Pycnodontiformes is an extinct order of primarily marine bony fish. The group first appeared during the

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

and disappeared during the

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...

. The group has been found in rock formations in Africa, Asia, Europe, North and South America. They were small to middle-sized fish, generally with laterally-compressed deep bodies, some with almost circular outlines, adapted for manuverability in reef-like environments. The group was morphologically diverse containing forms such the very short but deep

Gebrayelichthyidae Gebrayelichthyidae is a family of extinct pycnodontid fish, with a superficially shrimpfish-like appearance that lived during the lower Cenomanian. The family is composed of two genera, the type genus, '' Gebrayelichthys'', and the monotypic ...

and the horned ''

Ichthyoceros ''Ichthyoceros spinosus'' is an extinct pycnodontid that lived during the lower Cenomanian of what is now Lebanon. ''I. spinosus'' had a triple, forward-pointing horn-like spine between its eyes, very similar to the single spine of ''Trewavasia ...

,'' both from the early Late Cretaceous of Lebanon. Most, but not all members of the groups had jaws with round and flattened teeth, well adapted to crush food items (

durophagy Durophagy is the eating behavior of animals that consume hard-shelled or exoskeleton bearing organisms, such as corals, shelled mollusks, or crabs. It is mostly used to describe fish, but is also used when describing reptiles, including fossil tu ...

), such as echinoderms, crustaceans and molluscs. Some pyncodontiformes developed

piranha A piranha or piraña (, , or ; or , ) is one of a number of freshwater fish in the family Serrasalmidae, or the subfamily Serrasalminae within the tetra family, Characidae in order Characiformes. These fish inhabit South American rivers, fl ...

like teeth used for eating flesh. Most species inhabited shallow marine

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock o ...

environments, while a handful of species lived in freshwater or brackish conditions. While rare during the Triassic and Early-Middle Jurassic, Pycnodontiformes became abundant and diverse during the Late Jurassic, remaining diverse until a burst of diversification at the beginning of the Late Cretaceous, after which they began to gradually decline, with a more sudden decline at the end of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

due to the collapse of reef ecosystems, finally becoming extinct during the

Taxonomy

* Order Pycnodontiformes (Berg, 1937) ** Genus ?'' Acrorhinichthys'' Taverne & Capasso, 2015 ** Genus ?'' Archaeopycnodon'' Sanchez & Benedetto, 1980 ** Genus ?''

Athrodon ''Athrodon'' is an extinct genus of pycnodontid that lived in shallow seas in what is now England and France from the Late Jurassic until the genus extinction during the start of the late Cretaceous. The various species are very similar in spl ...

'' le Sauvage 1880 non Osborn, 1887 ** Genus ?'' Callodus'' Thurmond, 1974 ** Genus ?'' Cosmodus'' le Sauvage, 1879 'Glossodus''_Costa,_1851_non_Agassiz,_1828_ex_Spix_&_Agassiz,_1829_non_McCoy,_1848.html" ;"title="Glossodus.html" ;"title="'Glossodus">'Glossodus'' Costa, 1851 non Agassiz, 1828 ex Spix & Agassiz, 1829 non McCoy, 1848">Glossodus.html" ;"title="'Glossodus">'Glossodus'' Costa, 1851 non Agassiz, 1828 ex Spix & Agassiz, 1829 non McCoy, 1848** Genus ?''Ellipsodus'' Cornuel, 1877 ** Genus ?''Grypodon'' Hay, 1899 [''Ancistrodon'' Dames, 1883 non De Beauvois, 1799 non Roemer, 1852 non Wagler, 1830] ** Genus ?''[ ercediella'' Koerber, 2012 'Camposichthys''_Figueiredo_&_Silva-Santos,_1991_non_Travassos,_1946_non_Whitley,_1953.html" ;"title="Camposichthys.html" ;"title="'Camposichthys">'Camposichthys'' Figueiredo & Silva-Santos, 1991 non Travassos, 1946 non Whitley, 1953">Camposichthys.html" ;"title="'Camposichthys">'Camposichthys'' Figueiredo & Silva-Santos, 1991 non Travassos, 1946 non Whitley, 1953**Genus ?''Piranhamesodon'' Kölbl-Ebert ''et al.'', 2018 ** Genus ?''Pseudopycnodus'' Taverne, 2003 ** Genus ?''Tergestinia'' Capasso, 2000 ** Genus ?''Thurmondella'' Thurmond, 1974 non 'Paramicrodon''_Thurmond,_1974_non_de_Meijere,_1913.html" ;"title="Paramicrodon.html" ;"title="'Paramicrodon">'Paramicrodon'' Thurmond, 1974 non de Meijere, 1913">Paramicrodon.html" ;"title="'Paramicrodon">'Paramicrodon'' Thurmond, 1974 non de Meijere, 1913** Genus ?''Uranoplosus'' le Sauvage, 1879 ** Genus ?''Woodthropea'' Swinnerton, 1925 **Family ?Hadrodontidae Thurmond & Jones, 1981 *** Genus ''Hadrodus'' Leidy, 1858 'Propenser''_Applegate,_1970.html" ;"title="Propenser.html" ;"title="'Propenser">'Propenser'' Applegate, 1970">Propenser.html" ;"title="'Propenser">'Propenser'' Applegate, 1970**Family ?

Nursall & Capasso, 2004 *** Genus ''Gebrayelichthys'' Nursall & Capasso, 2004 *** Genus ''Maraldichthys'' Taverne & Capasso, 2014 **Family ?Gladiopycnodontidae Taverne & Capasso, 2013 *** Genus '' Arduafrons'' Frickhinger, 1991 *** Genus '' Eomesodon'' Woodward, 1918 *** Genus '' Gladiopycnodus'' Taverne & Capasso, 2013 *** Genus '' Joinvillichthys'' Taverne & Capasso, 2014 ** Genus '' Micropycnodon'' Hibbard & Graffham, 1945 'Pycnomicrodon''_Hibbard_&_Graffham,_1941_non_Hay,_1916.html" ;"title="Pycnomicrodon.html" ;"title="'Pycnomicrodon">'Pycnomicrodon'' Hibbard & Graffham, 1941 non Hay, 1916">Pycnomicrodon.html" ;"title="'Pycnomicrodon">'Pycnomicrodon'' Hibbard & Graffham, 1941 non Hay, 1916*** Genus ''Monocerichthys'' Taverne & Capasso, 2013 *** Genus ''Pankowskichthys'' Taverne & Capasso, 2014 *** Genus ''Paramesturus'' Taverne, 1981 *** Genus ''Rostropycnodus'' Taverne & Capasso, 2013 *** Genus '' Stenoprotome'' Hay, 1903 **Family Mesturidae Nursall, 1996 *** Genus ''

Mesturus Mesturus is an extinct genus of ray-finned fish from the 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 Pe ...

'' Wagner, 1862 **Family Gyrodontidae Berg, 1940 *** Genus ''

Gyrodus ''Gyrodus'' (from el, γύρος , 'curved' and el, ὀδούς 'tooth') is an extinct genus of pycnodontiform ray-finned fish that lived from the late Triassic ( Rhaetian) to the middle Cretaceous ( Cenomanian). Distribution Fossils of ...

'' Agassiz, 1833 **Family Brembodontidae Tintori, 1981 rembodidae; Gibbodontidae Tintori, 1981*** Genus ''

Brembodus ''Brembodus'' is an extinct pycnodontid, the type genus of the family Brembodontidae. ''G. cenensis'' fossils are known from the Late Triassic strata of Cene, Italy. See also * '' Gibbodon'' * Pycnodontiformes * Prehistoric fish * List of pre ...

'' Tintori, 1981 *** Genus ''

Gibbodon ''Gibbodon cenensis'' is an extinct pycnodontid of the family Brembodontidae. ''G. cenensis'' fossils are known from the Late Triassic strata of Cene, Italy. It lived sympatrically with its close relative, ''Brembodus''. See also * Pycnodon ...

'' Tintori, 1981 **Family Coccodontidae Berg, 1940 rewavasiidae Nursall, 1996 *** Genus ''

Coccodus ''Coccodus'' is an extinct genus of extinct pycnodontid fish that lived during the lower Cenomanian. The various species had a pair of massive, curved spines emanating from the lower sides of the head, and one curved spine on the top of its hea ...

'' Pictet, 1850 *** Genus ''

Corusichthys ''Corusichthys megacephalus'' is an extinct pycnodontid that lived during the lower Cenomanian of what is now Lebanon. ''C. megacephalus'' is known from a 34 mm long fossil. It had plates arranged like a helmet around its head, and had a m ...

'' Taverne & Capasso, 2014 *** Genus ''

Hensodon ''Hensodon spinosus'' is an extinct pycnodontid that lived during the Upper Cenomanian of what is now Lebanon. ''H. spinosus'' superficially resembled a marine angelfish with a massive head, and a very spiny pectoral girdle. Different specimens ...

'' Kriwet, 2004 *** Genus ''

'' Gayet, 1984 *** Genus '' Paracoccodus'' Taverne & Capasso, 2014 *** Genus ''

Trewavasia ''Trewavasia carinata'' is an extinct pycnodontid fish in the family Coccodontidae that lived during the lower Cenomanian of what is now Lebanon Lebanon ( , ar, لُبْنَان, translit=lubnān, ), officially the Republic of Lebanon () o ...

'' White & Moy-Thomas, 1941 'Xenopholis''_Davis,_1887_non_Peters,_1869;_''Xenopholoides.html" ;"title="Xenopholis.html" ;"title="'Xenopholis">'Xenopholis'' Davis, 1887 non Peters, 1869; ''Xenopholoides">Xenopholis.html" ;"title="'Xenopholis">'Xenopholis'' Davis, 1887 non Peters, 1869; ''Xenopholoides'' Fowler, 1958] **Family Pycnodontidae Agassiz, 1833 corrig. Bonaparte, 1845 [Nursalliidae Bloy, 1987; Sphaerodontidae Giebel, 1846; Palaeobalistidae Blot, 1987; Proscinetidae Gistel, 1848; Gyronchidae] *** Genus '' Abdobalistum'' Poyato-Ariza & Wenz, 2002 *** Genus '' Anomiophthalmus'' Costa, 1856 *** Genus '' Anomoedus'' Forir, 1887 *** Genus '' Acrotemnus'' Agassiz 1836, *** Genus '' Akromystax'' Poyato-Ariza & Wenz, 2005 *** Genus '' Coelodus'' Heckel, 1854 *** Genus '' Flagellipinna'' Cawley & Kriwet, 2019 *** Genus '' Macropycnodon'' Shimada, Williamson & Sealey, 2010 *** Genus '' Macromesodon'' Blake 1905 non Lehman, 1966 'Mesodon''_Wagner,_1851_non_Rafinesque,_1821;_''Gyronchus.html" ;"title="Mesodon.html" ;"title="'Mesodon">'Mesodon'' Wagner, 1851 non Rafinesque, 1821; ''Gyronchus">Mesodon.html" ;"title="'Mesodon">'Mesodon'' Wagner, 1851 non Rafinesque, 1821; ''Gyronchus'' Agassiz, 1839; ''Apomesodon'' Poyato-Ariza & Wenz, 2002] *** Genus ''Neoproseinetes'' De Figueiredo & Silva Santos, 1990 *** Genus ''Nursallia'' Blot, 1987 *** Genus ''Ocloedus'' Poyato-Ariza & Wenz, 2002 *** Genus '' Oropycnodus'' Poyato-Ariza & Wenz, 2002 *** Genus '' Palaeobalistum'' Taverne ''et al.'', 2015 *** Genus '' Paranursallia'' Taverne ''et al.'', 2015 *** Genus '' Phacodus'' Dixon, 1850 *** Genus '' Polazzodus'' Poyoto-Ariza, 2010 *** Genus '' Polygyrodus'' White, 1927 *** Genus '' Potiguara'' Machado & Brito, 2006 *** Genus '' Proscinetes'' Gistl, 1848

Microdon Hover flies (family Syrphidae) of the genus ''Microdon'' are unusual among the Diptera. Like other members of the subfamily, they are myrmecophiles, meaning they inhabit the nests of ants. There are 249 species known worldwide, with the great ...

'' Agassiz, 1833 non Meigen, 1803 non Fritsch, 1876 non Conrad, 1842 non Gistl, 1848 non Dixon, 1850; ''Polypsephis'' Hay, 1899] *** Genus ''Pycnomicrodon'' Hay 1916 non Hibbard & Graffham, 1941 *** Genus ''Pycnodus'' Agassiz, 1833 *** Genus ''Rhinopycnodus'' Taverne & Capasso, 2013 *** Genus '' Sphaerodus'' Agassiz, 1833 *** Genus '' Sphaeronchus'' Stinton & Torrens, 1967 *** Genus '' Stenamara'' Poyato-Ariza & Wenz, 2000 *** Genus '' Stemmatias'' Hay, 1899 'Stemmatodus''_St._John_&_Worthen,_1875_non_Heckel,_1854_non.html" ;"title="Stemmatodus.html" ;"title="'Stemmatodus">'Stemmatodus'' St. John & Worthen, 1875 non Heckel, 1854 non">Stemmatodus.html" ;"title="'Stemmatodus">'Stemmatodus'' St. John & Worthen, 1875 non Heckel, 1854 non*** Genus ''Stemmatodus'' Heckel, 1854 non St. John & Worthen, 1875 non *** Genus ''Sylvienodus'' Poyato-Ariza & Wenz, 2013 *** Genus ''Tamanja'' Wenz, 1989 *** Genus '' Tepexichtys'' Applegate, 1992 *** Genus '' Tibetodus'' Young & Liu, 1954 *** Genus '' Turbomesodon'' Poyato-Ariza & Wenz, 2004 Macromesodon''_Lehman,_1966_non_Blake,_1905.html" ;"title="' Macromesodon'' Lehman, 1966 non Blake, 1905">' Macromesodon'' Lehman, 1966 non Blake, 1905*** Genus '' Typodus'' Quenstedt, 1858 *** Genus '' Abdobalistum'' Poyato-Ariza & Wenz, 2002 **Family ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' *** Genus '' Agassizilia'' Cooper and Martill, 2020 *** Genus '' Neomesturus'' Cooper and Martill, 2020Cooper, S.L.A. and Martill, D.M. (2020). "Pycnodont fishes (Actinopterygii: Pycnodontiformes) from the Upper Cretaceous (lower Turonian) Akrabou Formation of Asfla, Morocco" Cretaceous Research 116, 104607

References

** Capasso, Luigi (2021). "Pycnodonts: An overwiew and new insights in the Pycnodontomorpha Nursall, 2010". Occasional Paper of the University Museum of Chieti, Monographic Publication, 1: 1-223. {{Taxonbar, from=Q1787823 Prehistoric ray-finned fish orders