The Hexanchiformes are the order consisting of the most primitive types of

shark Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimo ...

s, and numbering just seven extant species.

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

sharks that were apparently very similar to modern sevengill species are known from

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

specimens. Hexanchiform sharks have only one

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

, either six or seven

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

s, and no

nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. All ...

in the eyes. Shark teeth similar to those modern hexanchids are known from

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

deposits in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

and

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

, as well as

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

deposits in

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. If these are in fact hexanchids, this may be the only

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

order of

elasmobranchs Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). Members of this subclass are characterised by having five to seven pairs of gil ...

to have survived after the

Permian extinction The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleozo ...

(and by extension, the oldest extant order of elasmobranchs). The frilled sharks of the genus ''Chlamydoselachus'' are very different from the

cow shark Cow sharks are a shark family, the Hexanchidae, characterized by an additional pair or pairs of gill slits. Its 37 species are placed within the 10 genera: '' Gladioserratus'', '' Heptranchias'', ''Hexanchus'', ''Notidanodon'', '' Notorynchus'', ...

s, and have been proposed to be moved to a distinct order, Chlamydoselachiformes.

Classification

Living species

*Family

Chlamydoselachidae ''Chlamydoselachus'' is a genus of sharks and the sole extant member of the family Chlamydoselachidae, in the order Hexanchiformes. It contains two extant and several extinct species. The most widely known species still surviving is the frilled ...

Garman Garman is a surname or first name. Notable people with the name include: Sports * Ann Garman, All-American Girls Professional Baseball League player * Judi Garman (born 1954), American softball coach * Mike Garman (born 1949), American baseball pla ...

1884 (frilled sharks) **''

Chlamydoselachus ''Chlamydoselachus'' is a genus of sharks and the sole extant member of the family (biology), family Chlamydoselachidae, in the order (biology), order Hexanchiformes. It contains two extant and several extinct species. The most widely known speci ...

, 1884 ***'' Chlamydoselachus africana'' Ebert & Compagno, 2009 (Southern African frilled shark) *** '' Chlamydoselachus anguineus''

, 1884 (frilled shark) *Family Hexanchidae

J. E. Gray John Edward Gray, Fellow of the Royal Society, FRS (12 February 1800 – 7 March 1875) was a British zoology, zoologist. He was the elder brother of zoologist George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray ...

1851 (cow sharks) **''

Heptranchias ''Heptranchias'' is a genus of sharks in the family Cow shark, Hexanchidae. Species *''Sharpnose sevengill shark, Heptranchias perlo'' (Pierre Joseph Bonnaterre, Bonnaterre, 1788) (sharpnose sevengill shark) *†''Heptranchias ezoensis'' Appl ...

Rafinesque Constantine Samuel Rafinesque-Schmaltz (; October 22, 1783September 18, 1840) was a French 19th-century polymath born near Constantinople in the Ottoman Empire and self-educated in France. He traveled as a young man in the United States, ultimat ...

, 1810 *** ''

Heptranchias perlo The sharpnose sevengill shark (''Heptranchias perlo''), also known as one-finned shark, perlon shark, sevengill cow shark, sharpsnouted sevengill or slender sevengill, is a species of shark in the family Hexanchidae, and the only living species ...

'' ( Bonnaterre, 1788) (sharpnose sevengill shark) ** ''

Hexanchus The sixgill sharks are a genus, ''Hexanchus'', of deepwater sharks in the family Hexanchidae. These sharks are characterized by a broad, pointed head, six pairs of gill slits, comb-like, yellow lower teeth, and a long tail. The largest species ca ...

, 1810 ***''

Hexanchus griseus The bluntnose sixgill shark (''Hexanchus griseus''), often simply called the cow shark, is the largest hexanchoid shark, growing to in length. It is found in tropical and temperate waters worldwide and its diet is widely varied by region. The ...

''( Bonnaterre, 1788) (bluntnose sixgill shark) *** ''

Hexanchus nakamurai The bigeyed sixgill shark (''Hexanchus nakamurai'') is a cow shark of the family Hexanchidae. Its dorsal surface has a brownish-gray color, and is sharply separated from the light coloring of its ventral surface. The eyes are a fluorescent gre ...

Teng Teng may refer to: *Teng (surname) (滕), a Chinese surname *Teng (state), an ancient Chinese state *Teng (mythology), a flying dragon in Chinese mythology *Teng County Teng County or Tengxian (; za, Dwngz Yen) is a county of eastern Guangxi, C ...

, 1962 (bigeyed sixgill shark) *** ''

Hexanchus vitulus The Atlantic sixgill shark (''Hexanchus vitulus'') is a rare species of hexanchid shark found in the Atlantic Ocean. It was formerly described as its own species, but was synonymised with the bigeye sixgill shark The bigeyed sixgill shark ( ...

''Daly-Engel, 2018 (Atlantic sixgill shark) ** ''

Notorynchus ''Notorynchus'' is a genus of deepwater sharks in the family Hexanchidae. There is one extant species. Extant species * Broadnose sevengill shark (''Notorynchus cepedianus'') Péron, 1807 Extinct species * '' Notorynchus borealus'' Jordan & ...

'' Ayres, 1855 ***'' Notorynchus cepedianus ''( Péron, 1807) (broadnose sevengill shark)

Extinct species

*Family

**''

, 1884 ***'' Chlamydoselachus bracheri'' Pfeil, 1983 *** ''Chlamydoselachus fiedleri'' Pfeil, 1983 *** ''Chlamydoselachus garmani'' Welton, 1983 *** ''Chlamydoselachus goliath'' Antunes & Cappetta, 2002 *** ''Chlamydoselachus gracilis'' Antunes & Cappetta, 2002 *** ''Chlamydoselachus keyesi'' Mannering & Hiller, 2008 *** ''Chlamydoselachus landinii'' Carrillo-Briceño, Aguilera & Rodriguez, 2014 *** ''Chlamydoselachus lawleyi'' Davis, 1887 *** ''Chlamydoselachus tatere'' Consoli, 2008 *** ''Chlamydoselachus thomsoni'' Richter & Ward, 1990 *** ''Chlamydoselachus tobleri'' Leriche, 1929 *Family Crassodontidanidae **'' Crassodontidanus'' Kriwet & Klug, 2011 ***''Crassodontidanus serratus'' Fraas, 1855 *** ''Crassodontidanus wiedenrothi'' Thies, 1983 ** ''Notidanoides'' Maisey, 1986 ***''Notidanoides muensteri'' Agassiz, 1843 ** ''Notidanus'' Cuvier, 1816 ***''Notidanus amalthei'' Oppel, 1854 *** ''Notidanus atrox'' Ameghino, 1899 *** ''Notidanus intermedius'' Wagner, 1862 *** ''Notidanus nikitini'' Chabakov & Zonov, 1935 ** ''Pachyhexanchus'' Cappetta, 1990 ***''Pachyhexanchus pockrandti'' Ward & Thies, 1987 *Family Hexanchidae **''

Gladioserratus ''Gladioserratus'' is an extinct genus of cow shark. It contains three species: *'' Gladioserratus aptiensis'' Pictet, 1865 *'' Gladioserratus magnus'' Underwood, Goswami, Prasad, Verma & Flynn, 2011 *'' Gladioserratus dentatus'' Guinot, Cappet ...

'' Underwood, Goswami, Prasad, Verma & Flynn, 2011 ***''Gladioserratus aptiensis'' Pictet, 1864 *** ''Gladioserratus dentatus'' Guinot, Cappetta & Adnet, 2014 *** ''Gladioserratus magnus'' Underwood, Goswami, Prasad, Verma & Flynn, 2011 ** ''

, 1810 ***''Heptranchias ezoensis'' Applegate & Uyeno, 1968 *** ''Heptranchias howellii'' Reed, 1946 *** ''Heptranchias karagalensis'' Kozlov in Zhelezko & Kozlov, 1999 *** ''Heptranchias tenuidens'' Leriche, 1938 ** ''

, 1810 ***''Hexanchus agassizi'' Cappetta, 1976 *** ''Hexanchus andersoni'' Jordan, 1907 *** ''Hexanchus casieri'' Kozlov, 1999 *** '' Hexanchus collinsonae'' Ward, 1979 *** ''Hexanchus gracilis'' Davis, 1887 *** ''Hexanchus hookeri'' Ward, 1979 *** ''Hexanchus microdon'' Agassiz, 1843 *** ''Hexanchus tusbairicus'' Kozlov in Zhelezko & Kozlov, 1999 ** ''Notidanodon'' Cappetta, 1975 ***''Notidanodon brotzeni'' Siverson, 1995 *** ''Notidanodon dentatus'' Woodward, 1886 *** ''Notidanodon lanceolatus'' Woodward, 1886 *** ''Notidanodon loozi'' Vincent, 1876 *** ''Notidanodon pectinatus'' Agassiz, 1843 ** ''

'' Ayres, 1855 ***''Notorynchus borealus'' Jordan & Hannibal, 1923 *** ''Notorynchus kempi'' Ward, 1979 *** ''Notorynchus lawleyi'' Cigala Fulgosi, 1983 *** ''Notorynchus primigenius'' Agassiz, 1843 *** ''Notorynchus serratissimus'' Agassiz, 1843 *** ''Notorynchus subrecurvus'' Oppenheimer, 1907 ** ''Pachyhexanchus'' Cappetta, 1990 ***''Pachyhexanchus pockrandti'' Ward & Thies, 1987 ** ''Paraheptranchias'' Pfeil, 1981 ***''Paraheptranchias repens'' Probst, 1879 ** ''Pseudonotidanus'' Underwood & Ward, 2004 ***''Pseudonotidanus semirugosus'' Underwood & Ward, 2004 ** ''

Welcommia ''Welcommia'' is an extinct genus of shark. It contains only two species - ''Welcommia bodeuri'' and ''Welcommia cappettai'', described from the middle Oxfordian of Germany Germany,, officially the Federal Republic of Germany, is a ...

'' Cappetta, 1990 ***''Welcommia bodeuri'' Cappetta, 1990 *** '' Welcommia cappettai'' Klug & Kriwet, 2010 ** ''Weltonia'' Ward, 1979 ***''Weltonia ancistrodon'' Arambourg, 1952 *** ''Weltonia burnhamensis'' Ward, 1979 *Family Mcmurdodontidae ? **'' Mcmurdodus'' White, 1968 ***''Mcmurdodus featherensis'' White, 1968 *** ''Mcmurdodus whitei'' Turner, & Young, 1987 *Family

Orthacodontidae Orthacodontidae is an extinct family of sharks in the order Synechodontiformes. It contains twelve species within three genera. Some authors included it into Hexanchiformes or Lamniformes. Species * '' Occitanodus'' Guinot, Cappetta & Adnet, 20 ...

**''Occitanodus'' Guinot, Cappetta & Adnet, 2014 ***''Occitanodus sudrei'' Guinot, Cappetta & Adnet, 2014 ** ''Orthacodus'' Woodward, 1889 ***''Orthacodus longidens'' Agassiz, 1843 ** ''Sphenodus'' Agassiz, 1843 ***''Sphenodus alpinus'' Gümbel, 1861 *** ''Sphenodus longidens'' Agassiz, 1843 *** ''Sphenodus lundgreni'' Davis, 1890 *** ''Sphenodus macer'' Quenstedt, 1852 *** ''Sphenodus nitidus'' Wagner, 1862 *** ''Sphenodus planus'' Agassiz, 1843 *** ''Sphenodus rectidens'' Emmons, 1858 *** ''Sphenodus robustidens'' Seguenza, 1900 *** ''Sphenodus tithonius'' Gemmellaro, 1871 *** ''Sphenodus virgai'' Gemmellaro, 1871

Species

Footnotes

References

External links

* (Fish Base family reference) * (Fish Base family reference) {{Taxonbar, from=Q133317 Extant Middle Jurassic first appearances Cartilaginous fish orders Taxa named by Fernando de Buen y Lozano