi . Lungfish are best known for retaining ancestral characteristics within the Osteichthyes , 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 tetrapods (which includes living amphibians, reptiles, birds and mammals). The mouths of lungfish typically bear tooth plates, which are used to crush hard shelled organisms . Today there are only six known species of lungfish, living in Africa , South America , and Australia , though they were formerly globally distributed. The fossil record of

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1188-423: The conodonts , placoderms , and ostracoderms . Even after the evolution of the vertebral column in chondrichthyes and osteichthyes , these taxa remained common and are well represented in the fossils record. Several species (see list below) have reverted to the primitive state, retaining the notochord into adulthood, though the reasons for this are not well understood. Scenarios for the evolutionary origin of

1242-453: The cranium ) 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 125 centimetres (4 ft 1 in). The pectoral fins 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

1296-545: The gut tube and ventral to the neural tube . The notochord is composed primarily of a glycoproteins core that is encased in a sheath of collagen fibers. This is wound into two opposing helices . The glycoproteins are stored in vacuolated, turgid cells, which are covered with caveolae on their cell surface. The angle between these fibers determines whether increased pressure in the core will result in shortening and thickening versus lengthening and thinning. Alternating contraction of muscle fibers attached to each side of

1350-403: The larval stage but lose it through subsequent stages into adulthood. The notochord is important for signaling the dorso-ventral patterning of cells coming from the mesodermal progenitors. This helps form the precursors needed for certain organs and the embryo to develop. In summary, the notochord plays essential roles in embryonic development. The notochord provides a directional reference to

1404-412: The mesoderm , which grows medially and surrounds it. From the mesoderm surrounding the neural tube and notochord, the skull , vertebral column, and the membranes of the brain and medulla spinalis are developed. Because it originates from the primitive node and is ultimately positioned with the mesodermal space, it is considered to be derived from mesoderm. A postembryonic vestige of the notochord

1458-501: The protist Polychaos dubium and the flowering plant Paris japonica at 670 billion and 150 billion, respectively. The gilled lungfish , Protopterus amphibius is a species of lungfish found in East Africa . It generally reaches only 44 centimetres (17 inches) long, making it the smallest extant lungfish in the world. This lungfish is uniform blue, or slate grey in colour. It has small or inconspicuous black spots, and

1512-410: The ventral aspect of the neural groove, an axial thickening of the endoderm takes place. (In bipedal chordates, e.g. humans, this surface is properly referred to as the anterior surface). This thickening appears as a furrow (the chordal furrow) the margins of which anastomose (come into contact), and so convert it into a solid rod of polygonal-shaped cells (the notochord) which is then separated from

1566-529: 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 and maxillary bones are fused like other lungfish. South American lungfishes also share an autostylic jaw suspension (where the palatoquadrate is fused to

1620-582: The Late Carboniferous and the Jurassic . Lungfish remained present in the northern Laurasian landmasses into the Cretaceous period. The Queensland lungfish , Neoceratodus forsteri , is endemic to Australia. Fossil records of this group date back 380 million years, around the time when the higher vertebrate classes were beginning to evolve. Fossils of lungfish belonging to

1674-434: The adult animal, and the notochord is not vacuolated. In all vertebrates other than the hagfish , the notochord is present only during early embryonic development and is later replaced by the bony and/or cartilaginous vertebral column , with its original structure being integrated into the intervertebral discs as the nucleus pulposus . The notochord is a long, rod-like midline structure that develops dorsal to

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1728-459: The adult form, losing the external gills 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 genome contains 133 billion base pairs , making it the largest known genome of any vertebrate . The only organisms known to have more base pairs are

1782-677: The ancestor of the extant coelacanths diverging a little earlier from a sarcopterygian progenitor. Youngolepis and Diabolepis , dating to 419–417 million years ago, during Early Devonian ( Lochkovian ), are the currently oldest known lungfish, and show that the lungfishes had adapted to a diet including hard-shelled prey ( durophagy ) very early in their evolution. The earliest lungfish were marine. Almost all post- Carboniferous lungfish inhabit or inhabited freshwater environments. There were likely at least two transitions amongst lungfish from marine to freshwater habitats. The last common ancestor of all living lungfish likely lived sometime between

1836-668: The body and fins except on its belly. They reach a length of about 100 cm in the wild. 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 and Ogowe River basin in Gabon . It is also found in the lower and Middle Congo River Basins . Protopterus dolloi can aestivate on land by surrounding itself in

1890-528: The dry season, much like modern African and South American lungfish. Unlike most fossil lungfish, but again, like modern South American and African lungfish, gnathorhizids have bladelike toothplates. This suggests gnathorhizids were active predators unlike most lungfish, which feed primarily on benthic invertebrates . [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Lungfish Fossil taxa, see text Lungfish are freshwater vertebrates belonging to

1944-399: The endoderm. In vertebrates, it extends throughout the entire length of the future vertebral column, and reaches as far as the anterior end of the midbrain , where it ends in a hook-like extremity in the region of the future dorsum sellae of the sphenoid bone . Initially, it exists between the neural tube and the endoderm of the yolk-sac; soon, the notochord becomes separated from them by

1998-749: The genus Neoceratodus have been uncovered in northern New South Wales , indicating that the Queensland lungfish has existed in Australia for at least 100 million years, making it a living fossil 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 in Africa and one in South America, are very different morphologically to N. forsteri . The Queensland lungfish can live for several days out of

2052-726: The group extends into the Early Devonian , over 410 million years ago. The earliest known members of the group were marine, while almost all post- Carboniferous representatives inhabit freshwater environments. Modern Latin from the Greek δίπνοος (dipnoos) with two breathing structures, from δι- twice and πνοή breathing, breath. All lungfish demonstrate an uninterrupted cartilaginous notochord and an extensively developed palatal dentition. Basal (" primitive ") lungfish groups may retain marginal teeth and an ossified braincase, but derived lungfish groups, including all modern species, show

2106-449: The head length. In general, three external gills are inserted posterior to the gill slits and above the pectoral fins. It has cycloid scales embedded in the skin. There are 40–50 scales between the operculum and the anus and 36–40 around the body before the origin of the dorsal fin . It has 34–37 pairs of ribs . The dorsal side is olive or brown in color and the ventral side is lighter, with great blackish or brownish spots on

2160-493: 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 to the lungs of tetrapods. As in tetrapods and bichirs , the lungs extend from the ventral surface of the esophagus and gut. Of extant lungfish, only

2214-406: The notochord result in a side-to-side motion resembling stern sculling , which allows tail swimming and undulation . The stiffened notochord prevents movement through telescoping motion such as that of an earthworm . The notochord plays a key role in signaling and coordinating development. Embryos of modern vertebrates form transient notochord structures during gastrulation . The notochord

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2268-423: The notochord were comprehensively reviewed by Annona, Holland, and D'Aniello (2015). They point out that, although many of these ideas have not been well supported by advances in molecular phylogenetics and developmental genetics, two of them have actually been revived under the stimulus of modern molecular approaches (the first proposes that the notochord evolved de novo in chordates, and the second derives it from

2322-400: The notochord within the phylum Chordata is considered in detail by Holland and Somorjai (2020). Vertebrates now have spines so they do not need a notochord. The following organisms retain a post-embryonic notochord: The notochord of the lancelet (amphioxus) protrudes beyond the anterior end of the neural tube. This projection serves a second purpose in allowing the animal to burrow within

2376-510: The oldest lungfish, and probably the oldest aquarium fish in the world is " Methuselah ", an Australian lungfish 4 feet (1.2 m) long and weighing around 40 pounds (18 kg). Methuselah is believed to be female, unlike its namesake , and is estimated to be over 90 years old. About 420 million years ago, during the Devonian , the last common ancestor of both lungfish and the tetrapods split into two separate evolutionary lineages, with

2430-436: 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. When breathing air,

2484-474: The skull roof show no homology to the skull roof bones of ray-finned fishes or tetrapods . During the breeding season, the South American lungfish 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 , lungfishes have evolved internal nostrils similar to

2538-753: 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 . Phylogeny after Kemp, Cavin & Guinot, 2017 † Diabolepis † Westollrhynchus † Ichnomylax † Dipnorhynchus † Speonesydrion † Uranolophus † Stomiahykus † Iowadipterus † Jessenia † Melanognathus † Tarachomylax † Dipterus † Adololopas † Chirodipterus australis † Gogodipterus † Pillararhynchus † Sorbitorhynchus † Chirodipterus liangchengi † Chirodipterus wildungensis † Sinodipterus Notochord The notochord

2592-407: 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

2646-432: The surrounding tissue as a midline structure during the embryonic development , acts as a precursor for vertebrae and a primitive axial endoskeleton , and can allow for facilitated tail motion when swimming. In cephalochordates ( lancelets ), the notochord persists throughout life as the main structural support of the body. In tunicates , the notochord is present only in the larval stage, becoming completely absent in

2700-472: The tetrapods' choana , and a brain with certain similarities to Lissamphibian 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 group. " Odontodes " on the palate and lower jaws develop in a series of rows to form

2754-456: The vertebra may cause a pathologic condition: persistent notochordal canal . If the notochord and the nasopharynx do not separate properly during embryonic development, a depression (Tornwaldt bursa) or Tornwaldt cyst may form. The cells are the likely precursors to a rare cancer called chordoma . Research into the notochord has played a key role in understanding the development of the central nervous system . By transplanting and expressing

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2808-458: The water if it is kept moist, but will not survive total water depletion, unlike its African counterparts. 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 the sole member of its family native to

2862-680: The water). Burrowing is seen in at least one group of fossil lungfish, the Gnathorhizidae . Lungfish can be extremely long-lived. A Queensland lungfish called "Granddad" at the Shedd Aquarium in Chicago was part of the permanent live collection from 1933 to 2017 after a previous residence at the Sydney Aquarium ; at 109 years old, it was euthanized following a decline in health consistent with old age. As of 2022,

2916-738: Was assumed that Gnathorhizidae was the sister group to the extant families Lepidosirenidae and Protopteridae , which still live in South America and Africa . However, phylogenetic evidence indicates that Gnathorhizidae is a basal group of freshwater lungfish with no close extant relatives, and African and South American lungfish are most closely related to Australian lungfish in Neoceratodontidae . Gnathorhizids are found in North America, Eastern Europe, Australia, and Africa. Gnathorhizids from North America range from

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