Carp are various species of oily freshwater fish from the family Cyprinidae, a large group of fish native to Europe and Asia. The cypriniformes are traditionally grouped with the Characiformes and Gymnotiformes to create the superorder Ostariophysi, since these groups share some common features; these features include being found predominantly in fresh water and possessing Weberian ossicles, an anatomical structure derived from the first five anterior-most vertebrae, their corresponding ribs and neural crests. The third anterior-most pair of ribs is in contact with the extension of the labyrinth and the posterior with the swim bladder; the function is poorly understood, but this structure is presumed to take part in the transmission of vibrations from the swim bladder to the labyrinth and in the perception of sound, which would explain why the Ostariophysi have such a great capacity for hearing. Most cypriniformes have scales and teeth on the inferior pharyngeal bones which may be modified in relation to the diet.
Tribolodon is the only cyprinid genus. Several species return to fresh water to spawn. All of the other cypriniformes have a wide geographical range; some consider all cyprinid fishes carp, the family Cyprinidae itself is known as the carp family. In colloquial use, carp refers only to several larger cyprinid species such as Cyprinus carpio, Carassius carassius, Ctenopharyngodon idella, Hypophthalmichthys molitrix, Hypophthalmichthys nobilis. Carp have long been an important food fish to humans. Several species such as the various goldfish breeds and the domesticated common carp variety known as koi have been popular ornamental fishes; as a result, carp have been introduced to various locations, though with mixed results. Several species of carp are listed as invasive species by the U. S. Department of Agriculture, worldwide, large sums of money are spent on carp control. At least some species of carp are able to survive for months with no oxygen by metabolizing glycogen to form lactic acid, converted into ethanol and carbon dioxide.
The ethanol diffuses into the surrounding water through the gills. In 1653 Izaak Walton wrote in The Compleat Angler, "The Carp is the queen of rivers. Carp are variable in terms of angling value. In Europe when not fished for food, they are eagerly sought by anglers, being considered prized coarse fish that are difficult to hook; the UK has a thriving carp angling market. It is the fastest growing angling market in the UK, has spawned a number of specialised carp angling publications such as Carpology, Advanced carp fishing and Total Carp, informative carp angling web sites, such as Carpfishing UK. In the United States, carp are classified as a rough fish, as well as damaging to naturalized exotic species, but with sporting qualities. Carp have long suffered from a poor reputation in the United States as undesirable for angling or for the table since they are an invasive species out-competing more desirable local game fish. Nonetheless, many states' departments of natural resources are beginning to view the carp as an angling fish instead of a maligned pest.
Groups such as Wild Carp Companies, American Carp Society, the Carp Anglers Group promote the sport and work with fisheries departments to organize events to introduce and expose others to the unique opportunity the carp offers freshwater anglers. Various species of carp have been domesticated and reared as food fish across Europe and Asia for thousands of years; these various species appear to have been domesticated independently, as the various domesticated carp species are native to different parts of Eurasia. Aquaculture has been pursued in China for at least 2,400 years. A tract by Fan Li in the fifth century BC details many of the ways carp were raised in ponds; the common carp, Cyprinus carpio, is from Central Europe. Several carp species were domesticated in East Asia. Carp that are from South Asia, for example catla and mrigal, are known as Indian carp, their hardiness and adaptability have allowed domesticated species to be propagated all around the world. Although the carp was an important aquatic food item, as more fish species have become available for the table, the importance of carp culture in Western Europe has become less important.
Demand has declined due to the appearance of more desirable table fish such as trout and salmon through intensive farming, environmental constraints. However, fish production in ponds is still a major form of aquaculture in Central and Eastern Europe, including the Russian Federation, where most of the production comes from low or intermediate-intensity ponds. In Asia, the farming of carp continues to surpass the total amount of farmed fish volume of intensively sea-farmed species, such as salmon and tuna. Selective breeding programs for the common carp include improvement in growth and resistance to disease. Experiments carried out in the USSR used crossings of broodstocks to increase genetic diversity, selected the species for traits such as growth rate, exterior traits and viability, and/or adaptation to environmental conditions such as variations in temperature. Selected carp for fast growth and tolerance to cold, the Ropsha carp; the results showed a 30 to 77.4% improvement of cold tolerance, but did not provide any data for growth
Reptiles are tetrapod animals in the class Reptilia, comprising today's turtles, snakes, lizards and their extinct relatives. The study of these traditional reptile orders combined with that of modern amphibians, is called herpetology; because some reptiles are more related to birds than they are to other reptiles, the traditional groups of "reptiles" listed above do not together constitute a monophyletic grouping or clade. For this reason, many modern scientists prefer to consider the birds part of Reptilia as well, thereby making Reptilia a monophyletic class, including all living Diapsids; the earliest known proto-reptiles originated around 312 million years ago during the Carboniferous period, having evolved from advanced reptiliomorph tetrapods that became adapted to life on dry land. Some early examples include Casineria. In addition to the living reptiles, there are many diverse groups that are now extinct, in some cases due to mass extinction events. In particular, the Cretaceous–Paleogene extinction event wiped out the pterosaurs, plesiosaurs and sauropods, as well as many species of theropods, including troodontids, dromaeosaurids and abelisaurids, along with many Crocodyliformes, squamates.
Modern non-avian reptiles inhabit all the continents except Antarctica, although some birds are found on the periphery of Antarctica. Several living subgroups are recognized: Testudines, 350 species. Reptiles are tetrapod vertebrates, creatures that either have four limbs or, like snakes, are descended from four-limbed ancestors. Unlike amphibians, reptiles do not have an aquatic larval stage. Most reptiles are oviparous, although several species of squamates are viviparous, as were some extinct aquatic clades – the fetus develops within the mother, contained in a placenta rather than an eggshell; as amniotes, reptile eggs are surrounded by membranes for protection and transport, which adapt them to reproduction on dry land. Many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings. Extant reptiles range in size from a tiny gecko, Sphaerodactylus ariasae, which can grow up to 17 mm to the saltwater crocodile, Crocodylus porosus, which can reach 6 m in length and weigh over 1,000 kg.
In the 13th century the category of reptile was recognized in Europe as consisting of a miscellany of egg-laying creatures, including "snakes, various fantastic monsters, assorted amphibians, worms", as recorded by Vincent of Beauvais in his Mirror of Nature. In the 18th century, the reptiles were, from the outset of classification, grouped with the amphibians. Linnaeus, working from species-poor Sweden, where the common adder and grass snake are found hunting in water, included all reptiles and amphibians in class "III – Amphibia" in his Systema Naturæ; the terms "reptile" and "amphibian" were interchangeable, "reptile" being preferred by the French. Josephus Nicolaus Laurenti was the first to formally use the term "Reptilia" for an expanded selection of reptiles and amphibians similar to that of Linnaeus. Today, the two groups are still treated under the same heading as herptiles, it was not until the beginning of the 19th century that it became clear that reptiles and amphibians are, in fact, quite different animals, Pierre André Latreille erected the class Batracia for the latter, dividing the tetrapods into the four familiar classes of reptiles, amphibians and mammals.
The British anatomist Thomas Henry Huxley made Latreille's definition popular and, together with Richard Owen, expanded Reptilia to include the various fossil "antediluvian monsters", including dinosaurs and the mammal-like Dicynodon he helped describe. This was not the only possible classification scheme: In the Hunterian lectures delivered at the Royal College of Surgeons in 1863, Huxley grouped the vertebrates into mammals and ichthyoids, he subsequently proposed the names of Ichthyopsida for the latter two groups. In 1866, Haeckel demonstrated that vertebrates could be divided based on their reproductive strategies, that reptiles and mammals were united by the amniotic egg; the terms "Sauropsida" and "Theropsida" were used again in 1916 by E. S. Goodrich to distinguish between lizards and their relatives on the one hand and mammals and their extinct relatives on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, other features, such as the structure of the forebrain.
According to Goodrich, both lineages evolved from an earlier stem group, Protosauria in which he included some animals today considered reptile-like amphibians, as well as early reptiles. In 1956, D. M. S. Watson observed that the first two groups diverged early in reptilian history, so he divided Goodrich's Protosauria between them, he reinterpreted Sauropsida and Theropsida to exclude birds and mammals, respectively. Thus his Sauropsida included Procolophonia, Millerosauria, Squamata, Rhynchocephalia
A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals carnivores use teeth for hunting or for defensive purposes; the roots of teeth are covered by gums. Teeth hardness; the cellular tissues that become teeth originate from the embryonic germ layer, the ectoderm. The general structure of teeth is similar across the vertebrates, although there is considerable variation in their form and position; the teeth of mammals have deep roots, this pattern is found in some fish, in crocodilians. In most teleost fish, the teeth are attached to the outer surface of the bone, while in lizards they are attached to the inner surface of the jaw by one side. In cartilaginous fish, such as sharks, the teeth are attached by tough ligaments to the hoops of cartilage that form the jaw; some animals develop only one set of teeth. Sharks, for example, grow a new set of teeth. Rodent incisors grow and wear away continually through gnawing, which helps maintain constant length.
The industry of the beaver is due in part to this qualification. Many rodents such as voles and guinea pigs, but not mice, as well as leporidae like rabbits, have continuously growing molars in addition to incisors. Teeth are not always attached to the jaw. In many reptiles and fish, teeth are attached to the palate or to the floor of the mouth, forming additional rows inside those on the jaws proper; some teleosts have teeth in the pharynx. While not true teeth in the usual sense, the dermal denticles of sharks are identical in structure and are to have the same evolutionary origin. Indeed, teeth appear to have first evolved in sharks, are not found in the more primitive jawless fish – while lampreys do have tooth-like structures on the tongue, these are in fact, composed of keratin, not of dentine or enamel, bear no relationship to true teeth. Though "modern" teeth-like structures with dentine and enamel have been found in late conodonts, they are now supposed to have evolved independently of vertebrates' teeth.
Living amphibians have small teeth, or none at all, since they feed only on soft foods. In reptiles, teeth are simple and conical in shape, although there is some variation between species, most notably the venom-injecting fangs of snakes; the pattern of incisors, canines and molars is found only in mammals, to varying extents, in their evolutionary ancestors. The numbers of these types of teeth vary between species; the genes governing tooth development in mammals are homologous to those involved in the development of fish scales. Study of a tooth plate of a fossil of the extinct fish Romundina stellina showed that the teeth and scales were made of the same tissues found in mammal teeth, lending support to the theory that teeth evolved as a modification of scales. Teeth are among the most distinctive features of mammal species. Paleontologists use teeth to determine their relationships; the shape of the animal's teeth are related to its diet. For example, plant matter is hard to digest, so herbivores have many molars for chewing and grinding.
Carnivores, on the other hand, have canine teeth to tear meat. Mammals, in general, are diphyodont. In humans, the first set starts to appear at about six months of age, although some babies are born with one or more visible teeth, known as neonatal teeth. Normal tooth eruption at about six months can be painful. Kangaroos and manatees are unusual among mammals because they are polyphyodonts. In Aardvarks, teeth lack enamel and have many pulp tubules, hence the name of the order Tubulidentata. In dogs, the teeth are less than humans to form dental cavities because of the high pH of dog saliva, which prevents enamel from demineralizing. Sometimes called cuspids, these teeth are shaped like points and are used for tearing and grasping food Like human teeth, whale teeth have polyp-like protrusions located on the root surface of the tooth; these polyps are made of cementum in both species, but in human teeth, the protrusions are located on the outside of the root, while in whales the nodule is located on the inside of the pulp chamber.
While the roots of human teeth are made of cementum on the outer surface, whales have cementum on the entire surface of the tooth with a small layer of enamel at the tip. This small enamel layer is only seen in older whales where the cementum has been worn away to show the underlying enamel; the toothed whale is a suborder of the cetaceans characterized by having teeth. The teeth differ among the species, they may be numerous, with some dolphins bearing over 100 teeth in their jaws. On the other hand, the narwhals have a giant unicorn-like tusk, a tooth containing millions of sensory pathways and used for sensing during feeding and mating, it is the most neurologically complex tooth known. Beaked whales are toothless, with only bizarre teeth found in males; these teeth may be used for feeding but for demonstrating aggression and showmanship. In humans there are 20 primary teeth, 28 to 32 of what's known as permanent teeth, in addition to other four being third molars or wisdom teeth, each of which may or may not g
Pangolins or scaly anteaters are mammals of the order Pholidota. The one extant family, has three genera: Manis, which comprises four species living in Asia; these species range in size from 30 to 100 cm. A number of extinct pangolin species are known. Pangolins have protective keratin scales covering their skin, they live depending on the species. Pangolins are nocturnal, their diet consists of ants and termites, which they capture using their long tongues, they tend to be solitary animals, meeting only to mate and produce a litter of one to three offspring, which are raised for about two years. Pangolins are threatened by poaching and heavy deforestation of their natural habitats, are the most trafficked mammals in the world. Of the eight species of pangolin, four are listed as vulnerable, two are listed as endangered, two are listed as critically endangered on the International Union for Conservation of Nature Red List of Threatened Species; the name pangolin comes from the Malay word pengguling, meaning "one who rolls up".
However, the modern name in Standard Malay is tenggiling. The etymologies of the three generic names Manis and Smutsia are sometimes misunderstood. Carl Linnaeus invented the Neo-Latin generic name Manis as a feminine singular form of the Latin masculine plural Manes, the Ancient Roman name for a type of spirit, after the animal's strange appearance. Constantine Rafinesque formed the Neo-Latin generic name Phataginus from the French term phatagin, adopted by Count Buffon after the reported local name phatagin or phatagen used in the East Indies; the British naturalist John Edward Gray named Smutsia for the South African naturalist Johannes Smuts, the first South African to do a treatise on mammals in 1832. The physical appearance of a pangolin is marked by large hardened overlapping plate-like scales, which are soft on newborn pangolins, but harden as the animal matures, they are made of keratin, the same material from which human fingernails and tetrapod claws are made, are structurally and compositionally different from the scales of reptiles.
The pangolin's scaled body is comparable in appearance to a pine cone. It can curl up into a ball when threatened, with its overlapping scales acting as armor, while it protects its face by tucking it under its tail; the scales are sharp. Pangolins can emit a noxious-smelling chemical from glands near the anus, similar to the spray of a skunk, they have short legs, with sharp claws which they use for burrowing into ant and termite mounds, climbing. The tongues of pangolins are long and – like those of the giant anteater and the tube-lipped nectar bat – the root of the tongue is not attached to the hyoid bone, but is in the thorax between the sternum and the trachea. Large pangolins can extend their tongues as much as 40 cm, with a diameter of only 0.5 cm. Most pangolins are nocturnal animals; the long-tailed pangolin is active by day, while other species of pangolins spend most of the daytime sleeping, curled up into a ball. They are considered to be secretive creatures. Arboreal pangolins live in hollow trees, whereas the ground-dwelling species dig tunnels underground, to a depth of 3.5 m.
Some pangolins walk with their front claws bent under the foot pad, although they use the entire foot pad on their rear limbs. Furthermore, some may walk a few steps bipedally. Pangolins are good swimmers. Pangolins are insectivorous. Most of their diet consists of various species of ants and termites and may be supplemented by other insects larvae, they are somewhat particular and tend to consume only one or two species of insects when many species are available to them. A pangolin can consume 140 to 200 g of insects per day. Pangolins are an important regulator of termite populations in their natural habitats. Pangolins have a poor sense of vision, so they rely on smell and hearing. Pangolins lack teeth, therefore they have evolved other physical characteristics to help them eat ants and termites, their skeletal structure is sturdy and they have strong front legs that are useful for tearing into termite mounds. They use their powerful front claws to dig into trees and vegetation to find prey proceed to use their long tongues to probe inside the insect tunnels and to retrieve their prey.
The structure of their tongue and stomach is key to aiding pangolins in obtaining and digesting insects. Their saliva is sticky, causing ants and termites to stick to their long tongues when they are hunting through insect tunnels. Without teeth, pangolins lack the ability to chew; this part of their stomach is called the gizzard, it is covered in keratinous spines. These spines further aid in digestion of the pangolin's prey; some species, such as the tree pangolin, use their strong, prehensile tails to hang from tree branches and
Salmon is the common name for several species of ray-finned fish in the family Salmonidae. Other fish in the same family include trout, char and whitefish. Salmon are native to tributaries of the North Pacific Ocean. Many species of salmon have been introduced into non-native environments such as the Great Lakes of North America and Patagonia in South America. Salmon are intensively farmed in many parts of the world. Salmon are anadromous: they hatch in fresh water, migrate to the ocean return to fresh water to reproduce. However, populations of several species are restricted to fresh water through their lives. Folklore has it. Tracking studies have shown this to be true. A portion of a returning salmon run may spawn in different freshwater systems. Homing behavior has been shown to depend on olfactory memory. Salmon date back to the Neogene; the term "salmon" comes from the Latin salmo, which in turn might have originated from salire, meaning "to leap". The nine commercially important species of salmon occur in two genera.
The genus Salmo contains the Atlantic salmon, found in the north Atlantic, as well as many species named trout. The genus Oncorhynchus contains eight species which occur only in the North Pacific; as a group, these are known as Pacific salmon. Chinook salmon have been introduced in New Patagonia. Coho, freshwater sockeye, Atlantic salmon have been established in Patagonia, as well. † Both the Salmo and Oncorhynchus genera contain a number of species referred to as trout. Within Salmo, additional minor taxa have been called salmon in English, i.e. the Adriatic salmon and Black Sea salmon. The steelhead anadromous form of the rainbow trout migrates to sea, but it is not termed "salmon". A number of other species have common names which refer to them as being salmon. Of those listed below, the Danube salmon or huchen is a large freshwater salmonid related to the salmon above, but others are marine fishes of the unrelated Perciformes order: Eosalmo driftwoodensis, the oldest known salmon in the fossil record, helps scientists figure how the different species of salmon diverged from a common ancestor.
The British Columbia salmon fossil provides evidence that the divergence between Pacific and Atlantic salmon had not yet occurred 40 million years ago. Both the fossil record and analysis of mitochondrial DNA suggest the divergence occurred by 10 to 20 million years ago; this independent evidence from DNA analysis and the fossil record rejects the glacial theory of salmon divergence. Atlantic salmon reproduce in northern rivers on both coasts of the Atlantic Ocean. Landlocked salmon live in a number of lakes in eastern North America and in Northern Europe, for instance in lakes Sebago, Ladoga, Saimaa, Vänern, Winnipesaukee, they are not a different species from the Atlantic salmon, but have independently evolved a non-migratory life cycle, which they maintain when they could access the ocean. Chinook salmon are known in the United States as king salmon or blackmouth salmon, as spring salmon in British Columbia. Chinook are the largest of all Pacific salmon exceeding 14 kg; the name tyee is used in British Columbia to refer to Chinook over 30 pounds, in the Columbia River watershed large Chinook were once referred to as June hogs.
Chinook salmon are known to range as far north as the Mackenzie River and Kugluktuk in the central Canadian arctic, as far south as the Central California coast. Chum salmon are known as dog, keta, or calico salmon in some parts of the US; this species has the widest geographic range of the Pacific species: south to the Sacramento River in California in the eastern Pacific and the island of Kyūshū in the Sea of Japan in the western Pacific. Coho salmon are known in the US as silver salmon; this species is found throughout the coastal waters of Alaska and British Columbia and as far south as Central California. It is now known to occur, albeit infrequently, in the Mackenzie River. Masu salmon or cherry salmon are found only in the western Pacific Ocean in Japan and Russia. A land-locked subspecies known as the Taiwanese salmon or Formosan salmon is found in central Taiwan's Chi Chia Wan Stream. Pink salmon, known as humpies in southeast and southwest Alaska, are found from northern California and Korea, throughout the northern Pacific, from the Mackenzie River in Canada to the Lena River in Siberia in shorter coastal streams.
It is the smallest of the Pacific species, with an average weight of 1.6 to 1.8 kg. Sockeye salmon are known in the US as red salmon; this lake-rearing species is found south as far as the Klamath River in California in the eastern Pacific and northern Hokkaidō island in Japan in the western Pacific and as far north as Bathurst Inlet in the Canadian Arctic in the east and the Anadyr River in Siberia in the west. Although most adult Pacific salmon feed on small fish and squid, sockeye feed on plankton they filter through gill rakers. Kokanee salmon are the land-locked form of sockeye salmon. Danube salmon, or huchen, are the largest permanent freshwater salmonid species. Salmon eggs are laid in freshwater streams at high latitudes; the eggs hatch into alevin or sac fry
The skin of most fishes is covered with protective scales, which can provide effective camouflage through the use of reflection and colouration, as well as possible hydrodynamic advantages. Scales vary enormously in size, shape and extent, ranging from strong and rigid armour plates in fishes such as shrimpfishes and boxfishes, to microscopic or absent in fishes such as eels and anglerfishes; the morphology of a scale can be used to identify the species of fish. Cartilaginous fishes are covered with placoid scales. Most bony fishes are covered with the cycloid scales of salmon and carp, or the ctenoid scales of perch, or the ganoid scales of sturgeons and gars; some species are covered instead by scutes, others have no outer covering on the skin. Fish scales are part of the fish's integumentary system, are produced from the mesoderm layer of the dermis, which distinguishes them from reptile scales; the same genes involved in tooth and hair development in mammals are involved in scale development.
The placoid scales of cartilaginous fishes are called dermal denticles and are structurally homologous with vertebrate teeth. It has been suggested that the scales of bony fishes are similar in structure to teeth, but they originate from different tissue. Most fish are covered in a protective layer of mucus; the bony scales of thelodonts, the most abundant form of fossil fish, are well understood. The scales were formed and shed throughout the organisms' lifetimes, separated after their death. Bone, a tissue, both resistant to mechanical damage and prone to fossilization preserves internal detail, which allows the histology and growth of the scales to be studied in detail; the scales comprise a non-growing "crown" composed of dentine, with a sometimes-ornamented enameloid upper surface and an aspidine base. Its growing base is made of cell-free bone, which sometimes developed anchorage structures to fix it in the side of the fish. Beyond that, there appear to be five types of bone-growth, which may represent five natural groupings within the thelodonts—or a spectrum ranging between the end members meta- dentine and mesodentine tissues.
Each of the five scale morphs appears to resemble the scales of more derived groupings of fish, suggesting that thelodont groups may have been stem groups to succeeding clades of fish. However, using scale morphology alone to distinguish species has some pitfalls. Within each organism, scale shape varies hugely according to body area, with intermediate forms appearing between different areas—and to make matters worse, scale morphology may not be constant within one area. To confuse things further, scale morphologies are not unique to taxa, may be indistinguishable on the same area of two different species; the morphology and histology of thelodonts provides the main tool for quantifying their diversity and distinguishing between species, although using such convergent traits is prone to errors. Nonetheless, a framework comprising three groups has been proposed based upon scale morphology and histology. Comparisons to modern shark species have shown that thelodont scales were functionally similar to those of modern cartilaginous fish, has allowed an extensive comparison between ecological niches.
Cosmoid scales are found in several ancient lobe-finned fishes, including some of the earliest lungfishes, were derived from a fusion of placoid scales. They are composed of a layer of dense, lamellar bone called isopedine, above, a layer of spongy bone supplied with blood vessels; the bone layers are covered by a complex dentine layer called cosmine and a superficial outer coating of vitrodentine. Cosmoid scales increase in size through the growth of the lamellar bone layer. Ganoid scales are found in the sturgeons, gars and bichirs, they are derived from cosmoid scales and have serrated edges. They are covered with a layer of hard enamel-like dentine in the place of cosmine, a layer of inorganic bone salt called ganoine in place of vitrodentine. Most are diamond-shaped and connected by peg-and-socket joints, they are thick and have a minimal amount of overlap as compared to other scales. In this way, ganoid scales are excellent protection against predation. In sturgeons, the scales are enlarged into armour plates along the sides and back, while in the bowfin the scales are reduced in thickness to resemble cycloid scales.
Native Americans and people of the Caribbean used the tough ganoid scales of the alligator gar for arrow heads, as shielding to cover plows. In current times jewellery is made from these scales. Elasmoid scales are thin, imbricated scales composed of a layer of dense, lamellar bone called isopedine, above, a layer of tubercles composed of bone, as in Eusthenopteron; the layer of dentine, present in the first sarcopterygians is reduced, as in the extant coelacanth, or absent, as in extant lungfish and in the Devonian Eusthenopteron. Elasmoid scales have appeared several times over the course of fish evolution, they are present in some lobe-finned fishes: coelacanths, all extant and some extinct lungfishes, some tetrapodomorphs like Eusthenopteron and teleosts, whose cycloid and ctenoid scales represent the least mineralized elasmoid scales. Placoid scales are found in the cartilaginous fishes: sharks and chimaeras, they are called dermal denticles. Placoid scales are structurally homologous with vertebrate teeth, having a central pulp cavity supplied with blood vessels, surrounded by a conical layer of dentine, all of which sits on top of a r
The Sarcopterygii or lobe-finned fish —sometimes considered synonymous with Crossopterygii —constitute a clade of the bony fish, though a strict cladistic view includes the terrestrial vertebrates. The living sarcopterygians include six species of lungfish. Early lobe-finned fishes are bony fish with fleshy, paired fins, which are joined to the body by a single bone; the fins of lobe-finned fishes differ from those of all other fish in that each is borne on a fleshy, scaly stalk extending from the body. The scales of sarcopterygians are true scaloids, consisting of lamellar bone surrounded by layers of vascular bone, dentine-like cosmine, external keratin; the morphology of tetrapodomorphs, fish that are similar-looking to tetrapods, give indications of the transition from water to terrestrial life. Pectoral and pelvic fins have articulations resembling those of tetrapod limbs; these fins evolved into the legs of the first tetrapod land vertebrates, amphibians. They possess two dorsal fins with separate bases, as opposed to the single dorsal fin of actinopterygians.
The braincase of sarcopterygians primitively has a hinge line, but this is lost in tetrapods and lungfish. Many early sarcopterygians have a symmetrical tail. All sarcopterygians possess teeth covered with true enamel. Most species of lobe-finned fishes are extinct; the largest known lobe-finned fish was Rhizodus hibberti from the Carboniferous period of Scotland which may have exceeded 7 meters in length. Among the two groups of extant species, the coelacanths and the lungfishes, the largest species is the West Indian Ocean coelacanth, reaching 2 m in length and weighing up 110 kg; the largest lungfish is the African lungfish which can weigh up to 50 kg. Taxonomists who subscribe to the cladistic approach include the grouping Tetrapoda within this group, which in turn consists of all species of four-limbed vertebrates; the fin-limbs of lobe-finned fishes such as the coelacanths show a strong similarity to the expected ancestral form of tetrapod limbs. The lobe-finned fishes followed two different lines of development and are accordingly separated into two subclasses, the Rhipidistia and the Actinistia.
The classification below follows Benton 2004, uses a synthesis of rank-based Linnaean taxonomy and reflects evolutionary relationships. Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii in order to reflect the direct descent of tetrapods from lobe-finned fish, despite the former being assigned a higher taxonomic rank. Subclass Sarcopterygii †Order Onychodontida Order Actinistia Infraclass Dipnomorpha †Order Porolepiformes Subclass Dipnoi Order Ceratodontiformes Order Lepidosireniformes Infraclass Tetrapodomorpha †Order Rhizodontida Superorder Osteolepidida †Order Osteolepiformes †Family Tristichopteridae †Order Panderichthyida Superclass Tetrapoda The cladogram presented below is based on studies compiled by Philippe Janvier and others for the Tree of Life Web Project, Mikko's Phylogeny Archive and Swartz 2012. Sarcopterygii incertae sedis †Guiyu oneiros Zhu et al. 2009 †Diabolepis speratus †Langdenia campylognatha Janvier & Phuong, 1999 †Ligulalepis Schultze, 1968 †Meemannia eos Zhu, Yu, Zhao & Jia, 2006 †Psarolepis romeri Yu 1998 sensu Zhu, Yu, Zhao & Jia, 2006 †Megamastax ambylodus Choo, Zhao, Jia, & Zhu, 2014 †Sparalepis tingi Choo,Zhu,Qu,Yu,Jia & Zhaoh, 2017 Paraphyletic Osteolepida incertae sedis: †Bogdanovia orientalis Obrucheva 1955 †Canningius groenlandicus Säve-Söderbergh, 1937 †Chrysolepis †Geiserolepis †Latvius †L. grewingki †L. porosus Jarvik, 1948 †L. obrutus Vorobyeva, 1977 †Lohsania utahensis Vaughn, 1962 †Megadonichthys kurikae Vorobyeva, 1962 †Platyethmoidia antarctica Young, Long & Ritchie, 1992 †Shirolepis ananjevi Vorobeva, 1977 †Sterropterygion brandei Thomson, 1972 †Thaumatolepis edelsteini Obruchev, 1941 †Thysanolepis micans Vorobyeva, 1977 †Vorobjevaia dolonodon Young, Long & Ritchie, 1992 Paraphyletic Elpistostegalia/Panderichthyida incertae sedis †Parapanderichthys stolbovi Vorobyeva, 1992 †Howittichthys warrenae Long & Holland, 2008 †Livoniana multidentata Ahlberg, Luksevic & Mark-Kurik, 2000 Stegocephalia incertae sedis †Antlerpeton clarkii Thomson, Shubin & Poole, 1998 †Austrobrachyops jenseni Colbert & Cosgriff, 1974 †Broilisaurus raniceps Kuhn, 1938 †Densignathus rowei Daeschler, 2000 †Doragnathus woodi Smithson, 1980 †Jakubsonia livnensis Lebedev, 2004 †Limnerpeton dubium Fritsch, 1901 †Limnosceloides Romer, 1952 †L. dunkardensis Romer, 1952 †L. brahycoles Langston, 1966 †Occidens portlocki Clack & Ahlberg, 2004 †Ossinodus puerorum emend Warren & Turner, 2004 †Romeriscus periallus Baird & Carroll, 1968 †Sigournea multidentata Bolt & Lombard, 2006 †Sinostega pani Zhu et al. 2002 †Ymeria denticulata Clack et al. 2012 Lobe-finned fishes and their relatives the ray-finned fishes comprise the superclass of bony fishes characterized by their bony skeleton rather than cartilage.
There are otherwise vast differences in fin and circulatory structures between the Sarcopterygii and the Actinopterygii, such as the presence of cosmoid layers in the scales of sarcopterygians. The earliest fossils of sarcopterygians, found in the uppermost Silurian resembled the