Ichthyodectiformes is an extinct order of marine stem-teleost ray-finned fish. The order is named after the genus Ichthyodectes, established by Edward Drinker Cope in 1870. Ichthyodectiforms are usually considered to be some of the closest relatives of the teleost crown group.
They were most diverse throughout the Cretaceous period, though basal forms like Thrissops, Occithrissops and Allothrissops are known from the Middle-Late Jurassic of Europe and North America. They were almost entirely wiped out by the Cretaceous-Paleogene extinction event, but a single species, Saurocephalus lanciformis, appears to have survived into the earliest Paleocene (Danian).
Most ichthyodectiforms ranged between in length. Most of known taxa were predators, feeding on smaller fish; in several cases, larger ichthyodectiforms preyed on smaller members of the order. Some species had remarkably large teeth, though others, such as Gillicus arcuatus, had small ones and sucked in their prey. Heckelichthys preopercularis is a rare example of non-predatory ichthyodectiform, more likely to be microphagous, fed on small particles. There is evidence that at least one species, Xiphactinus audax, may have been endothermic ("warm-blooded"). Another genus, Dugaldia, may have been able to laterally open its mouth extremely wide in a manner akin to the modern sarcastic fringehead.
Systematics The basal phylogeny is badly resolved, leading to many ichthyodectiforms that are simply known to be rather primitive, but where nothing certain can be said about their precise relationships.
Ichthyodectiformes Africathrissops Taverne, 2010 Allothrissops Nybelin, 1964 Antarctithrissops Arratia et al., 2004 Ascalabothrissops? Arratia, 2000 Capassoichthys Taverne, 2015 Carsothrissops d'Erasmo, 1946 Dugaldia Lees, 1990 Faugichthys Taverne & Chanet, 2000 Furloichthys Taverne & Capasso, 2018 Occithrissops Schaeffer & Patterson, 1984 Ogunichthys Alvarado-Ortega & Brito, 2009 Pachythrissops? Woodward, 1919 Prymnetes Cope, 1871 Thrissops Agassiz, 1843 Sultanuvaisia Nesov, 1981 Unamichthys Alvarado-Ortega, 2004 Verraesichthys Taverne, 2010 Chuhsiungichthyidae? Yabumoto, 1994 Chuhsiungichthys? Lew, 1974 Jinjuichthys? Kim et al., 2014 Mesoclupea? Ping & Yen, 1933 Bardackichthyidae? Hacker & Shimada, 2021 Bardackichthys? Hacker & Shimada, 2021 Cladocyclidae Maisey, 1991 Aidachar Nesov, 1981 Chirocentrites Heckel, 1849 Chiromystus Cope, 1885 Cladocyclus Agassiz, 1841 Cladocynodon de Mayrinck et al., 2023 Eubiodectes Hay, 1903 Ichthyodectidae Crook, 1892 Cooyoo Bartholomai & Less, 1987 Ghrisichthys Cavin et al., 2013 Ichthyodectes Cope, 1870 Postredectes Kaddumi, 2009 Xiphactinus Leidy, 1870 Heckelichthyidae Alvarado-Ortega, 2024 Altamuraichthys? Taverne, 2016 Amakusaichthys Yabumoto et al., 2020 Garganoichthys? Taverne, 2009 Heckelichthys Taverne, 2008 Saurodontidae Cope, 1870Cope, E. D. (1870). On the Saurodontidæ. Proceedings of the American Philosophical Society 11:529-538Cope, E. D. (1873). On two new species of Saurodontidae. Proceedings of the Academy of Natural Sciences of Philadelphia 25:2-339 Gillicus Cope, 1875 Gwawinapterus Arbour & Currie, 2011Vullo, R., Buffetaut, E. and Everhart, M.J. (2012). "Reappraisal of Gwawinapterus beardi from the Late Cretaceous of Canada: a saurodontid fish, not a pterosaur." Journal of Vertebrate Paleontology, 32(5): 1198-1201. Prosaurodon Stewart, 1999 Saurocephalus Harlan, 1824 Saurodon Hay, 1830 Vallecillichthys Blanco & Cavin, 2003 Wadiichthys Abu El-Kheir, 2026
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