Semionotiformes is an order of ray-finned fish known from the Middle Triassic (Anisian) to the Late Cretaceous (Maastrichtian). It is the sister group to Lepisosteiformes, the order containing fish such as Lepidotes and Gars. The group includes both freshwater (Semionotidae) and marine (Callipurbeckiidae, Macrosemiidae) adapted forms. Many members of the family Macrosemiidae, had elongated dorsal fins, often associated with an adjacent area of skin which was free of scales. These fins were likely undulated for use in precision swimming. The body morphology of macrosemiids suggests that they were slow swimmers who were capable of maneuvering around complex topography, such as reef environments.
Classification Order †Semionotiformes Arambourg & Bertin 1958 sensu López-Arbarello 2012 Genus ?†Orthurus Kner 1866 Genus ?†Aphanepygus Bassani 1879 Genus †Alleiolepis Heller 1953 Genus †Aphelolepis Heller 1953 Genus †Austrolepidotes Bocchino, 1974 Genus †Corunegenys Wade, 1942 Genus †Pericentrophorus Jorg 1969 Genus †Prionopleurus Fischer de Waldheim 1852 Genus †Quasimodichthys Paiva and Gallo 2018 Genus †Sinosemionotus Yuan and Koh 1936 Genus †Uarbryichthys Wade 1941 Family †Macrosemiidae Wagner 1860a corrig. Cope 1889 sensu Murray & Wilson 2009 [Macrosemii Wagner 1860a] Genus †Enchelyolepis Woodward 1918 Genus †Palaeomacrosemius Ebert, Lane & Kolbl-Ebert 2016 Genus †Voelklichthys Arratia & Schultze 2012 Genus †Notagogus Agassiz 1833-1844 [Neonotagogus Bravi 1994] Genus †Agoultichthys Murray & Wilson 2009 Genus †Histionotus Egerton 1854 Genus †Propterus Agassiz 1833-1844 [Rhynchoncodes Costa 1850] Genus †Macrosemiocotzus González-Rodríguez, Applegate & Espinosa-Arrubarrena 2004 Genus †Legnonotus Egerton 1853 Genus †Macrosemius Agassiz 1833-1844 Family †Semionotidae Woodward 1890 sensu López-Arbarello 2012 Genus †Semionotus Agassiz 1832 (Usually considered a wastebasket taxon) Genus †Lophionotus Gibson 2013 Family †Callipurbeckiidae López-Arbarello 2012 [Paralepidotidae Hadding 1919 ex Lund 1920] Genus †Occitanichthys López-Arbarello & Wencker 2016 Genus †Semiolepis Lombardo & Tintori 2008 Genus †Paralepidotus Stolley 1919 Genus †Macrosemimimus Schröder, López-Arbarello & Ebert 2012 Genus †Tlayuamichin López-Arbarello & Alvarado-Ortega 2011 Genus †Callipurbeckia López-Arbarello 2012
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