Belongs within: Holostei.
The Semionotiformes are a group of fishes including the modern gars and their fossil relatives, united by the absence of the intercalar and gular bones, the presence of a series of antorbitals anterior to the circum-orbital ring, and enlarged basal and fringing fulcra (Cavin 2010).
<==Semionotiformes [Ginglymodi, Semionotoidei]
| i. s.: Clastes Cope 1872C77
| |--C. aganus Cope 1877C77
| |--C. anaxC77
| |--C. atrox [=Lepidosteus atrox]C77
| |--C. cycliferusC77
| |--C. integer Cope 1877C77
| |--C. notabilis [=Lepidosteus notabilis]C77
| `--‘Lepidosteus’ simplexC77
| PneumatosteusC77
|--+--Notagogus ferreriC10, S02
| |--PropterusGX17
| | |--P. elongatusGX17
| | `--P. vidaliS02
| `--MacrosemiidaeG93
| |--Macrosemius rostratusGX17, FS10
| |--Legonotus Egerton 1854G93
| `--Enchelyolepis Woodward 1918G93
`--+--Macrosemimimus lennieriGX17
|--Sangiorgichthys aldaeC10
`--SemionotidaeC10
| i. s.: Lepidotyle Meunier & Gayet 1992GM01
| `--L. enigmatica Meunier & Gayet 1992GM01
| Alleiolepis Heller 1953G93
| Aphelolepis Heller 1953G93
| Asialepidotus Su 1959G93
| Sinosemionotus Yuan & Koh 1936G93
| Allelepidotus Frič 1906G93
| Pericentrophorus Jörg 1969G93
|--+--Semionotus Agassiz 1832C10, G93
| | |--S. bergeriC10
| | `--+--S. elegansC10
| | `--S. kanabensisC10
| `--Lepidotes Agassiz 1832C10, G93
| |--+--L. lennieriC10
| | `--+--L. gloriaeC10
| | `--L. tendaguruensisC10
| `--+----L. minorC10
| `--+--L. mantelliC10
| `--+--L. semiserratusC10
| |--+--L. elvensisC10
| | `--+--L. latifronsC10
| | `--Isanichthys palustrisC10
| `--+--L. piauhyensisC10
| `--Paralepidotus Stolley 1920C10, G93
| `--P. ornatusC10
`--+--Neosemionotus puntanusC10
`--+--‘Lepidotes’ microrhisC10
`--+--‘Lepidotes’ buddhabutrensisC10
`--+--+--Araripelepidotes temnurusC10
| `--Pliodetes nigeriensisC10
`--+--Masillosteus kelleriC10
`--Lepisosteidae [Lepisosteiformes, Lepisostoidei]B-RB13
| i. s.: Paralepidosteus Arambourg & Joleaud 1943G93
|--Obaichthys decoratusGX17
`--+--Oniichthys falipouiC10
|--Lepisosteus Lacépède 1903GX17, G93
| |--L. osseusGM01
| `--L. platostomusFS10
`--AtractosteusGX17
|--A. feroxC77
|--A. spatulaB96
|--A. tristoechusR88 [=Lepisosteus tristoechusG88]
`--A. tropicusR88
*Type species of generic name indicated
References
[B-RB13] Betancur-R., R., R. E. Broughton, E. O. Wiley, K. Carpenter, A. López, C. Li, N. I. Holcroft, D. Arcila, M. Sanciangco, J. C. Cureton, II, F. Zhang, T. Buser, M. A. Campbell, J. A. Ballesteros, A. Roa-Varon, S. Willis, W. C. Borden, T. Rowley, P. C. Reneau, D. J. Hough, G. Lu, T. Grande, G. Arratia & G. Ortí. 2013. The tree of life and a new classification of bony fishes. PLoS Currents Tree of Life April 18 2013. doi: 10.1371/currents.tol.53ba26640df0ccaee75bb165c8c26288.
[B96] Bond, C. E. 1996. Biology of Fishes 2nd ed. Saunders College Publishing: Fort Worth.
[C10] Cavin, L. 2010. Diversity of Mesozoic semionotiform fishes and the origin of gars (Lepisosteidae). Naturwissenschaften 97: 1035–1040.
[C77] Cope, E. D. 1877. Report upon the extinct Vertebrata obtained in New Mexico by parties of the expedition of 1874. Geographical Surveys West of the One Hundredth Meridian 4 (2): i–iv, 1–370.
[FS10] Friedman, M., K. Shimada, L. D. Martin, M. J. Everhart, J. Liston, A. Maltese & M. Triebold. 2010. 100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas. Science 327: 990–993.
[G93] Gardiner, B. G. 1993. Osteichthyes: basal actinopterygians. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 611–619. Chapman & Hall: London.
[GM01] Gayet, M., L. G. Marshall, T. Sempere, F. J. Meunier, H. Cappetta & J-C. Rage. 2001. Middle Maastrichtian vertebrates (fishes, amphibians, dinosaurs and other reptiles, mammals) from Pajcha Pata (Bolivia). Biostratigraphic, palaeoecologic and palaeobiostratigraphic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 169: 39–68.
[GX17] Giles, S., G.-H. Xu, T. J. Near & M. Friedman. 2017. Early members of ‘living fossil’ lineage imply later origin of modern ray-finned fishes. Nature 549: 265–268.
[G88] Gray, J. 1988. Evolution of the freshwater ecosystem: the fossil record. Palaeogeography, Palaeoclimatology, Palaeoecology 62: 1–214.
[R88] Rauchenberger, M. 1988. Historical biogeography of poeciliid fishes in the Caribbean. Systematic Zoology 37 (4): 356–365.
[S02] Sinitshenkova, N. D. 2002. Ecological history of the aquatic insects. In: Rasnitsyn, A. P., & D. L. J. Quicke (eds) History of Insects pp. 388–426. Kluwer Academic Publishers: Dordrecht.