Redfieldiiformes is an extinct order of ray-finned fish (actinopterygians) which lived from the Early Triassic to Early Jurassic. Redfieldiiforms were fairly typical Triassic fish in overall anatomy. They had a fusiform (streamlined, tuna-like) body shape with thick, ganoine-covered scales. The dorsal and anal fins were large, positioned opposite from each other, and shifted back, close to the tail. The caudal fin was hemiheterocercal, with the vertebral column and body scales extending into an upper lobe equal in size and shape to the lower lobe. They also had several characteristic skeletal traits, such as a hatchet-shaped preopercle, a series of fulcra (thin spiny scales) fringing the fins, a reduced number of branchiostegal rays (typically just one), and a snout ornamented with tubercles.[1][2][3]
| Redfieldiiformes Temporal range:
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| Dictyopyge macrurus from the Late Triassic of Virginia | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Subclass: | Neopterygii (?) |
| Order: | †Redfieldiiformes Berg, 1940 |
| Type genus | |
| †Redfieldius Hay, 1899
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| Genera | |
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See text | |
The maxilla has small teeth and is strongly connected to the preopercle; this would have allowed a deep gape to assist in ram feeding.[1] The function of the snout tubercles is uncertain; some authors have suggested that they attached to a fleshy upper lip,[2] while others argue that they could have held sensory organs akin to the tubercles of siluriforms (catfish).[3]
Redfieldiiforms were fairly primitive 'subholostean' fish (more primitive than holosteans such as gars or the bowfin), with uncertain relations to neopterygians.[1] Some studies draw comparisons to 'perleidiforms' or ptycholepids, while others consider redfieldiiforms to be early neopterygians related to pholidopleuriforms.[4] Redfieldiiforms were exclusively freshwater fish which became prominent in southern Gondwana (Argentina, Australia, southern Africa) during the Middle Triassic.[3] By the Late Triassic they had become a major component of freshwater ecosystems in western Laurasia (North America and Morocco). However, they were much rarer further east (South Korea,[3] possibly Switzerland[5]). The last member of the order, Redfieldius, lived in the Early Jurassic of eastern North America.[1][3]
Taxonomy
editThe following families and genera are known:
- Order Redfieldiiformes
- Genus Calaichthys[1]
- Genus Denwoodichthys?
- Genus Endemichthys?
- Genus Helichthys
- Genus Hiascoactinus[3]
- Genus Sakamenichthys?
- Genus Sinkiangichthys (nomen dubium)?
- Family Brookvaliidae
- Genus Atopocephala
- Genus Brookvalia
- Genus Ischnolepis
- Genus ?Leighiscus
- Genus Phlyctaenichthys
- Genus Schizurichthys (formerly placed in the family Schizurichthyidae)
- Family Redfieldiidae
- Genus Cionichthys
- Genus Daedalichthys
- Genus Dictyopyge
- Genus Geitonichthys
- Genus Lasalichthys (=Synorichthys)[6]
- Genus Mauritanichthys
- Genus Molybdichthys
- Genus Redfieldius
The enigmatic marine fish Pacorichthys from the Ladinian of Europe somewhat resembles a redfieldiiform, although it was marine unlike the freshwater nature of other redfieldiiforms.[5]
References
edit- ^ a b c d e Gouiric-Cavalli, Soledad; Zavattieri, Ana M.; Gutierrez, Pedro R.; Cariglino, Bárbara; Balarino, Lucía (2017). "Increasing the fish diversity of the Triassic faunas of Gondwana: a new redfieldiiform (Actinopterygii) from the Middle Triassic of Argentina and its palaeobiogeographical implications". Papers in Palaeontology. 3 (4): 559–581. doi:10.1002/spp2.1089. hdl:11336/57303. ISSN 2056-2802. S2CID 134580710.
- ^ a b Gibson, Sarah Z. (2018-09-03). "A new species of Lasalichthys (Actinopterygii, Redfieldiiformes) from the Upper Triassic Dockum Group of Howard County, Texas, with revisions to the genera Lasalichthys and Synorichthys". Journal of Vertebrate Paleontology. 38 (5): e1513009. Bibcode:2018JVPal..38E3009G. doi:10.1080/02724634.2018.1513009. ISSN 0272-4634. S2CID 92328870.
- ^ a b c d e f Kim, Su-Hwan; Lee, Yuong-Nam; Park, Jin-Young; Lee, Sungjin; Lee, Hang-Jae (2020-04-01). "The first record of redfieldiiform fish (Actinopterygii) from the Upper Triassic of Korea: Implications for paleobiology and paleobiogeography of Redfieldiiformes". Gondwana Research. 80: 275–284. Bibcode:2020GondR..80..275K. doi:10.1016/j.gr.2019.11.008. ISSN 1342-937X. S2CID 213571269.
- ^ Xu, Guang-Hui (2021). "A new stem-neopterygian fish from the Middle Triassic (Anisian) of Yunnan, China, with a reassessment of the relationships of early neopterygian clades". Zoological Journal of the Linnean Society. 191 (2): 375–394. doi:10.1093/zoolinnean/zlaa053.
- ^ a b Lombardo, Cristina (2013). "A new basal actinopterygian fish from the Late Ladinian of Monte San Giorgio (Canton Ticino, Switzerland)". Swiss Journal of Geosciences. 106 (2): 219–230. doi:10.1007/s00015-013-0125-9. ISSN 1661-8734. S2CID 129121812.
- ^ Gibson, Sarah Z. (2018-09-03). "A new species of Lasalichthys (Actinopterygii, Redfieldiiformes) from the Upper Triassic Dockum Group of Howard County, Texas, with revisions to the genera Lasalichthys and Synorichthys". Journal of Vertebrate Paleontology. 38 (5): e1513009. doi:10.1080/02724634.2018.1513009. ISSN 0272-4634.
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