58-561: Heterodontiformes is an order of sharks in the superorder Galeomorphii . It includes the bullhead sharks (genus Heterodontus ), and several extinct genera. The earliest known members of the group are from the Early Jurassic ( Toarcian ), around 175 million years ago. Several extinct genera are known from the Jurassic , with all except Paracestracion only known from isolated teeth. The teeth of heterodontiforms exhibit differerentation, with
116-430: A different reason. Unlike dolphins, these fish do not feel the bubbles, because they have bony fins without nerve endings. Nevertheless, they cannot swim faster because the cavitation bubbles create a vapor film around their fins that limits their speed. Lesions have been found on tuna that are consistent with cavitation damage. Scombrid fishes (tuna, mackerel and bonito) are particularly high-performance swimmers. Along
174-442: A homocercal tail. These come in a variety of shapes, and can appear: (D) - Diphycercal means the vertebrae extend to the tip of the tail and the tail is symmetrical and expanded (as in the bichir , lungfish , lamprey , coelacanths and † Tarrasiiformes ). Most Palaeozoic fishes had a diphycercal heterocercal tail. Finlets are small fins, generally behind the dorsal and anal fins (in bichirs , there are only finlets on
232-515: A liquid, which then promptly and violently collapse. It can cause significant damage and wear. Cavitation damage can occur to the tail fins of powerful swimming marine animals, such as dolphins and tuna. Cavitation is more likely to occur near the surface of the ocean, where the ambient water pressure is relatively low. Even if they have the power to swim faster, dolphins may have to restrict their speed because collapsing cavitation bubbles on their tail are too painful. Cavitation also slows tuna, but for
290-508: A modified fin to deliver sperm; thresher sharks use their caudal fin to whip and stun prey; reef stonefish have spines in their dorsal fins that inject venom as an anti-predator defense ; anglerfish use the first spine of their dorsal fin like a fishing rod to lure prey; and triggerfish avoid predators by squeezing into coral crevices and using spines in their fins to anchor themselves in place. Fins can either be paired or unpaired . The pectoral and pelvic fins are paired, whereas
348-439: A more disproportionate way than other fins on female fish." There are two prevailing hypotheses that have been historically debated as models for the evolution of paired fins in fish: the gill arch theory and the lateral fin-fold theory. The former, commonly referred to as the " Gegenbaur hypothesis ," was posited in 1870 and proposes that the "paired fins are derived from gill structures". This fell out of popularity in favor of
406-416: A neural network in the fin, indicating that it likely has a sensory function, but are still not sure exactly what the consequences of removing it are. A comparative study in 2013 indicates the adipose fin can develop in two different ways. One is the salmoniform-type way, where the adipose fin develops from the larval-fin fold at the same time and in the same direct manner as the other median fins. The other
464-705: A pancake, and will fit into fissures in rocks. Their pelvic and pectoral fins have evolved differently, so they act together with the flattened body to optimise manoeuvrability. Some fishes, such as puffer fish , filefish and trunkfish , rely on pectoral fins for swimming and hardly use tail fins at all. Male cartilaginous fishes (sharks and rays), as well as the males of some live-bearing ray finned fishes , have fins that have been modified to function as intromittent organs , reproductive appendages which allow internal fertilization . In ray finned fish, they are called gonopodia or andropodia , and in cartilaginous fish, they are called claspers . Gonopodia are found on
522-549: A prominent dorsal fin. Like scombroids and other billfish , they streamline themselves by retracting their dorsal fins into a groove in their body when they swim. The huge dorsal fin, or sail, of the sailfish is kept retracted most of the time. Sailfish raise them if they want to herd a school of small fish, and also after periods of high activity, presumably to cool down. The oriental flying gurnard has large pectoral fins which it normally holds against its body, and expands when threatened to scare predators. Despite its name, it
580-453: A subgroup of the order. Carpet sharks have two dorsal fins , without spines, and a small mouth that is forward of the eyes. Many have barbels and small gill slits , with the fifth slit overlapping the fourth. The upper lobe of the caudal fin tends to be mostly in line with the body, while the lower lobe is poorly developed. The order has around 43 species in seven families and 13 genera: Mackerel sharks are an order which includes some of
638-454: A thin stretch of scaleless skin ; in lobe-finned fish ( Sarcopterygii ) such as coelacanths and lungfish , fins are short rays based around a muscular central bud supported by jointed bones ; in cartilaginous fish ( Chondrichthyes ) and jawless fish ( Agnatha ), fins are fleshy " flippers " supported by a cartilaginous skeleton. Fins at different locations of the fish body serve different purposes, and are divided into two groups:
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#1732851342466696-413: Is a demersal fish , not a flying fish, and uses its pelvic fins to walk along the bottom of the ocean. Fins can have an adaptive significance as sexual ornaments. During courtship, the female cichlid , Pelvicachromis taeniatus , displays a large and visually arresting purple pelvic fin . "The researchers found that males clearly preferred females with a larger pelvic fin and that pelvic fins grew in
754-507: Is a stub . You can help Misplaced Pages by expanding it . Galeomorphii Galeomorphii is a superorder of sharks . They are sometimes called galea or galean sharks . There are about 300 living species in 23 families . Galean sharks are divided into four orders : the Heterodontiformes , Orectolobiformes , Lamniformes , and Carcharhiniformes . The extinct, enigmatic Synechodontiformes are presently placed by some authors in
812-614: Is one type of living lobe-finned fish. Both extant members of this group, the West Indian Ocean coelacanth ( Latimeria chalumnae ) and the Indonesian coelacanth ( Latimeria menadoensis ), are found in the genus Latimeria . Coelacanths are thought to have evolved roughly into their current form about 408 million years ago, during the early Devonian. Locomotion of the coelacanths is unique to their kind. To move around, coelacanths most commonly take advantage of up or downwellings of
870-436: Is prohibited in many countries. Foil shaped fins generate thrust when moved, the lift of the fin sets water or air in motion and pushes the fin in the opposite direction. Aquatic animals get significant thrust by moving fins back and forth in water. Often the tail fin is used, but some aquatic animals generate thrust from pectoral fins . Cavitation occurs when negative pressure causes bubbles (cavities) to form in
928-432: Is relatively conservative in lobe-finned fishes. However, there are a few examples from the fossil record that show aberrant morphologies , such as Allenypterus , Rebellatrix , Foreyia or the tetrapodomorphs . Ray-finned fishes form a class of bony fishes called Actinopterygii. Their fins contain spines or rays. A fin may contain only spiny rays, only soft rays, or a combination of both. If both are present,
986-402: Is something of a mystery. It is frequently clipped off to mark hatchery-raised fish, though data from 2005 showed that trout with their adipose fin removed have an 8% higher tailbeat frequency. Additional information released in 2011 has suggested that the fin may be vital for the detection of, and response to, stimuli such as touch, sound and changes in pressure. Canadian researchers identified
1044-487: Is the characiform-type way, where the adipose fin develops late after the larval-fin fold has diminished and the other median fins have developed. They claim the existence of the characiform-type of development suggests the adipose fin is not "just a larval fin fold remainder" and is inconsistent with the view that the adipose fin lacks function. Research published in 2014 indicates that the adipose fin has evolved repeatedly in separate lineages . (A) - Heterocercal means
1102-433: Is the heterocercal tail, which aids in locomotion. Most sharks have eight fins. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction. Unlike modern cartilaginous fish, members of stem chondrichthyan lineages (e.g. the † climatiids and the † diplacanthids ) possessed pectoral dermal plates as well as dermal spines associated with
1160-400: Is the largest class of vertebrates in existence today, making up more than 50% of species. In the distant past, lobe-finned fish were abundant; however, there are currently only 8 species. Bony fish have fin spines called lepidotrichia or "rays" (due to how the spines spread open). They typically have swim bladders , which allow the fish to alter the relative density of its body and thus
1218-587: Is thought that their rostral organ helps give the coelacanth electroperception, which aids in their movement around obstacles. Lungfish are also living lobe-finned fish. They occur in Africa ( Protopterus ), Australia ( Neoceratodus ), and South America ( Lepidosiren ). Lungfish evolved during the Devonian Period. Genetic studies and paleontological data confirm that lungfish are the closest living relatives of land vertebrates . Fin arrangement and body shape
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#17328513424661276-572: The Humane Society International , approximately 100 million sharks are killed each year for their fins, in an act known as shark finning . After the fins are cut off, the mutilated sharks are thrown back in the water and left to die. In some countries of Asia , shark fins are a culinary delicacy, such as shark fin soup . Currently, international concerns over the sustainability and welfare of sharks have impacted consumption and availability of shark fin soup worldwide. Shark finning
1334-477: The Middle Triassic † Saurichthys , the oldest known example of viviparity in a ray-finned fish. Claspers are found on the males of cartilaginous fishes . They are the posterior part of the pelvic fins that have also been modified to function as intromittent organs, and are used to channel semen into the female's cloaca during copulation. The act of mating in sharks usually includes raising one of
1392-417: The buoyancy , so it can sink or float without having to use the fins to swim up and down. However, swim bladders are absent in many fish, most notably in lungfishes , who have evolved their swim bladders into primitive lungs , which may have a shared evolutionary origin with those of their terrestrial relatives, the tetrapods . Bony fishes also have a pair of opercula that function to draw water across
1450-409: The extinct † Petalodontiformes (e.g. † Belantsea , † Janassa , † Menaspis ), which belong to Holocephali (ratfish and their fossil relatives), or in † Aquilolamna ( Selachimorpha ) and † Squatinactis (Squatinactiformes). Some cartilaginous fishes have an eel-like locomotion (e.g. Chlamydoselachus , † Thrinacoselache , † Phoebodus ) According to
1508-426: The gills , which help them breathe without needing to swim forward to force the water into the mouth across the gills. Lobe-finned fishes form a class of bony fishes called Sarcopterygii. They have fleshy, lobed , paired fins, which are joined to the body by a series of bones. The fins of lobe-finned fish differ from those of all other fish in that each is borne on a fleshy, lobe-like, scaly stalk extending from
1566-831: The midsagittal unpaired fins and the more laterally located paired fins . Unpaired fins are predominantly associated with generating linear acceleration via oscillating propulsion , as well as providing directional stability ; while paired fins are used for generating paddling acceleration , deceleration, and differential thrust or lift for turning , surfacing or diving and rolling . Fins can also be used for other locomotions other than swimming, for example, flying fish use pectoral fins for gliding flight above water surface, and frogfish and many amphibious fishes use pectoral and/or pelvic fins for crawling . Fins can also be used for other purposes: remoras and gobies have evolved sucker -like dorsal fins for attaching to surfaces and "hitchhiking"; male sharks and mosquitofish use
1624-471: The ventral portion. This is because the shark's vertebral column extends into that dorsal portion, providing a greater surface area for muscle attachment. This allows more efficient locomotion among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a homocercal caudal fin. Tiger sharks have a large upper lobe , which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in
1682-434: The ability to lock their spines outwards. Triggerfish also use spines to lock themselves in crevices to prevent them being pulled out. Lepidotrichia are usually composed of bone , but those of early osteichthyans - such as Cheirolepis - also had dentine and enamel . They are segmented and appear as a series of disks stacked one on top of another. They may have been derived from dermal scales. The genetic basis for
1740-514: The body. Pectoral and pelvic fins have articulations resembling those of tetrapod limbs. These fins evolved into legs of the first tetrapod land vertebrates ( amphibians ) in the Devonian Period . Sarcopterygians also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of most ray-finned fish (except some teleosts ). The caudal fin is either heterocercal (only fossil taxa ) or diphycercal. The coelacanth
1798-548: The claspers to allow water into a siphon through a specific orifice . The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position. The siphon then begins to contract expelling water and sperm. Other uses of fins include walking and perching on the sea floor, gliding over water, cooling of body temperature, stunning of prey, display (scaring of predators, courtship), defence (venomous fin spines, locking between corals), luring of prey, and attachment structures. The Indo-Pacific sailfish has
Heterodontiformes - Misplaced Pages Continue
1856-465: The current and drift. They use their paired fins to stabilize their movement through the water. While on the ocean floor their paired fins are not used for any kind of movement. Coelacanths can create thrust for quick starts by using their caudal fins. Due to the high number of fins they possess, coelacanths have high maneuverability and can orient their bodies in almost any direction in the water. They have been seen doing headstands and swimming belly up. It
1914-738: The dorsal surface and no dorsal fin). In some fish such as tuna or sauries , they are rayless, non-retractable, and found between the last dorsal and/or anal fin and the caudal fin. Bony fishes ( Actinopterygii and Sarcopterygii ) form a taxonomic group called Osteichthyes (or Euteleostomi , which includes also land vertebrates ); they have skeletons made of bone mostly, and can be contrasted with cartilaginous fishes (see below), which have skeletons made mainly of cartilage (except for their teeth , fin spines , and denticles ). Bony fishes are divided into ray-finned and lobe-finned fish . Most living fish are ray-finned, an extremely diverse and abundant group consisting of over 30,000 species . It
1972-525: The dorsal, anal and caudal fins are unpaired and situated along the midline of the body. For every type of fin, there are a number of fish species in which this particular fin has been lost during evolution (e.g. pelvic fins in † Bobasatrania , caudal fin in ocean sunfish ). In some clades , additional unpaired fins were acquired during evolution (e.g. additional dorsal fins, adipose fin). In some † Acanthodii ("spiny sharks"), one or more pairs of "intermediate" or "prepelvic" spines are present between
2030-442: The female. The male shortly inserts the organ into the sex opening of the female, with hook-like adaptations that allow the fish to grip onto the female to ensure impregnation. If a female remains stationary and her partner contacts her vent with his gonopodium, she is fertilized. The sperm is preserved in the female's oviduct. This allows females to fertilize themselves at any time without further assistance from males. In some species,
2088-400: The first dorsal fin spine was modified, forming a spine-brush complex. As with most fish, the tails of sharks provide thrust, making speed and acceleration dependent on tail shape. Caudal fin shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess a heterocercal caudal fin in which the dorsal portion is usually noticeably larger than
2146-501: The formation of a linked chain of vortex rings" and that "the dorsal and anal fin wakes are rapidly entrained by the caudal fin wake, approximately within the timeframe of a subsequent tail beat". Once motion has been established, the motion itself can be controlled with the use of other fins. The bodies of reef fishes are often shaped differently from open water fishes . Open water fishes are usually built for speed, streamlined like torpedoes to minimise friction as they move through
2204-553: The formation of the fin rays is thought to be genes coded for the production of certain proteins. It has been suggested that the evolution of the tetrapod limb from lobe-finned fishes is related to the loss of these proteins. Cartilaginous fishes form a class of fishes called Chondrichthyes. They have skeletons made of cartilage rather than bone . The class includes sharks , rays and chimaeras . Shark fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling
2262-494: The front teeth having well developed cusps to grasp prey, while the back teeth are flattened, and serve to crush hard shelled prey . They inhabit shallow littoral environments. Paracestracion exhibits notable anatomical differences from Heterodontus and is placed in its own family, Paracestracionidae within the order. The oldest known members of Heterodontus appeared during the Late Jurassic. This shark -related article
2320-460: The galeomorphs, but their taxonomic position still remains uncertain. The bullhead sharks are a small order of basal modern sharks ( Neoselachii ). All are relatively small, with the largest species being just 150 centimetres (59 in) in adult length. They are bottom feeders in tropical and subtropical waters. They appear in the fossil record in the Early Jurassic , well before any of
2378-510: The gonopodium may be half the total body length. Occasionally the fin is too long to be used, as in the "lyretail" breeds of Xiphophorus helleri . Hormone treated females may develop gonopodia. These are useless for breeding. Similar organs with similar characteristics are found in other fishes, for example the andropodium in the Hemirhamphodon or in the Goodeidae or the gonopodium in
Heterodontiformes - Misplaced Pages Continue
2436-410: The horny keratin in hair and feathers. Originally the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid and puboischiadic bars evolved. In rays , the pectoral fins have connected to the head and are very flexible. One of the primary characteristics present in most sharks
2494-402: The largest order of sharks, and include a number of common types such as the blue shark , catsharks, swellsharks and sandbar sharks . Members of the orders are characterized by the presence of a nictitating membrane over the eye, two dorsal fins , an anal fin , and five gill slits. The families in the order Carcharhiniformes are expected to be revised; recent DNA studies show that some of
2552-443: The lateral fin-fold theory, first suggested in 1877, which proposes that paired fins budded from longitudinal, lateral folds along the epidermis just behind the gills. There is weak support for both hypotheses in the fossil record and in embryology. However, recent insights from developmental patterning have prompted reconsideration of both theories in order to better elucidate the origins of paired fins. Carl Gegenbaur 's concept of
2610-493: The males of some species in the Anablepidae and Poeciliidae families. They are anal fins that have been modified to function as movable intromittent organs and are used to impregnate females with milt during mating. The third, fourth and fifth rays of the male's anal fin are formed into a tube-like structure in which the sperm of the fish is ejected. When ready for mating, the gonopodium becomes erect and points forward towards
2668-458: The margin at the rear of their bodies is a line of small rayless, non-retractable fins, known as finlets . There has been much speculation about the function of these finlets. Research done in 2000 and 2001 by Nauen and Lauder indicated that "the finlets have a hydrodynamic effect on local flow during steady swimming" and that "the most posterior finlet is oriented to redirect flow into the developing tail vortex, which may increase thrust produced by
2726-501: The most familiar species of sharks, such as the great white shark , as well as more unusual representatives, such as the goblin shark and the megamouth shark . Members of the order are distinguished by possessing two dorsal fins , an anal fin , five gill slits , eyes without nictitating membranes , and a mouth extending behind the eyes. Mackerel sharks may also refer specifically to the family Lamnidae . The order includes seven families and sixteen living species: Ground sharks are
2784-420: The other galean sharks. However, they have never been common, and it is likely their origin lies even further back. There are nine living species in a single genus, Heterodontus and a single family. Carpet sharks are another small order of sharks, so called because many members have ornate patterns reminiscent of carpets. Sometimes the term "carpet shark" is used interchangeably with wobbegong , which are
2842-690: The paired fins. The oldest species demonstrating these features is the † acanthodian † Fanjingshania renovata from the lower Silurian ( Aeronian ) of China. Fanjingshania possess compound pectoral plates composed of dermal scales fused to a bony plate and fin spines formed entirely of bone. Fin spines associated with the dorsal fins are rare among extant cartilaginous fishes, but are present, for instance, in Heterodontus or Squalus . Dorsal fin spines are typically developed in many fossil groups, such as in † Hybodontiformes , † Ctenacanthiformes or † Xenacanthida . In † Stethacanthus ,
2900-403: The pectoral and pelvic fins, but these are not associated with fins. The pelvic fin assists the fish in going up or down through the water, turning sharply, and stopping quickly. The dorsal fins are located on the back. A fish can have up to three dorsal fins. The dorsal fins serve to protect the fish against rolling, and assist it in sudden turns and stops. The function of the adipose fin
2958-402: The spiny rays are always anterior . Spines are generally stiff and sharp. Rays are generally soft, flexible, segmented, and may be branched. This segmentation of rays is the main difference that separates them from spines; spines may be flexible in certain species, but they will never be segmented. Spines have a variety of uses. In catfish , they are used as a form of defense; many catfish have
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#17328513424663016-552: The tail of swimming mackerel". Fish use multiple fins, so it is possible that a given fin can have a hydrodynamic interaction with another fin. In particular, the fins immediately upstream of the caudal (tail) fin may be proximate fins that can directly affect the flow dynamics at the caudal fin. In 2011, researchers using volumetric imaging techniques were able to generate "the first instantaneous three-dimensional views of wake structures as they are produced by freely swimming fishes". They found that "continuous tail beats resulted in
3074-450: The tip of the tail and the tail is symmetrical but not expanded (as in the first fishes and the cyclostomes , and a more primitive precursor in lancelets ) (C) - Homocercal where the fin usually appears superficially symmetric but in fact the vertebrae extend for a very short distance into the upper lobe of the fin. Homocercal caudal fins can, however, also appear asymmetric (e.g. blue flying fish ). Most modern fishes ( teleosts ) have
3132-643: The traditional groups are not monophyletic . The order includes eight families and over 270 species: Anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim . Apart from the tail or caudal fin , fish fins have no direct connection with the back bone and are supported only by muscles . Fish fins are distinctive anatomical features with varying structures among different clades : in ray-finned fish ( Actinopterygii ), fins are mainly composed of bony spines or rays covered by
3190-419: The vertebrae extend into the upper lobe of the tail, often making it longer than the lower lobe (as in sharks , † Placodermi , most stem Actinopterygii , and sturgeons and paddlefish ). However, the external shape of heterocercal tail fins can also appear symmetric (e.g. † Birgeria , † Bobasatrania ). Heterocercal is the opposite of hypocercal (B) - Protocercal means the vertebrae extend to
3248-511: The water easily when hunting to support its varied diet, whereas the porbeagle shark , which hunts schooling fish such as mackerel and herring , has a large lower lobe to help it keep pace with its fast-swimming prey. Other tail adaptations help sharks catch prey more directly, such as the thresher shark 's usage of its powerful, elongated upper lobe to stun fish and squid. On the other hand, rays rely on their enlarged pectoral fins for propulsion. Similarly enlarged pectoral fins can be found in
3306-697: The water. Reef fish operate in the relatively confined spaces and complex underwater landscapes of coral reefs . For this manoeuvrability is more important than straight line speed, so coral reef fish have developed bodies which optimize their ability to dart and change direction. They outwit predators by dodging into fissures in the reef or playing hide and seek around coral heads. The pectoral and pelvic fins of many reef fish, such as butterflyfish , damselfish and angelfish , have evolved so they can act as brakes and allow complex manoeuvres. Many reef fish, such as butterflyfish , damselfish and angelfish , have evolved bodies which are deep and laterally compressed like
3364-522: The “Archipterygium” was introduced in 1876. It was described as a gill ray, or "joined cartilaginous stem," that extended from the gill arch. Additional rays arose from along the arch and from the central gill ray. Gegenbaur suggested a model of transformative homology – that all vertebrate paired fins and limbs were transformations of the Archipterygium. Based on this theory, paired appendages such as pectoral and pelvic fins would have differentiated from
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