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The Hexanchiformes are the
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
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 Selachi ...
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 geologic period and 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 Jurassic constitutes the middle period of ...
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 c ...
, 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 co ...
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, wh ...
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 cont ...
and
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
, 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 Paleo ...
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 n ...
. 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 to have survived after the Permian extinction (and by extension, the oldest extant order of elasmobranchs). The frilled sharks of the genus ''Chlamydoselachus'' are very different from the cow sharks, 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 s ...
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 pl ...
1884
(frilled sharks) **''
Chlamydoselachus ''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 s ...
''
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 pl ...
, 1884
***'' Chlamydoselachus africana'' Ebert & Compagno, 2009 (Southern African frilled shark) *** '' Chlamydoselachus anguineus''
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 pl ...
, 1884
(frilled shark) *Family Hexanchidae J. E. Gray 1851 (cow sharks) **'' Heptranchias''
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'' ( Bonnaterre, 1788) (sharpnose sevengill shark) ** ''
Hexanchus The sixgill sharks are a genus, ''Hexanchus'', of deepwater sharks in the family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purp ...
''
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
***'' Hexanchus griseus ''( Bonnaterre, 1788) (bluntnose sixgill shark) *** '' Hexanchus nakamurai''
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 ''Daly-Engel, 2018 (Atlantic sixgill shark) ** '' Notorynchus'' Ayres, 1855 ***''
Notorynchus cepedianus The broadnose sevengill shark (''Notorynchus cepedianus'') is the only extant member of the genus ''Notorynchus'', in the family Hexanchidae. It is recognizable because of its seven gill slits, while most shark species have five gill slits, with ...
''( Péron, 1807) (broadnose sevengill shark)


Extinct 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 s ...
**''
Chlamydoselachus ''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 s ...
''
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 pl ...
, 1884
***''
Chlamydoselachus bracheri ''Rolfodon bracheri'' is an extinct species from the family Chlamydoselachidae. It lived during the Miocene. ''R. bracheri'' was named by Pfeil in 1983. Originally it was described as a species belonging to the genus ''Chlamydoselachus ''Chl ...
'' 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 Crassodontidanidae is a family of extinct cow sharks that lived from the Early Jurassic to the Early Cretaceous. It contains three genera: ''Crassodontidanus ''Crassodontidanus'' is an extinct genus of sharks and the sole member of the family ...
**''
Crassodontidanus ''Crassodontidanus'' is an extinct genus of sharks and the sole member of the family Crassodontidanidae, in the order Hexanchiformes The Hexanchiformes are the order consisting of the most primitive types of sharks, and numbering just seve ...
'' Kriwet & Klug, 2011 ***''Crassodontidanus serratus'' Fraas, 1855 *** ''Crassodontidanus wiedenrothi'' Thies, 1983 ** ''Notidanoides'' Maisey, 1986 ***''Notidanoides muensteri''
Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 1843
** ''Notidanus''
Cuvier Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in nat ...
, 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'' Underwood, Goswami, Prasad, Verma & Flynn, 2011 ***''Gladioserratus aptiensis'' Pictet, 1864 *** ''Gladioserratus dentatus'' Guinot, Cappetta & Adnet, 2014 *** ''Gladioserratus magnus'' Underwood, Goswami, Prasad, Verma & Flynn, 2011 ** '' Heptranchias''
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 ezoensis'' Applegate & Uyeno, 1968 *** ''Heptranchias howellii'' Reed, 1946 *** ''Heptranchias karagalensis'' Kozlov in Zhelezko & Kozlov, 1999 *** ''Heptranchias tenuidens'' Leriche, 1938 ** ''
Hexanchus The sixgill sharks are a genus, ''Hexanchus'', of deepwater sharks in the family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purp ...
''
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
***''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 Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 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 Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 1843
** '' Notorynchus'' Ayres, 1855 ***''Notorynchus borealus'' Jordan & Hannibal, 1923 *** ''Notorynchus kempi'' Ward, 1979 *** ''Notorynchus lawleyi'' Cigala Fulgosi, 1983 *** ''Notorynchus primigenius''
Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 1843
*** ''Notorynchus serratissimus''
Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 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 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 shar ...
'' 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'' is an extinct genus of sharks and the sole member of the family Mcmurdodontidae, in the order Hexanchiformes The Hexanchiformes are the order consisting of the most primitive types of sharks, and numbering just seven extant sp ...
? **'' 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, ...
**''Occitanodus'' Guinot, Cappetta & Adnet, 2014 ***''Occitanodus sudrei'' Guinot, Cappetta & Adnet, 2014 ** ''Orthacodus'' Woodward, 1889 ***''Orthacodus longidens''
Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 1843
** ''Sphenodus''
Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 1843
***''Sphenodus alpinus'' Gümbel, 1861 *** ''Sphenodus longidens''
Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 1843
*** ''Sphenodus lundgreni'' Davis, 1890 *** ''Sphenodus macer'' Quenstedt, 1852 *** ''Sphenodus nitidus'' Wagner, 1862 *** ''Sphenodus planus''
Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he rec ...
, 1843
*** ''Sphenodus rectidens'' Emmons, 1858 *** ''Sphenodus robustidens'' Seguenza, 1900 *** ''Sphenodus tithonius'' Gemmellaro, 1871 *** ''Sphenodus virgai'' Gemmellaro, 1871


Species


See also

* Time range of Hexanchiformes 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