Palaeonisciformes

Platysomus, from here.

Belongs within: Actinopteri.

The Palaeonisciformes are an early group of heavily scaled ray-finned fishes known from the Devonian to the Cretaceous (Bond 1996).

Shadow of the palaeoniscoids
Published 27 November 2021
Palaeoniscum freieslebeni, copyright James St. John.

Depending how you cut it, the ray-finned fishes (Actinopterygii) are arguably the most diverse group of vertebrates in the modern fauna. They are the dominant vertebrates in all aquatic environments, they encompass an enormous array of species, and they have evolved a bewildering assemblage of morphologies. But despite their current pre-eminence, the early evolution of actinopterygians remains rather understudied. The earliest actinopterygians appear in the fossil record in the Late Silurian/Early Devonian but, until fairly recently, the majority of Palaeozoic ray-finned fishes have often been lumped into a catch-all holding tank, the ‘Palaeonisciformes’. This was a vague assemblage of fishes united by plesiomorphic features such as ganoid scales (heavy, bony scales with an outer layer of enamel, also found in modern gars and sturgeons), a single dorsal fin and a heterocercal tail (with the upper arm of the tail fin longer than the lower). The key genus of the group, the Permian Palaeoniscum, had a fusiform (or torpedo-shaped) body; at first glance, it would not have looked dissimilar to a modern herring. However, it lacked the mobile jaw structure of modern teleost fishes, with the maxilla and preopercular bones being fixed together. As such, it would have lacked the modern fish’s capacity for suction feeding (Lauder 1980). Prey capture by Palaeoniscum would have been a simple smash-and-grab affair. Palaeoniscoid fishes remained a component of both marine and freshwater faunas until the end of the Cretaceous before being entirely supplanted by modern teleost radiations such as the ostariophysans and percomorphs.

Reconstruction of Acrolepis gigas, copyright DiBgd.

The core concept of ‘Palaeonisciformes’ has united fishes with a fusiform body shape like Palaeoniscum; depending on the author, more divergent contemporary fishes such as the deep-body platysomoids might be combined in the same order or treated separately. By modern standards, former ‘Palaeonisciformes’ probably combine stem-actinopterygians, stem-chondrosteans, stem-holosteans and possibly even stem-teleosts. As such, the term Palaeonisciformes has tended to fall out of favour, though the less formal ‘palaeoniscoid’ remains a useful descriptor. Nevertheless, the exact phylogenetic position of many palaeoniscoid taxa remains unestablished. Part of this is due to a lack of observable detail: though those heavy ganoid scales preserve well, they effectively cover up internal skeletal features. Many palaeoniscoids are preserved as compression fossils, effectively not much more than intriguing silhouettes. However, part of the problem is simple neglect. Palaeoniscoids are not rare fossils; in some formations, they may be the dominant part of the fauna by a large margin. They certainly deserve a closer look.

Systematics of Palaeonisciformes

Characters (from Bond 1996): Body form varying from fusiform to compressiform; usually covered by ganoid scales. Head large, bony; mouth generally long, teeth conical; maxillary large, probably not movable.

<==Palaeonisciformes [Platysomiformes]
    |--Palaeoniscidae [Palaeoniscoidei]B96
    |    |--PalaeoniscumEB99
    |    |    |--*P. freieslebeniEB99
    |    |    |--P. capensis Broom 1913EB99
    |    |    `--P. macropomusM79
    |    `--CosmolepisG93
    |         |--C. egertoni Egerton 1858G93
    |         `--C. ornatus (Egerton 1854)G93
    |--Redfieldiidae [Redfieldiiformes, Redfieldioidei]B96
    |    |--Sakamenichthys germaini Nauche 1959G93
    |    |--Atopocephalus Brough 1934G93
    |    |--Daedalichthys Brough 1930G93
    |    |--Helichthys Broom 1909G93
    |    |--Redfieldius Hay 1902G93
    |    |--Brookvalia Wade 1935G93
    |    |    `--B. gracilisF71
    |    |--Dictyopyge Egerton 1847G93
    |    |    |--D. illustrans Woodward 1890F71
    |    |    |--D. robusta Woodward 1890F71
    |    |    `--D. symmetrica Woodward 1890F71
    |    `--Phlyctaenichthys pectinatusC93
    `--PlatysomoideiB96
         |--ChirondontidaeB96
         `--PlatysomidaePL00
              |--Mesolepis Young 1866G93
              |--Paramesolepis Moy-Thomas & Dyne 1938G93
              |    `--P. tuberculataC93
              |--Wardichthys Traquair 1875G93
              |--Caruichthys ornatus Broom 1913G93
              |--Dorsolepis virgatus Jörg 1969G93
              |--KargalichthysTT05
              |    |--K. efremovi Minikh 1986TT05
              |    `--K. pritokensis Minikh 1992TT05
              |--Frederichthys Coates 1993C93
              |    `--*F. musadentatus Coates 1993C93
              `--Platysomus Agassiz 1833G93
                   |--P. bashkirus Minikh 1992TT05
                   |--P. biarmicus Von Eichwald 1861TT05
                   |--P. soloduchi Minikh 1992TT05
                   `--P. superbusPL00
Palaeonisciformes incertae sedis:
  PygopteridaeP99
    |--Watsonichthys Aldinger 1937P99, EB99
    |    |--W. lotzi (Gürich 1923) [=Acrolepis lotzi]EB99
    |    `--W. pectinatus (Traquair 1877)P99
    |--Nematoptychius Traquair 1875P99
    |    `--*N. greenocki Traquair 1875P99
    `--Progyrolepis Fritsch 1895P99
         |--*P. speciosus (Fritsch 1875)P99
         |--P. heyleri Poplin 1999P99
         `--P. tricessimalaris Dunkle 1946P99
  Centrolepis [Centrolepididae]G93
    `--C. aspera Agassiz 1844G93
  CoccolepididaeG93
    |--Plesiococcolepis humanensia Wang 1977G93
    |--Sunolepis yumenensis Liu 1957G93
    `--CoccolepisG93
         |--C. australis Woodward 1895F71
         |--C. liassica Woodward 1890G93
         `--C. macroptera Traquair 1911G93
  Asarotus Schaeffer 1968 [Asarotidae]G93

*Type species of generic name indicated

References

[B96] Bond, C. E. 1996. Biology of Fishes 2nd ed. Saunders College Publishing: Fort Worth.

[C93] Coates, M. I. 1993. New actinopterygian fish from the Namurian Manse Burn Formation of Bearsden, Scotland. Palaeontology 36: 123–146.

[EB99] Evans, F. J., & P. A. Bender. 1999. The Permian Whitehill Formation (Ecca Group) of South Africa: a preliminary review of palaeoniscoid fishes and taphonomy. Records of the Western Australian Museum Supplement 57: 175–181.

[F71] Fletcher, H. O. 1971. Catalogue of type specimens of fossils in the Australian Museum, Sydney. Australian Museum Memoir 13: 1–167.

[G93] Gardiner, B. G. 1993. Osteichthyes: basal actinopterygians. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 611–619. Chapman & Hall: London.

Lauder, G. V., Jr. 1980. Evolution of the feeding mechanism in primitive actinopterygian fishes: a functional anatomical analysis of Polypterus, Lepisosteus, and Amia. Journal of Morphology 163: 283–317.

[M79] Müller, A. H. 1979. Fossilization (taphonomy). In: Robison, R. A., & C. Teichert (eds) Treatise on Invertebrate Paleontology pt A. Introduction. Fossilisation (Taphonomy), Biogeography and Biostratigraphy pp. A2–A78. The Geological Society of America, Inc.: Boulder (Colorado), and The University of Kansas: Lawrence (Kansas).

[P99] Poplin, C. 1999. Un paléoniscoïde (Pisces, Actinopterygii) de Buxières-les-Mines, témoin des affinités fauniques entre Massif central et Bohême au passage Carbonifère-Permien. Geodiversitas 21 (2): 147–155.

[PL00] Poplin, C., & R. Lund. 2000. Two new deep-bodied palaeoniscoid actinopterygians from Bear Gulch (Montana, USA, Lower Cretaceous). Journal of Vertebrate Paleontology 20 (3): 428–449.

[TT05] Tverdokhlebov, V. P., G. I. Tverdokhlebova, A. V. Minikh, M. V. Surkov & M. J. Benton. 2005. Upper Permian vertebrates and their sedimentological context in the South Urals, Russia. Earth-Science Reviews 69: 27–77.

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