Eugeneodus

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Eugeneodus
Temporal range: Carboniferous 315–307  Ma
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order:† Eugeneodontiformes
Family:† Eugeneodontidae
Genus:† Eugeneodus
Zangerl, 1981
Species
  • †E. richardsoniZangerl, 1981

Eugeneodus is an extinct genus of eugeneodontid cartilaginous fish from the Carboniferous of North America. A single species, E. richardsoni, is known, and both its genus and species name honor paleontologist Eugene S. Richardson Jr. It is differentiated from its close relatives by the unfused nature of the neural and haemal arches in its caudal fin and the anatomy of its flattened, rectangular teeth (termed pavement teeth). It is the type genus of the order Eugeneodontiformes.

Contents

Discovery and naming

Specimens now assigned to Eugeneodus were first discovered during the late 1950s in Carboniferous-age shales in the Midwestern United States. [1] [2] These fossils were first tentatively assigned to the genus Agassizodus . [3] [4] In 1981, the genus was formally described by researcher Rainer Zangerl, along with a single species, Eugeneodus richardsoni. [1] Both the genus and species name honor paleontologist Eugene S. Richardson. [1] [5]

Description

Eugeneodus had jaws lined with flattened, rectangular teeth termed pavement teeth, which had sharp edges and a series of ridges along their edge, but were not blade-like. [1] [6] Along the midline of its Meckel's cartilages (lower jaws) was a row of teeth forming a tooth-whorl. [1] [6] The palatoquadrates (upper jaws) were not fused to the chondrocranium (braincase), but were relatively small braced tightly against it. [1] [7] The body was fusiform, and the tail fin was lunate (crescent-shaped) and homocercal. [1] No specimens of E. richardsoni preserve pelvic fins or claspers, [1] and these are thought to have been absent in life. [8] The internal skeleton of the tail fin consisted of neural and haemal arches, but unlike in other closely related fishes these were not fused together. [1] Exteriorly, the body was covered by a coating of small placoid scales termed lepidomoria. [9] [10] [11] These scales came in the form of both unfused, leaf-shaped scales and masses of fused scales all growing from the same base. [9] [11]

Classification

Eugeneodus is the type genus of the family Eugeneodontidae and the broader order Eugeneodontiformes, [1] [6] [12] which are named after the genus. [5] The superfamily which includes Eugeneodontidae has been referred to as either Caseodontoidea or Eugeneodontoidei. [1] [12] [13]

Eugeneodus was regarded as the most skeletally primitive eugeneodont by Zangerl. [1]

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 Zangerl, Rainer (1981). Chondrichthyes I: paleozoic Elasmobranchii. Handbook of paleoichthyology. Fischer. pp. 2, 74–91. ISBN   978-3-437-30337-1.
  2. ↑ Bruner, John Clay; Bruner, John Clay; History, Field Museum of Natural (1992). A catalogue of type specimens of fossil fishes in the Field Museum of Natural History. Chicago, Ill: Field Museum of Natural History. p. 28. doi:10.5962/bhl.title.3361.
  3. ↑ Zangerl, Rainer; Zangerl, Rainer (1966). A new shark of the family Edestidae, Ornithoprion hertwigi, from the Pennsylvanian Mecca and Logan quarry shales of Indiana. [Chicago]: Field Museum of Natural History. pp. 38–41. doi:10.5962/bhl.title.5302.
  4. ↑ Zangerl, Rainer (1995). "The Problem of Vast Numbers of Cladodont Shark Denticles in the Pennsylvanian Excello Shale of Pike County, Indiana". Journal of Paleontology. 69 (3): 562. ISSN   0022-3360.
  5. 1 2 Ewing, Susan (2017). Resurrecting the shark: a scientific obsession and the Mavericks who solved the mystery a 270 million year old fossil. New York London: Pegasus Books. p. 149. ISBN   978-1-68177-343-8.
  6. 1 2 3 Ginter, Michał; Hampe, Oliver; Duffin, Christopher J. (2010). Handbook of paleoichthyology: teeth. München: F. Pfeil. pp. 121–122. ISBN   978-3-89937-116-1.
  7. ↑ Mutter, Raoul J.; Neuman, Andrew G. (2008). "New eugeneodontid sharks from the Lower Triassic Sulphur Mountain Formation of Western Canada". Geological Society, London, Special Publications. 295 (1): 9–41. doi:10.1144/SP295.3. ISSN   0305-8719.
  8. ↑ Maisey, John G. (1986). "Heads and Tails: A Chordate Phylogeny" . Cladistics. 2 (4): 201–256. doi:10.1111/j.1096-0031.1986.tb00462.x. ISSN   1096-0031.
  9. 1 2 Zangerl, Rainer; Zangerl, Rainer (1966). A new shark of the family Edestidae, Ornithoprion hertwigi, from the Pennsylvanian Mecca and Logan quarry shales of Indiana. [Chicago]: Field Museum of Natural History. doi:10.5962/bhl.title.5302.
  10. ↑ Zangerl, Rainer (1995). "The problem of vast numbers of cladodont shark denticles in the Pennsylvanian Excello Shale of Pike County, Indiana" . Journal of Paleontology. 69 (3): 556–563. doi:10.1017/S0022336000034922. ISSN   0022-3360.
  11. 1 2 Carrol, Robert L.; Carrol, Robert L. (1998). Vertebrate paleontology and evolution. Includes Index: 1. Vertebrates, Fossil. 2. Vertebrates-Evolution. I. Title. New York: Freeman. ISBN   978-0-7167-1822-2.
  12. 1 2 Laan, Richard van der (2018-10-11). "Family-group names of fossil fishes". European Journal of Taxonomy (466). doi: 10.5852/ejt.2018.466 . ISSN   2118-9773.
  13. ↑ Nelson, Joseph S.; Wilson, Mark V. H.; Grande, Terry (2016). Fishes of the world (5th ed.). Hoboken, New Jersey: John Wiley & Sons. ISBN   978-1-118-34233-6.
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