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 (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

and disappeared during the

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

. 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, though the group was morphologically diverse. Most, but not all members of the groups had jaws with round and flattened teeth, well adapted to crush food items ( durophagy), such as echinoderms, crustaceans and molluscs. Some pycnodontiformes developed piranha 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 component, abiotic (non-living) processes such as deposition (geol ...

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, exhibiting a high but relatively static diversity during the Early Cretaceous. At the beginning of the Late Cretaceous they reached their apex of morphological and species diversity (much of this due to fossils found in the Sannine Formation of Lebanon, such as Gebrayelichthyidae and '' Ichthyoceros''), 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 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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

. They are considered to belong to the Neopterygii, but their relationship to other members of that group is uncertain.

Evolution and diversity

Pycnodontiforms first appeared in the

, alongside other successful groups of early neopterygians such as dapediiforms. A contributor for this early radiation of neopterygians was their effectiveness at adapting to different diets. Pycnodonts from the Late Triassic Zorzino Limestone in

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

had short and stout jaws with big crushing teeth for eating hard-shelled prey, while other actinopterygians like saurichthyids and birgeriids mainly occupied top predator piscivorous niches. They originated from marine habitats, specializing for manoeuverability in reef environments, but developed a variety of adaptations during the

Mesozoic The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

that enable them to pursue new diets and habitats, such as

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

and freshwaters. Only a few species adapted for open waters, like those of the family Gyrodontidae. In the Western Tethys, pycnodonts have always had a high species diversity. This stable environment, alongside its favorable climate conditions, supported the dispersal patterns within basal pycnodontids. They evolved such different jaw structures to avoid potential competition with other groups of durophagous neopterygians, such as the Dapediiformes and the Ginglymodi. Furthermore, their improved jaw performance also differentiated the pycnodonts from these neopterygians in that they allowed them to feed on tougher prey, while their increase in size allowed them to prey on larger items or specialise on a few species. Their families also differentiated amongst themselves in body and jaw shape, implying that they were more diverse in diet and habitat than previously thought. The fossil record of pycnodonts spans 175 million years, from the Triassic to the

, existing longer than non-avian dinosaurs. Their early record is incomplete, having only three genera from the Late Triassic, all with complete specimens. Whereas from the Early to Mid-

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 143.1 Mya. ...

there are only isolated teeth and jaws, and rarely a few exceptions for better, but still incomplete, fossils. By the

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

Pycnodontiforms became more common in the fossil record, a fact that relates to the presence of Lagerstätten, providing articulated fossils. This growth continues and, by the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, they experience a peak in diversity during the

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

. They were severely struck by the K/Pg Extinction and afterwards their diversity shrunk, having never achieved pre-extinction levels of diversity, eventually going extinct by the Late Eocene (

Priabonian The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage ...

Taxonomy

* Order Pycnodontiformes (Berg, 1937) ** Genus ?'' Acrorhinichthys'' Taverne & Capasso, 2015 ** Genus ?'' Archaeopycnodon'' Sanchez & Benedetto, 1980 ** Genus '' Arduafrons'' Frickhinger, 1991 ** Genus ?'' Athrodon'' le Sauvage 1880 non Osborn, 1887 ** Genus ?'' Callodus'' Thurmond, 1974 ** Genus ?'' Ellipsodus'' Cornuel, 1877 ** Genus '' Eomesodon'' Woodward, 1918 ** Genus ?'' Grypodon'' Hay, 1899 'Ancistrodon'' Dames, 1883 non De Beauvois, 1799 non Roemer, 1852 non Wagler, 1830** Genus ?'' Mercediella'' Koerber, 2012 '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 ''Paramesturus'' Taverne, 1981 **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">Paramicrodon.html" ;"title="'Paramicrodon">'Paramicrodon'' Thurmond, 1974 non de Meijere, 1913** Genus ?''Uranoplosus'' le Sauvage, 1879 ** Genus ?''Woodthropea'' Swinnerton, 1925 **Family Brembodontidae Tintori, 1981 [Brembodidae; Gibbodontidae Tintori, 1981] *** Genus '' Brembodus'' Tintori, 1981 *** Genus '' Gibbodon'' Tintori, 1981 **Family ? Hadrodontidae Thurmond & Jones, 1981 *** Genus '' Hadrodus'' Leidy, 1858 'Propenser'' Applegate, 1970">Propenser.html" ;"title="'Propenser">'Propenser'' Applegate, 1970**Family Gyrodontidae Berg, 1940 *** Genus ''Gyrodus'' Agassiz, 1833 **Family Mesturidae Nursall, 1996 *** Genus ''Mesturus'' Wagner, 1862 **Family

Pycnodontidae Pycnodontidae is an extinct family of ray-finned fishes, ranging from the Jurassic period until the Late Eocene. It was the largest and most derived family of the successful Mesozoic fish order Pycnodontiformes, and one of only two families (alon ...

Agassiz, 1833 corrig. Bonaparte, 1845 ursalliidae Bloy, 1987; Sphaerodontidae Giebel, 1846; Palaeobalistidae Blot, 1987; Proscinetidae Gistel, 1848; Gyronchidaeimg title="Neoproscinetes penalvai"; style="text-decoration: none; height:150px;float: left; padding: 0px 3px 0px 0px;"src="https://upload.wikimedia.org/wikipedia/commons/a/a8/Neoproscinetes_penalvai.JPG" > *** Genus '' Abdobalistum'' Poyato-Ariza & Wenz, 2002 *** Genus '' Acrotemnus'' Agassiz, 1843 (='' Macropycnodon'' Shimada, Williamson & Sealey, 2010) *** Genus ?'' Agassizilia'' Cooper & Martill, 2020 *** Genus '' Agoultpycnodus'' Taverne & Capasso, 2021 *** Genus '' Akromystax'' Poyato-Ariza & Wenz, 2005 *** Genus '' Anomiophthalmus'' Costa, 1856 *** Genus '' Anomoeodus'' Forir, 1887 *** Genus '' Apomesodon'' Poyato-Ariza & Wenz, 2002 *** Genus '' Athrodon'' Sauvage, 1880 *** Genus '' Brauccipycnodus'' Taverne & Capasso, 2021 *** Genus '' Coelodus'' Heckel, 1854 *** Genus '' Costapycnodus'' Taverne, Capasso & del Re, 2019 *** Genus '' Flagellipinna'' Cawley & Kriwet, 2019 *** Genus '' Gregoriopycnodus'' Taverne, Capasso & del Re, 2020 *** Genus '' Haqelpycnodus'' Taverne & Capasso, 2018 *** Genus '' Iemanja'' Wenz, 1989 *** Genus '' Libanopycnodus'' Taverne & Capasso, 2018 *** Genus '' Macromesodon'' Blake 1905 non Lehman, 1966 '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 ''Micropycnodon'' Hibbard & Graffham, 1945 *** Genus ?''Neomesturus'' Cooper & Martill 2020 *** Genus ''Neoproscinetes'' De Figueiredo & Silva Santos, 1990 *** Genus '' Njoerdichthys'' Cawley, Lehmann, Wiese & Kriwet, 2020 *** Genus '' Nonaphalagodus'' Thurmond, 1974 *** Genus '' Nursallia'' Blot, 1987 *** Genus '' Ocloedus'' Poyato-Ariza & Wenz, 2002 *** Genus '' Omphalodus'' von Meyer, 1847 *** 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 '' Polypsephis'' Hay, 1899 (='' Microdon'' Agassiz 1833 (preoccupied)) *** Genus ''

Potiguara The Potiguara (also Potyguara or Pitiguara) are an indigenous peoples in Brazil, indigenous people of Brazil. The Potiguara people live in Paraíba, in the municipalities of Marcação, Baía da Traição and Rio Tinto, Paraíba, Rio Tinto. Th ...

'' Machado & Brito, 2006 *** Genus '' Proscinetes'' Gistl, 1848 Microdon'' Agassiz, 1833 non Meigen, 1803 non Fritsch, 1876 non Conrad, 1842 non Gistl, 1848 non Dixon, 1850; '' Polypsephis'' Hay, 1899] *** Genus ''Pycnodus'' Agassiz, 1833 *** Genus ''Pycnomicrodon'' Hay 1916 non Hibbard & Graffham, 1941 *** Genus ''Rhinopycnodus'' Taverne & Capasso, 2013 *** Genus '' Scalacurvichthys'' Cawley & Kriwet, 2017 *** Genus '' Sigmapycnodus'' Taverne & Capasso, 2018 *** 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">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 '' Tepexichthys'' Applegate, 1992 *** Genus '' Tergestinia'' Capasso, 2000 *** Genus '' Texasensis'' Özdikmen, 2009 (='' Callodus'' Thurmond, 1974 (preoccupied)) *** Genus '' Thiollierepycnodus'' Ebert, 2020 *** Genus '' Tibetodus'' Young & Liu, 1954 *** Genus '' Turbomesodon'' Poyato-Ariza & Wenz, 2004 Macromesodon'' Lehman, 1966 non Blake, 1905">' Macromesodon'' Lehman, 1966 non Blake, 1905*** Genus '' Typodus'' Quenstedt, 1858 **Family Serrasalmimidae Vullo ''et al'', 2017 ***Genus '' Eoserrasalmimus'' Vullo ''et al'', 2017 ***Genus '' Damergouia'' Vullo ''et al'', 2017 ***Genus '' Polygyrodus'' White, 1927 ***Genus '' Serrasalmimus'' Vullo ''et al'', 2017 **Superfamily Coccodontoidea Taverne & Capasso, 2013 ***Genus '' Congopycnodus'' Taverne, 2019 ***Family Stanhopellidae Capasso, 2023 **** Genus '' Stanhopella'' Capasso, 2023 ***Family Coccodontidae Berg, 1940 **** Genus '' Coccodus'' Pictet, 1850 **** Genus '' Corusichthys'' Taverne & Capasso, 2014 **** Genus ?'' Cosmodus'' le Sauvage, 1879 '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 ''Hensodon'' Kriwet, 2004 **** Genus '' Ichthyoceros'' Gayet, 1984 **** Genus '' Paracoccodus'' Taverne & Capasso, 2014 **** Genus '' Trewavasia'' White & Moy-Thomas, 1941 'Xenopholis'' Davis, 1887 non Peters, 1869; ''Xenopholoides">Xenopholis.html" ;"title="'Xenopholis">'Xenopholis'' Davis, 1887 non Peters, 1869; ''Xenopholoides'' Fowler, 1958] ***Family Gebrayelichthyidae Nursall & Capasso, 2004 **** Genus '' Gebrayelichthys'' Nursall & Capasso, 2004 **** Genus '' Maraldichthys'' Taverne & Capasso, 2014 ***Family Gladiopycnodontidae Taverne & Capasso, 2013 **** Genus '' Ducrotayichthys'' Taverne & Capasso, 2015 **** Genus '' Gladiopycnodus'' Taverne & Capasso, 2013 **** Genus '' Hayolperichthys'' Taverne & Capasso, 2015 **** Genus '' Joinvillichthys'' Taverne & Capasso, 2014 **** Genus '' Monocerichthys'' Taverne & Capasso, 2013 **** Genus '' Pankowskichthys'' Taverne & Capasso, 2014 **** Genus '' Rostropycnodus'' Taverne & Capasso, 2013 **** Genus '' Stenoprotome'' Hay, 1903 **** Genus '' Tricerichthys'' Taverne & Capasso, 2015

Phylogeny

The phylogenetic relation between pycnodonts and other actinopterygians is uncertain. The difficulty of placing them on a phylogenetic tree arises from the fact that they are a clade defined by a high number of autapomorphies (characteristics shared by a single taxon), which makes them easy to identify, but also makes the study of their relations with other actinopterygians difficult, since characteristics shared by other groups might be obfuscated by the immense amount of features and diversity of pycnodonts. Previously, Pycnodontiformes where proposed to be a sister group of

Teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...

ei or Teleosteomorpha, but in a 2015 analysis by Poyato-Ariza, they turned up as the most basal Neopterygii among the others of the group included, those being Lepisosteiformes, Semionotiformes, Macrosemiiformes, Halecomorphi and

ei. As a means to avoid potential competition, the families of Pycnodontiforms evolved different body and jaw shapes, resulting in a highly diverse group.

were the most advanced group, being the largest family, comprising 26 known described genera.

References

* Capasso, Luigi (2021). "Pycnodonts: An overview and new insights in the Pycnodontomorpha Nursall, 2010". Occasional Paper of the University Museum of Chieti, Monographic Publication, 1: 1–223. Capasso, Luigi (2023). "Atlas of Pycnodonts: A pictorial guide to the Pycnodontomorpha (Pisces, Actinopterygii)". èDicola Publisher, Castellana, Italy; pp. 1-240. * {{Taxonbar, from=Q1787823 Prehistoric ray-finned fish orders