Eugeneodontida Explained

The Eugeneodontida, sometimes also called Eugeneodontiformes, is an extinct and poorly known order of cartilaginous fishes. They possessed "tooth-whorls" on the symphysis of either the lower or both jaws and pectoral fins supported by long radials. They probably lacked pelvic fins and anal fins.^[1] The palatoquadrate was either fused to the skull or reduced. Now determined to be within the Holocephali, their closest living relatives are chimaeras. The eugeneodonts are named after paleontologist Eugene S. Richardson, Jr.^[2] The group first appeared in the fossil record during the late Mississippian (Serpukhovian).^[3] The youngest eugeneodonts are known from the Early Triassic.^[4] The geologically youngest fossils of the group are known from the Sulphur Mountain Formation (western Canada), Vardebukta Formation (Svalbard, Norway) and Wordie Creek Formation (Greenland).

Members of the Eugeneodontida are further classified into different families, the most well-preserved members that have been discovered are commonly placed within the families Helicoprionidae ("spiral saws"), and Edestidae ("those which devour"), the former containing the genera Helicoprion, Sarcoprion, and Parahelicoprion, and the latter containing the genera Edestus, Lestrodus, and Metaxyacanthus. All eugeneodonts are thought to have been obligate carnivores, with each genus having specialized feeding behaviors, territory ranges, and specific prey.

Among the eugeneodonts, some members of the superfamily Edestoidea are probably the largest marine animals of their time, with the Late Carboniferous Edestus estimated to reach about or exceeding 6.7m (22feet) in length,^{[5] [6]} with some Early Permian Helicoprion suggested to be over 7.6m (24.9feet) long by some estimates^[7] (though the body length estimates for both genera are somewhat speculative due to both only being known from skull material).

Taxonomy

The list below shows taxa included within Eugeneodontida.^[8]

• Superfamily Caseodontoidea
  • Family Caseodontidae
    • Genus Caseodus
    • Genus Erikodus
    • Genus Fadenia
    • Genus Ornithoprion
    • Genus Pirodus
    • Genus Romerodus
  • Family Eugeneodontidae
    • Genus Bobbodus
    • Genus Eugeneodus
    • Genus Gilliodus
  • Family incertae sedis
    • Genus Campodus
    • Genus Chiastodus
    • Genus Tiaraju
• Superfamily Edestoidea
  • Family Helicoprionidae
    • Genus Agassizodus
    • Genus Arpagodus
    • Genus Campyloprion
    • Genus Helicoprion
    • Genus Parahelicoprion
    • Genus Sarcoprion
    • Genus Sinohelicoprion
    • Genus Toxoprion
  • Family Edestidae
    • Genus Edestus
    • Genus Helicampodus
    • Genus Lestrodus
    • Genus Parahelicampodus
    • Genus Syntomodus
    • Genus Protopirata
    • Genus Euctenius
    • Genus Prospiraxis
    • Genus Spiraxis
    • Genus Metaxyacanthus
  • Family incertae sedis
    • Genus Paredestus

External links

• http://palaeos.com/vertebrates/chondrichthyes/chondrichthyes.html#Eugeneodontida Palaeos Vertebrates 70.100 Chondrichthyes: Eugnathostomata at paleos.com
• JSTOR: Journal of Paleontology Vol. 70, No. 1 (Jan., 1996), pp. 162-165
• More about Chondrichthyes at Devonian Times

Notes and References

1. Lebedev. O.A.. 2009. A new specimen of Helicoprion Karpinsky, 1899 from Kazakhstanian Cisurals and a new reconstruction of its tooth whorl position and function. Acta Zoologica. 90. 171–182. 10.1111/j.1463-6395.2008.00353.x. 0001-7272.
2. Book: Zangerl, R. . 1981 . Handbook of Paleoichthyology. Volume 3A. Chondrichthyes I. Paleozoic Elasmobranchi . Stuttgart . Gustav Fischer Verlag . 978-3-89937-045-4.
3. Hodnett . John-Paul M. . Elliott . David K. . December 2018 . Carboniferous chondrichthyan assemblages from the Surprise Canyon and Watahomigi formations (latest Mississippian–Early Pennsylvanian) of the western Grand Canyon, Northern Arizona . Journal of Paleontology . en . 92 . S77 . 1–33 . 10.1017/jpa.2018.72 . 0022-3360. free .
4. Scheyer . Torsten M. . Romano . Carlo . Jenks . Jim . Bucher . Hugo . Early Triassic Marine Biotic Recovery: The Predators' Perspective . PLOS ONE . 19 March 2014 . 9 . 3 . e88987 . 10.1371/journal.pone.0088987 . 24647136 . 3960099 . 2014PLoSO...988987S . free .
5. Tapanila. Leif. Pruitt. Jesse. 2019-09-04. Redefining species concepts for the Pennsylvanian scissor tooth shark, Edestus. PLOS ONE. en. 14. 9. e0220958. 10.1371/journal.pone.0220958. 1932-6203. 6726245. 31483800. 2019PLoSO..1420958T. free.
6. Engelman . Russell K. . 2023 . A Devonian Fish Tale: A New Method of Body Length Estimation Suggests Much Smaller Sizes for Dunkleosteus terrelli (Placodermi: Arthrodira) . Diversity . en . 15 . 3 . 318 . 10.3390/d15030318 . 1424-2818 . free .
7. Tapanila . Leif . Pruitt . Jesse . Wilga . Cheryl D. . Pradel . Alan . 2020 . Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition . The Anatomical Record . en . 303 . 2 . 363–376 . 10.1002/ar.24046 . 1932-8494 . 30536888 . free.
8. Book: Ginter . M. . Hampe . O. . Duffin . C. . 2010 . Handbook of Paleoichthyology. Volume 3D. Chondrichthyes. Paleozoic Elasmobranchi: Teeth . Munich . Verlag Dr. Friedrich Pfeil . 978-3-89937-116-1.