Hammerheads
| Hammerheads | ||||||||||||
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Great hammerhead shark ( Sphyrna mokarran ) |
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| Systematics | ||||||||||||
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| Sphyrnidae | ||||||||||||
| Gill , 1872 |
The hammerheads (Sphyrnidae) are a family of sharks , which are particularly characterized by the strong widening of their head to a so-called cephalofoil ; in some species this leads to the formation of the eponymous “hammer”. The family comprises two genera with a total of eight species , which differ mainly in their size, shape and width of the head. The largest species is the great hammerhead shark ( Sphyrna mokarran ) with a maximum length of 5.50 to 6.10 meters, while the corona hammerhead shark ( Sphyrna corona ) as the smallest species only reaches a maximum total length of less than one meter.
Hammerheads live mainly in tropical and subtropical coastal areas around the world. They are usually solitary, although some species can form groups of several hundred to several thousand individuals. As hunters, they prey on a variety of invertebrates as well as bone and cartilaginous fish. Larger individuals also prey on other sharks, including smaller members of their own species ( cannibalism ). Above all, prey animals living on the ground such as various rays are detected by the sensory organs located on the cephalofoil. All hammerheads are viviparous and form a placenta for the care of the young by the mother. The large species are classified as potentially dangerous, but shark accidents with hammerhead sharks are very rarely documented. Some species are hunted commercially, primarily because of their fins; individual species are classified as “endangered” to “critically endangered” by the International Union for Conservation of Nature (IUCN) due to the strong fishing pressure .
features
Hammerhead sharks have a streamlined body. The longest known representative is the great hammerhead shark ( Sphyrna mokarran ) with a maximum total length of 5.50 to 6.10 meters, while the corona hammerhead shark as the smallest species only reaches a maximum of 92 centimeters. The coloring of the species is usually brownish to gray with a white belly, a mark is only present in the shovel-nosed hammerhead shark in the form of irregular spots and in some species in the form of dark fin tips or edges. A special feature is the golden yellow to orange coloration of the small-eyed hammerhead , which can probably be traced back to its main food. In young animals it consists of shrimps that are very rich in carotenoids and in sexually mature sharks from fish and fish roe , which also contain these pigments.
The strong widening of the head directly in front of the gills (prebranchial) is particularly noticeable; it is also strongly flattened in some species. The resulting head shape is the most important distinguishing feature of the species due to its typical characteristics of a broadened to hammer-shaped head ( cephalofoil ). The head broadening of the species of the genus Sphyrna is between 17 and 33 percent of the total length, in the winged hammerhead shark ( Eusphyra blochii ) even 40 to 50 percent. The eyes are located on the side at the end of the cephalofoil, are round or almost round and have an inner nictitating membrane . The nostrils have short, lobed nasal valves; the distance between the nostrils at the leading edge of the cephalofoil is 7 to 14 times the nostril diameter; an exception is the wingtip hammerhead with its very enlarged nostrils, where the distance is only 1.1 to 1.3 times the nostril diameter. The mouth lies below the cephalofoil and is usually parabolic in shape. The labial furrows are indistinct or completely absent. The teeth in the upper and lower jaws of hammerheads differ very little from one another: They are comparatively small to moderately large, are more or less blade-shaped and have only a narrow central point with no secondary points; basal ridges and furrows can be formed or absent. In the upper jaw there are 25 to 37 teeth on one half of the jaw and 24 to 37 teeth in the lower jaw, behind which further rows of teeth are laid out.
Hammerhead sharks have five gill slits , the spray hole is reduced in all species. The first dorsal fin begins approximately in the middle between the pectoral and pectoral fins, in some species also closer to the end of the pectoral fins; the middle of the dorsal fin is always in front of the attachment of the pelvic fins. It is moderately to very large and sickle-shaped, the second dorsal fin and the anal fin are significantly smaller. There are pits in front of the approach of the caudal fin. It is asymmetrical with a very large upper and a significantly smaller, but also strongly developed lower lobe. The upper caudal lobe is always significantly larger than the first dorsal fin.
In addition to these external features, there are some features of the head skeleton and spine that are typical of hammerhead sharks. The neurocranium has no primary supraorbital ridges; instead, extensions of the pre- and postorbital bones fuse into secondary supraorbital ridges that are unique among sharks. The centers of the vertebral bodies form strong, wedge-shaped and cross-vertebral calcifications.
Function of widening the head
The function and thus the evolutionary origin and development of the hammerhead cephalofoil has not been conclusively clarified. It is assumed, among other things, that the widening of the head mainly serves to improve the maneuverability of the shark, and it also increases its field of perception. The former also led to the name "Cephalofoil" ("head rudder surface"), which was derived from the English name "Airfoil" for wing profile in aircraft construction. In terms of functionality, the cephalofoil corresponds to the canard wing that is used in aircraft construction and enables height control through additional wings on the aircraft nose. The main aim is to improve maneuverability and lift in very tight turns. Due to the additional buoyancy aid, the pectoral fins can be made relatively small compared to other sharks.
The eyes and the greatly enlarged nasal pits of these sharks are at the end of the broadening, so that the field that these sensory organs perceive is greatly expanded. This also applies to the Lorenzini ampoules on the front of the cephalofoil , which in hammerhead sharks not only perceive electrical impulses from potential prey fish, but also the earth's magnetic field and would thus serve as an orientation aid during the migrations that are typical for some hammerhead sharks.
In 2002, a comparative mathematical modeling of the perception of electromagnetic fields by the Lorenzini ampoules confirmed the optimized detection of prey from a hammer-headed shark compared to a round-headed shark. While in other sharks, such as the blue shark ( Prionace glauca ), the perception channels of the Lorenzini ampoules are essentially circularly aligned with a center in the middle of the head, in a hammer-headed shark they are centered on three centers. It was found that this significantly improves both the intensity of perception and the directional allocation of the electromagnetic fields caused by the potential prey. McComb et al. were able to prove experimentally in 2009 that the particularly strong widening of the head of the wingtip hammerhead and the bowhead hammerhead also significantly improves visual perception. According to their investigations, sharks with a wide cephalofoil have a significantly larger field of vision as well as an also greatly enlarged overlap area in which two-eyed and thus three-dimensional ( binocular vision ) is possible.
Other hypotheses assume that the broad head is used to fix prey, especially stingrays and other rays, on the sea floor, as was observed above all in the great hammerhead shark. This was derived, among other things, from an observation of a great hammerhead shark that captured an American stingray ( Dasyatis americana ) in the Bahamas . The shark first hit the ray with an attack from above on the ocean floor and then held it there with its broad head while it turned and bit vigorously on both sides of the enlarged pectoral fins. The stingray, unable to move, was lifted off with its mouth and dismantled with rapid head movements of the shark. In another sighting, a great hammerhead shark was observed attacking a spotted eagle ray ( Aetobatus narinari ) in the open water by biting a large piece from one of the two pectoral fins and then pressing it with its head on the ground, where it also hit the ray took it head first in its mouth. Based on these observations, it is assumed that hammerhead sharks when hunting rays first try to make them unable to escape with the first bite and then use the widened head to bring the prey under control and hold it on the ground.
distribution
Hammerhead sharks can be found worldwide mainly in tropical and subtropical coastal areas of the oceans. Some species occur in very large areas, for example the great hammerhead and the bow-fronted hammerhead shark are found worldwide in warmer climates, while the smooth hammerhead shark can also be found in temperate areas and even migrates to more Polish and cooler areas in summer. The smaller species are all restricted to smaller areas of distribution; the wingtip hammerhead shark is found in the Red Sea and on the Asian coasts of the Indian Ocean as far as northern Australia, the white-fin hammerhead shark is only found on the Atlantic coasts of Europe and north-west Africa and the shovel-nosed hammerhead shark is only found on the tropical coasts of North and South America. The smallest area of distribution has the corona hammerhead, which is distributed on the Pacific coast of America from the Gulf of California to Peru .
Hammerhead sharks live mainly in the coastal areas as well as the continental shelf and in the area of archipelagos and are only very rarely found in regions with greater water depths. The deepest sea depths are reached by the bow-forehead hammerhead, which can also occur at depths of more than 270 meters, while among the other great hammerheads, the great hammerhead shark seldom falls below 80 meters and the smooth hammerhead shark, as a pronounced surface dweller, usually not below 20 meters sea depth lives. The smaller species as well as the young of the large species live almost exclusively in the shallow water area, with the small-eyed hammerhead shark in particular having adapted to cloudy and muddy bays and estuaries due to the regression of its eyes .
Way of life
Hammerhead sharks are usually solitary, but can also form small to very large groups ( schools ). The smooth and bow-fronted hammerhead in particular regularly form groups of several hundred to several thousand individuals.
The adult individuals of the great hammerhead shark species generally have no predators, with the exception of the great killer whale ( Orcinus orca ). The smaller species as well as the juveniles of the larger species are mainly preyed on by other shark species such as bull sharks ( Carcharhinus leucas ). Occasionally schools of pilot fish ( Naucrates ductor ) accompany larger sharks, including the great hammerhead shark. Jacks have been seen rubbing their flanks on the skin of great and smooth hammerhead sharks, likely to rub off skin parasites on themselves. The main parasites of hammerhead sharks are Copepoda as skin parasites and some roundworms as intestinal parasites.
nutrition
The food of the larger and free-swimming hammerheads consists primarily of bony fish such as sardines , herrings and mackerel , but barracudas and other larger fish are also accepted as prey by large individuals. The sharks also feed on invertebrates , especially cephalopods such as cuttlefish and squid, and crustaceans. In addition, they also hunt small sharks such as sharp -nosed sharks , nurse sharks or blacktip reef sharks as well as rays .
The great and smooth hammerhead in particular prey on rays , especially stingrays . The stingrays' poison stings are regularly found stabbed in the mouth of hammerhead sharks and do not seem to bother them. A great hammerhead shark caught off the coast of Florida had 96 spines stuck in and around its mouth. These sharks hunt mainly at night or during twilight, swinging their head in large arcs over the sea floor and using their Lorenzini ampoules located on the cephalofoil to detect electrical signals of possible prey. At the same time, the head acts as a wing , which allows the sharks to quickly turn around and catch a prey they have just discovered.
Especially the smaller species feed to a large extent on invertebrates, mainly crustaceans . The shovel-nose hammerhead in particular has specialized in hard-shelled crustaceans such as crabs , shrimps and barnacles as well as mussels ( durophagy ): The rear teeth, which have a high point in the other species, are significantly flattened (molar-shaped) and enable the shark to to break the hard shells. In this species, the jaw muscles and thus the functioning of the jaw are adapted to the hard food. In its youth, the small-eye hammerhead feeds primarily on shrimp, which contain a high proportion of carotenoids and thus cause the sharks to turn yellow; later he hunts larger invertebrates and fish and also feeds on fish roe.
Reproduction
All hammerheads are viviparous (ovoviviparous), whereby the unborn young sharks are nourished in the uterus via a yolk sac placenta . After it has been consumed by the young sharks, the yolk sac is transformed into a placenta, which is analogous to that of mammals and ensures nutrition via the maternal bloodstream in the course of further development. The number of young sharks depends on the type and size. It ranges from probably only 2 juveniles in the corona hammerhead to over 30 juveniles in the large, smooth and bow-forehead hammerhead. For the birth, bow-fronted hammerhead sharks usually go to shallower sea regions, where the young sharks also spend the first years of their lives. In the winged hammerhead shark, which is characterized by an extremely wide head even as a young animal, the two head wings lie on the body before birth and only unfold after birth.
On December 14, 2001, a female shovel-nosed hammerhead shark gave birth to a young without fertilization by a male at the Henry Doorly Zoo in Omaha , Nebraska, USA. A DNA test found the genetic makeup of a male partner was missing, confirming parthenogenesis in sharks for the first time . In the meantime, asexual reproduction has also been reported by the white-spotted bamboo shark ( Chiloscyllium punctatum ), the white-tip reef shark ( Triaenodon obesus ) and the small black -tip shark ( Carcharhinus limbatus ).
Evolution and systematics
Fossil record
As with other sharks, fossils of hammerheads are mainly in the form of teeth, whereby all finds were assigned to the genus Sphyrna , which still exists today . The oldest fossil finds of hammerhead sharks come from the Palaeocene of North America ( Charles County , Maryland ) and are about 60 million years old, an exact species assignment has not been made. Since then, hammerhead fossils, usually teeth, have been discovered around the world. Species that have only been described in fossil form and no longer exist today, mainly S. americana , S. gilmorei , S. laevissima , S. magna and S. prisca play a role. The oldest finds of S. prisca come from the Ypresium of Saudi Arabia (55.8 to 48.6 million years ago). Other finds that are assigned to this species come from North America, Europe and Africa and extend into the Pliocene (5.3 to 2.6 million years ago).
The oldest finds of a modern species that still exist today come from the bow-fronted hammerhead shark and are classified in the late Eocene (37.2 to 33.2 million years ago). The spoon-head hammerhead first appeared in fossils in the Chattium (28.4 to 23.03 million years ago), the great hammerhead shark in the early Miocene (23 to 16 million years ago).
Systematics
According to current knowledge, the family of hammerheads contains nine species, which are divided into two genera. It is a monotypic species of the genus Eusphyra and eight species of the genus Sphyrna :
| Genus Eusphyra Gill , 1861 - 1 Art | ||||||
| German name | Scientific name | distribution | Hazard level Red List of IUCN |
Remarks | image | |
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| Winged hammerhead shark |
Eusphyra blochii ( Cuvier , 1816) |
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 ( Near Threatened - potentially endangered, warning list)
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Maximum length 1.86 meters, lives mainly on flat seashores |
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| Genus Sphyrna Rafinesque , 1810 - 8 species | ||||||
| German name | Scientific name | distribution | Hazard level Red List of IUCN |
Remarks | image | |
| Corona hammerhead shark |
Sphyrna corona Springer , 1940 |
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( Near Threatened - potentially endangered, warning list)
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Maximum length 0.92 meters (smallest hammerhead shark), lives mainly on flat seashores | ||
| Bow-forehead hammerhead |
Sphyrna lewini ( Griffith & Smith , 1834) |
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 ( Endangered - endangered)
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Maximum length 3.70 to 4.20 meters, lives mainly in the pelagic region near the coast |
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| Spoonhead hammerhead shark |
Sphyrna media Springer , 1940 |
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 ( Data Deficient - insufficient data for a classification)
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Maximum length 1.50 meters, lives mainly on flat seashores | ||
| Great hammerhead shark |
Sphyrna mokarran ( Rüppell , 1837) |
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( Endangered - endangered)
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Maximum length 5.50 to 6.10 meters, lives mainly in the pelagic region near the coast |
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| Shovel-nosed hammerhead shark |
Sphyrna tiburo ( Linnaeus , 1758) |
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 ( Least Concern - not at risk)
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Maximum length 1.50 meters, lives mainly on flat seashores |
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| Small-eyed hammerhead shark |
Sphyrna tudes ( Valenciennes , 1822) |
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 ( Vulnerable - endangered)
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Maximum length 1.22 to 1.50 meters, lives mainly on shallow seashores |
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| Smooth hammerhead shark |
Sphyrna zygaena ( Linnaeus , 1758) |
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( Vulnerable - endangered)
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Maximum length 3.70 to 4.00 meters, lives mainly in the pelagic region near the coast |
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Sphyrna gilberti Quattro , Driggers , Grady , Ulrich & MA Roberts , 2013 |
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 ( Not Evaluated - not assessed)
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Maximum length unknown | |||
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Relationships among hammerheads according to Cavalcanti 2007
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Relationships among hammerheads according to Lim et al. 2010
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The white-fin hammerhead shark ( Sphyrna couardi ), which is listed as an independent species in older literature , has been assigned to the bow-forehead hammerhead shark since 1986, the scientific name is accordingly regarded as a synonym for this species.
Originally it was assumed that the broadening of the head developed gradually, with the spade-nosed shark ( Scoliodon laticaudus ) being regarded as a sister species to the hammerhead sharks within the requiem sharks . According to this idea, the shovel-nose hammerhead was the most original type of hammerhead, while the wingtip hammerhead with its very large cephalofoil was considered a strongly derived species.
On the basis of phylogenetic investigations of morphological and molecular biological characteristics ( isoenzymes and mitochondrial DNA ) it could be proven that the wingtip hammerhead is the most primitive species within the hammerheads and within the genus Sphyrna the species with a very large cephalofoil (great hammerhead, Smooth hammerhead and bow-forehead hammerhead) are to be regarded as particularly original. This suggests that within the hammerheads the large species with a large cephalofoil represent the original state and the smaller species with the narrower heads are derived from them. The position of the large species with particularly expansive cephalofoil could also be confirmed by further investigations in 2010, whereby the results regarding the relationships between the species differ slightly from the results of 2007. Associated with this, a change in the function of the cephalofoil is assumed, which is reflected in the way of life of hammerhead sharks: While a wide cephalofoil occurs mainly in free-swimming species of the pelagic and mainly acts as a hydrofoil, the smaller species with smaller cephalofoil live mainly in Close to the ground as well as in muddy coastal areas and use the equipment of the sensory organs, in particular the Lorenzini ampoules, to localize prey. Regarding height, Lim et al. 2010 due to their kinship hypothesis and the distribution of the species that the most original hammerheads were large species, from which both the small wingtip hammerhead and the smaller Sphyrna species are derived. In August 2013 the new hammerhead species Sphyrna gilberti was described. This taxon, discovered in 1967 in the waters off South Carolina , is morphologically almost identical to the bow-forehead hammerhead. Only a DNA analysis provided evidence that this is a new species.
Relationship with people
The great hammerheads such as the great hammerhead, the bow-forehead hammerhead and the smooth hammerhead are classified as potentially dangerous to humans. Encounters with divers and swimmers are comparatively frequent because of its coastal lifestyle. The number of unprovoked attacks is very low, however. In total, only 21 shark accidents have been documented for all hammerhead shark species of the genus Sphyrna , two of which were fatal. A precise assignment to certain species is usually not made, especially between the bow-fronted hammerhead shark and the great hammerhead shark ( Sphyrna zygaena ). The great hammerhead sharks are generally not aggressive towards divers, and they are usually rather shy; however, aggressive behavior has also been observed for the great and smooth hammerhead. All smaller hammerhead sharks are considered harmless to humans, accidents with these species are not known.
Use and catch
Hammerhead sharks, especially the larger species, are fished both commercially and in recreational fishing . They can be caught in the coastal area as well as on the high seas, using long lines as well as bottom and trawl nets. As with other large sharks, the large fins are especially popular in Asia as the basis of the well-known shark fin soup ; the mostly still living torso is very often thrown back into the sea after the fins have been removed, where it dies ( shark finning ). However, the meat of the animals and especially the skin ( shark leather ) are also used regularly, the liver oil is used to obtain vitamins and the remains are used to make fish meal .
In addition, there are regularly high numbers of bycatches in regions where hammerhead sharks are not hunted themselves , as the animals near the coast are usually associated with commercially highly sought-after and heavily fished species. Due to the very imprecise data on deep-sea fishing, however, there are no specific catch figures or information on population sizes and changes in the various species. Hammerhead sharks also regularly get caught in shark nets, which are stretched to protect bathing beaches, especially off the coasts of Australia and South Africa.
Threat and protection
The big hammerhead sharks are very sensitive to overfishing due to their rather small number of individuals and the long development period . A reliable recording of the stocks is very difficult, however, since only a few fisheries authorities separate the species of hammerhead sharks in their statistics. The International Union for Conservation of Nature and Natural Resources (IUCN) classifies the great and the bow- fronted hammerhead shark as "endangered" and the smooth hammerhead shark as "vulnerable". The small-eyed hammerhead shark is also endangered because it is under intense fishing pressure and, due to its low reproductive rate, is very susceptible to population decline. There are indications that the catch numbers of the small-eyed hammerhead shark off the island of Trinidad in the Caribbean Sea and northern Brazil have already declined significantly and that this can be taken as an indication of a population decline in its entire range. The other small species are considered not or not yet endangered (see table).
literature
- Leonard J. V. Compagno : Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part 2. Carcharhiniformes. FAO Species Catalog for Fishery Purposes. Volume 4, FAO Rome 1984; Pp. 538-547. 92-5-101383-7. ( Family Sphyrnidae Gill, 1872 )
- Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press , Princeton 2005 ISBN 0-691-12072-2 , pp. 322-326.
- Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean. Franckh-Kosmos, Stuttgart 2005, ISBN 3-440-10458-3 , pp. 213-223.
- Ralf M. Hennemann: Sharks & rays worldwide. Year Publishing House Hamburg 2001; Pp. 178-188. ISBN 3-86132-584-5 .
Individual evidence
- ^ A b Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press, Princeton 2005 ISBN 0-691-12072-2 , p. 325.
- ^ Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World. Princeton University Press, Princeton 2005 ISBN 0-691-12072-2 , p. 323.
- ^ A b c d Leonard J. V. Compagno: Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part 2. Carcharhiniformes. FAO Species Catalog for Fishery Purposes. Volume 4, FAO Rome 1984; Pp. 538-539. 92-5-101383-7. ( Family Sphyrnidae Gill, 1872 ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. )
- ↑ Castro, JI: The biology of the golden hammerhead, Sphyrna tudes , off Trinidad . In: Environmental Biology of Fishes . 24, No. 1, 1989, pp. 3-11. doi : 10.1007 / BF00001605 .
- ^ Ralf M. Hennemann: Haie & Rochen worldwide. Year Publishing House Hamburg 2001; Pp. 178-181. ISBN 3-86132-584-5 .
- ↑ Brandon R. Brown: Modeling an electrosensory landscape: behavioral and morphological optimization in elasmobranch prey capture. The Journal for Experimental Biology 205, 2002; Pp. 999-1007.
- ↑ DM McComb, TC Tricas, SM Kajiura: Enhanced visual fields in hammerhead sharks. The Journal for Experimental Biology 212, 2009; Pp. 4010-4018.
- ↑ Strong, WR, Snelson, Jr., FF, and Gruber, SH: Hammerhead Shark Predation on Stingrays: An Observation of Prey Handling by Sphyrna mokarran . In: American Society of Ichthyologists and Herpetologists (Eds.): Copeia . 1990, No. 3, September 19, 1990, pp. 836-840. doi : 10.2307 / 1446449 .
- ↑ Chapman, DD and Gruber, SH: A further observation of the prey-handling behavior of the great hammerhead shark, Sphyrna mokarran : predation upon the spotted eagle ray, Aetobatus narinari . . In: Bulletin of Marine Science . 70, No. 3, May 2002, pp. 947-952.
- ↑ a b c d Douglas D. Lim, Philip Motta, Kyle Mara, Andrew P. Martin: Phylogeny of hammerhead sharks (Family Sphyrnidae) inferred from mitochondrial and nuclear genes . In: Molecular Phylogenetics and Evolution . tape 55 , no. 2 , 2010, p. 572-579 .
- ↑ Stafford-Deitsch, J .: Red Sea Sharks . Trident Press Ltd, 1999, ISBN 1-900724-28-6 , pp. 92-93.
- ↑ Great Hammerhead . Elasmodiver.com . Retrieved on October 18, 2008.
- ^ A b c d Leonard J. V. Compagno: Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part 2. Carcharhiniformes. FAO Species Catalog for Fishery Purposes. Volume 4, FAO Rome 1984; Pp. 538-547. 92-5-101383-7. ( Family Sphyrnidae Gill, 1872 ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. )
- ↑ a b c d e f Cathleen Bester: Scalloped Hammerhead. In: Florida Museum of Natural History. Retrieved September 1, 2010 (English).
- ↑ a b c Alessandro de Maddalena, Harald Bänsch: Sharks in the Mediterranean. Franckh-Kosmos, Stuttgart 2005, ISBN 3-440-10458-3 , pp. 213-223.
- ↑ Cheryl D. Wylga, Philip J. Motta: Durophagy in sharks: Feeding mechanisms of the hammerhead Sphyrna tiburo. The Journal of Experimental Biology 203, 2000; Pp. 2781-2796.
- ↑ a b c L.JV Compagno: Sharks of the Order Carcharhiniformes. Princeton University Press 1988.
- ↑ Demian D. Chapman et al. a .: Virgin birth in a hammerhead shark . In: Biology Letters . tape 3 , no. 4 , 2007, p. 425-427 , doi : 10.1098 / rsbl.2007.0189 , PMC 2390672 (free full text).
- ↑ Kevin A. Feldheim, Demian D. Chapman, Doug Sweet, Seán Fitzpatrick, Paulo A. Prodöhl, Mahmood S. Shivji, Bob Snowden: Shark Virgin Birth Produces Multiple, Viable Offspring . In: Journal of Heredity . 101, No. 3, 2010, pp. 374-377. doi : 10.1093 / jhered / esp129 .
- ↑ Holtcamp, W .: Lone Parents: Parthenogenesis in Sharks . In: BioScience . 59, No. 7, July / August 2009, pp. 546-550. doi : 10.1525 / bio.2009.59.7.3 .
- ^ CR Eastman Pisces in CLARK, WB & MARTIN, GC The Eocene deposits of Maryland. Maryland Geological Survey, Stratigraphic Memoir 98-113, Baltimore 1901; Plates 12–15.
- ↑ a b Sphyrnidae in the Palaeobiology Database.
- ^ Leonard Compagno, Marc Dando, Sarah Fowler: Sharks of the World . Princeton University Press, Princeton 2005, ISBN 0-691-12072-2 , pp. 322-326 .
- ↑ Eusphyra blochii in the Red List of Threatened Species of the IUCN 2010. Posted by: Simpfendorfer, CA (SSG Australia & Oceania Regional Workshop, March 2003), 2003. Accessed on 19 September, 2010.
- ↑ Sphyrna corona in the endangered Red List species the IUCN 2010. Posted by: Mycock, SG (SSG South America Regional Workshop, June 2003), 2004. Accessed on 19 September, 2010.
- ↑ a b c Sphyrna lewini in the Red List of Threatened Species of the IUCN 2010. Posted by: J. Baum u. a., 2007. Retrieved September 19, 2010.
- ↑ Sphyrna media in the endangered Red List species the IUCN 2010. Posted by: Casper, BM & Burgess, GH, 2006. Retrieved on 19 September, 2010.
- ↑ a b Sphyrna mokarran in the Red List of Endangered Species of the IUCN 2010. Posted by: J. Denham u. a., 2007. Retrieved September 19, 2010.
- ↑ Sphyrna tiburo in the endangered Red List species the IUCN 2010. Posted by: Musick, JA & Fowler, SL (Shark Red List Authority), 2005. Accessed on 19 September, 2010.
- ↑ a b Sphyrna tudes in the endangered Red List species the IUCN 2010. Posted by: Mycock, SG, Lessa, R. & Almeida, Z., 2006. Retrieved on 19 September, 2010.
- ↑ a b Sphyrna zygaena in the Red List of Threatened Species of the IUCN 2010. Posted by: BM Caspar u. a., 2005. Retrieved September 15, 2010.
- ↑ a b Joseph M. Quattro, William B. Driggers, James M. Grady, Glenn F. Ulrich & Mark A. Roberts: Sphyrna gilberti sp. nov., a new hammerhead shark (Carcharhiniformes, Sphyrnidae) from the western Atlantic Ocean . In: Zootaxa 3702 (2): 159-178, 2013
- ↑ a b c Mauro José Cavalcanti: A Phylogenetic Supertree of the Hammerhead Sharks (Carcharhiniformes: Sphyrnidae) . In: Zoological Studies . tape 46 , no. 1 , 2007, p. 6–11 ( zoolstud.sinica.edu.tw [PDF; 175 kB ]).
- ↑ Among other things in: Leonard J. V. Compagno: Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part 2. Carcharhiniformes. In: FAO Species Catalog for Fishery Purposes . tape 4 . FAO, Rome 1984, ISBN 92-5101383-7 , Family Sphyrnidae Gill, 1872, p. 545-547 ( [1] [PDF]).
- ^ R. Aidan Martin: Recent Changes in Hammerhead Taxonomy. In: ReefQuest Center for Shark Research. February 24, 1998, accessed October 18, 2008 .
Web links
- Sphyrnidae on Fishbase.org (English)
- John F. Morrissey: Fact Sheet: Hammerhead Sharks. In: Shark Info. September 1, 1997
