Pachycormiformes

Pachycormiformes is an extinct order of marine ray-finned fish known from the Early Jurassic to the end of the Cretaceous. It only includes a single family, Pachycormidae. They were characterized by having serrated pectoral fins (though more recent studies demonstrated that fin shape diversity in this group was high[2]), reduced pelvic fins and a bony rostrum. Their exact relations with other fish are unclear, but they are generally considered to be teleosteomorphs, more closely related to teleosts than to Holostei. Pachycormiformes are morphologically diverse, containing both tuna and swordfish-like carnivorous forms, as well as edentulous suspension-feeding forms, with the latter including the largest ray-finned fish known to have existed, Leedsichthys, with an estimated maximum length of 16 metres.

Pachycormiformes
Temporal range: Early Jurassic - Late Cretaceous,
Skeleton of Pachycormus
Skeleton of Orthocormus
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: †Pachycormiformes
Berg 1937
Family: †Pachycormidae
Woodward, 1895
Type genus
Pachycormus
Agassiz, 1833
Genera

See text

Synonyms[1]
  • Diphyodontidae Jordan, 1923
  • Erisichtheidae Cope, 1877b
  • Microlepidoti Zittel, 1887
  • Pelecopteridae Cope, 1875
  • Protosphyraenidae Lydekker, 1889
  • Sauropsidae Cope, 1877a
  • Saurotomini [Saurostomini] Bonaparte, 1846 corrig. Bonaparte 1850a

Synapomorphies
Size comparison of various species of Pachycormiform fish

Pachycormiformes are united by "a compound bone (rostrodermethmoid) forming the anterodorsal border of the mouth; a reduced coronoid process of the mandible; absence of supraorbitals associated with a dermosphenotic defining the dorsal margin of the orbit; two large, plate-like suborbital bones posterior to the infraorbitals; long, slender pectoral fins; asymmetrical branching of pectoral fin lepidotrichia; considerable overlap of the hypurals by caudal fin rays (hypurostegy); and the presence of distinctive uroneural-like ossifications of the caudal fin endoskeleton".[3]

Relationships

Pachycormiformes are generally interpreted as members of Teleosteomorpha, the group that includes all fish more closely related to modern teleosts than to Holostei (the group containing bowfin and gars), often they have been considered to be the sister group of the Aspidorhynchiformes.[4]

Taxonomy

Taxonomy according to Cooper et al. (2022):[5]

Cladistics according to Friedman et al. (2010).[7]

Pachycormiformes

†Euthynotus

†Hypsocormus insignis

†"Hypsocormus" tenuirostris

†Orthocormus

†Australopachycormus

†Protosphyraena

†Pachycormus

Suspension feeding clade

†Asthenocormus titanius

†Martillichthys renwickae

†Bonnerichthys gladius

†Leedsichthys problematicus

†Rhinconichthys taylori

References
  1. van der Laan, R. (2018). "Family-group names of fossil fishes". European Journal of Taxonomy (466). doi:10.5852/ejt.2018.466.
  2. Liston, Jeff J.; Maltese, Anthony E.; Lambers, Paul H.; Delsate, Dominique; Harcourt-Smith, William E. H.; Heteren, Anneke H. van (2019-11-07). "Scythes, sickles and other blades: defining the diversity of pectoral fin morphotypes in Pachycormiformes". PeerJ. 7: e7675. doi:10.7717/peerj.7675. ISSN 2167-8359. PMC 6842561. PMID 31720097.
  3. Dobson, Claire; Giles, Sam; Johanson, Zerina; Liston, Jeff; Friedman, Matt (2019-09-03). "Cranial osteology of the Middle Jurassic (Callovian) Martillichthys renwickae (Neopterygii, Pachycormiformes) with comments on the evolution and ecology of edentulous pachycormiforms". Papers in Palaeontology. 7: 111–136. doi:10.1002/spp2.1276. hdl:2027.42/167090. ISSN 2056-2802. S2CID 202919395.
  4. Peskin, Brianna; Henke, Katrin; Cumplido, Nicolás; Treaster, Stephen; Harris, Matthew P.; Bagnat, Michel; Arratia, Gloria (2020-07-20). "Notochordal Signals Establish Phylogenetic Identity of the Teleost Spine". Current Biology. 30 (14): 2805–2814.e3. doi:10.1016/j.cub.2020.05.037. ISSN 0960-9822. PMC 8159021. PMID 32559448.
  5. Cooper, S. L. A.; Giles, S.; Young, H.; Maxwell, E. E. (2022). "A New Large †Pachycormiform (Teleosteomorpha: †Pachycormiformes) from the Lower Jurassic of Germany, with Affinities to the Suspension-Feeding Clade, and Comments on the Gastrointestinal Anatomy of Pachycormid Fishes". Diversity. 14 (12): 1026. doi:10.3390/d14121026.
  6. Gouiric-Cavalli, S.; Arratia, G. (2022). "A new †Pachycormiformes (Actinopterygii) from the Upper Jurassic of Gondwana sheds light on the evolutionary history of the group". Journal of Systematic Palaeontology. 19 (21): 1517–1550. doi:10.1080/14772019.2022.2049382. S2CID 248454343.
  7. Matt Friedman; Kenshu Shimada; Larry D. Martin; Michael J. Everhart; Jeff Liston; Anthony Maltese; Michael Triebold (2010). "100-million-year dynasty of giant planktivorous bony fishes in the Mesozoic seas". Science. 327 (5968): 990–993. Bibcode:2010Sci...327..990F. doi:10.1126/science.1184743. PMID 20167784. S2CID 206524637.
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