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Ctenoptychius

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Ctenoptychius
The holotype tooth of C. apicalis, figured by Louis Agassiz in Recherches sur les poissons fossiles
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Holocephali
Order: †Petalodontiformes
Family: †Belantseidae
Genus: †Ctenoptychius
(Agassiz, 1838)
Type species
Ctenoptychius apicalis
Species synonyms
  • C. stevensoni?

Ctenoptychius (meaning "comb-folded", from the Greek κτείς or kteís meaning "comb" and πτυχή or ptychos meaning "fold")[1] is an extinct genus of cartilaginous fish in the order Petalodontiformes. While Ctenoptychius was historically thought to encompass a large number of species with serrated tooth crowns, it is now considered to include only the type species, C. apicalis. This species lived during the Late Carboniferous period, and its fossils are known from the United Kingdom and potentially the United States. C. apicalis is known primarily from teeth, which have a flattened shape and serrated edges, although poorly-preserved specimens preserving the head, pectoral fins and scales of the body are also known. Based on this, it is believed that Ctenoptychius had a flattened, ray-like body.

Discovery and classification

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Plate from Recherces sur les poissons fossiles, in which Ctenoptychius was described. Fig. 1 and 1a represent C. apicalis, while fig. 2-7 represent other species then assigned to the genus[2]

Ctenoptychius was named by naturalist Louis Agassiz in his work Recherches sur les poissons fossiles.[2][3][4] Agassiz considered the genus to encompass three species: C. apicalis, C. denticulatus, and C. pectinatus, with C. apicalis being the type species. All three species were diagnosed based on isolated teeth from the Carboniferous of England, and were united by the presence of large serrations on the tooth crown.[2][4][5] Subsequent authors have assigned additional species based on tooth-like structures with similar serrations, including fossils that have since been identified as the sex organs of the tetrapodomorph Ophiderpeton.[3][6][7] Large serrations or cusplets are now known to occur in many unrelated genera of Paleozoic chondrichthyan, only C. apicalis is considered a member of the genus, and other species have been reassigned to different genera or,[4][5][8] as in the North American "C. stevensoni", have been regarded as probable synonyms of the type species.[5] The holotype tooth of C. apicalis is now missing.[4]

Articulated body fossils of Ctenoptychius apicalis were described from the coal measures of North Staffordshire in 1890. These preserve the front portion of the body and pectoral fins, the coating of dermal denticles, the cartilaginous jaws, and disarticulated teeth.[3][8][9] However, the preservation of this material has been noted as poor, and details of the anatomy are difficult to make out.[3][8]

The taxon "Ctenoptychius" korni is known from complete, articulated body fossils from the Late Permian-age Kupferschiefer of Germany.[10][11][12] This species has variously been assigned to Ctenoptychius and the distantly related genus Janassa, but has alternatively been suggested to belong to neither due to lacking the distinctive features of both genera.[12]

Description

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Reconstruction of C. apicalis based on Janassa, which it is assumed to have closely resembled.[13] Unpreserved regions are represented by dashed lines

The tooth crowns of Ctenoptychius apicalis had between three and nine cusplets, with the centermost being the largest. The root (or base) of the tooth was wide and rounded.[5][8] The overall shape of the teeth was flattened.[14] In life, the teeth were arranged in multiple tightly packed rows in the upper and lower jaws.[13]

The body of Ctenoptychius was depressiform and the pectoral fins were large and broad.[8][14][13] The body shape was similar to a living ray or angelshark,[8][13][15] as well as to the distantly related Janassa bituminosa which the head and fins of Ctenoptychius closely resembled. Nothing is known about the dorsal fin or pelvic fin anatomy of C. apicalis,[13] but there is no evidence of defensive spines on the dorsal fin.[3][14] The known portion of the body was coated by dermal denticles, which were most numerous around the head. The anatomy of the denticles is not known in detail.[3]

Paleoecology

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Due to its ray-like shape, Ctenoptychius is assumed to have been a bottom-dweller. Petalodont fossils are known primarily from shallow marine environments, and the stomach contents of Janassa imply that at least some members of the group were omnivorous bottom feeders that targeted hard-shelled invertebrates.[15]

See also

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References

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  1. ^ Roberts, George (1839). An etymological and explanatory dictionary of the terms and language of geology. London: Longman, Orme, Brown, Green, & Longmans. p. 38. Retrieved 31 December 2021.
  2. ^ a b c Agassiz, Louis; Agassiz, Louis (1833). Recherches sur les poissons fossiles ... Neuchatel: Petitpierre. doi:10.5962/bhl.title.4275.
  3. ^ a b c d e f W, A. S. (1890). "III.—The Geological Features of the North Staffordshire Coal-Fields, their Organic Remains, their Range and Distribution; with a Catalogue of the Fossils of the Carboniferous System of North Staffordshire". Geological Magazine. 7 (9): 141–152. doi:10.1017/S0016756800188144. ISSN 1469-5081.
  4. ^ a b c d Downs, Jason Philip; and Daeschler, Edward B. (2001-12-14). "Variation within a large sample of Ageleodus pectinatus teeth (Chondrichthyes) from the Late devonian of Pennsylvania, U.S.A." Journal of Vertebrate Paleontology. 21 (4): 811–814. doi:10.1671/0272-4634(2001)021[0811:VWALSO]2.0.CO;2. ISSN 0272-4634.
  5. ^ a b c d Ginter, Michał; Hampe, Oliver; Duffin, Christopher J. (2010). Handbook of paleoichthyology: teeth. München: F. Pfeil. pp. 147–150. ISBN 978-3-89937-116-1.
  6. ^ Moodie, Roy L. (1908). "THE CLASPING ORGANS OF EXTINCT AND RECENT AMPHIBIA". The Biological Bulletin. 14 (4): 249–259. doi:10.2307/1535616. ISSN 0006-3185.
  7. ^ Catalogue of the fossil fishes in the British Museum (Natural History). Vol. 1. London: British Museum of Natural History. 1889. p. 155. doi:10.5962/bhl.title.61854.
  8. ^ a b c d e f Zangerl, Rainer (1981). Chondrichthyes 1: Paleozoic Elasmobranchii. Handbook of Paleoichthyology. Friedrich Pfell (published January 1, 1981). pp. 95–97. ISBN 978-3899370454.
  9. ^ Gibson, Walcot; Barrow, George; Wedd, Charles Bertie; Ward, John (1905). The geology of the north Staffordshire coalfields. Cornell University Library. London, Printed for H. M. Stationery off., by Wyman and sons, limited. p. 298.
  10. ^ Brandt, Silvio (1996). "Janassa korni (Weigelt) — Neubeschreibung eines petalodonten Elasmobranchiers aus dem Kupferschiefer und Zechsteinkalk (Perm) von Eisleben (Sachsen-Anhalt)". Paläontologische Zeitschrift (in German). 70 (3–4): 505–520. doi:10.1007/BF02988089. ISSN 0031-0220.
  11. ^ Brandt, Silvio (2009). "Über Neufunde von Janassa korni (WEIGELT), einen petalodonten Elasmobranchier aus dem Kupferschiefer (Ober-Perm) von Eisle - ben und Sangerhausen (Sachsen-Anhalt) (About new finds and informations of the petalodontid Janassa korni from the Kupferschiefer (Upper Permian) of Eisleben and Sangerhausen, Germany)". Veröffentlichungen Naturhist. Museum Schleusingen. 24: 15–26 – via ResearchGate.
  12. ^ a b Lund, R.; Grogan, E. D.; Fath, M. (2014). "On the relationships of the Petalodontiformes (Chondrichthyes)". Paleontological Journal. 48 (9): 1015–1029. doi:10.1134/S0031030114090081. ISSN 0031-0301.
  13. ^ a b c d e Orvig, Tor, ed. (1968). Current problems of lower vertebrate phylogeny: proceedings of the 4. Nobel Symposium held in June 1967 at the Swedish Museum of Natural History (Naturhistoriska riksmuseet) in Stockholm. New York: Interscience Publ. [u.a.] pp. 153–170. ISBN 978-0-471-65713-2.
  14. ^ a b c Zittel, Karl Alfred von (1925). Text-book of paleontology. Translated by Eastman, Charles R. Internet Archive. London : Macmillan and Co. pp. 89–90.
  15. ^ a b Robb, Albert J. (2003). "Notes on the occurrence of some petalodont shark fossils from the Upper Pennsylvanian rocks of northeastern Kansas". Transactions of the Kansas Academy of Science. 106 (1 &amp, 2): 71–80. doi:10.1660/0022-8443(2003)106[0071:NOTOOS]2.0.CO;2. ISSN 0022-8443.
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