Helodus
| Helodus Temporal range:
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|---|---|
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| Tooth file of Helodus simplex | |
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| Life restoration of Helodus simplex | |
Scientific classification 
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Chondrichthyes |
| Subclass: | Holocephali |
| Order: | †Helodontiformes |
| Family: | †Helodontidae |
| Genus: | †Helodus Agassiz, 1838 |
| Type species | |
| Helodus simplex Agassiz, 1838
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| Synonyms | |
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Helodus (from Greek: ἧλος helos, 'stud' and Greek: ὀδούς odoús 'tooth')[1] is an extinct genus of cartilaginous fish from the Upper Devonian through Lower Permian.[2] While the type species, H. simplex from the Late Carboniferous (Moscovian ~ 315 million years ago)[3] of England is known from articulated specimens, the rest of the species in this genus are known only from isolated teeth.[4] Over seventy species have been attributed to this genus, many of which may be anterior teeth of other cartilaginous fish. This makes Helodus as broadly defined a wastebasket taxon.[5]: 53–60 Only the type species can be confidently attributed to this genus until articulated remains of other species are found.[4] H. simplex was around 30 centimeters (1 foot) long,[2] and males had a large, tooth-bearing clasping organ on their heads. The teeth of H. simplex, which were arranged in tooth-whorls, were transitional between elasmobranch-like separated teeth and the tooth plates of living chimaeras.[3]
Research history
[edit]The genus Helodus was named by naturalist Louis Agassiz in 1838 to refer to isolated bead-like teeth from the late Paleozoic. Parts of the cartilaginous skeleton were first described in 1890.[6][7]
References
[edit]- ^ Roberts, George (1839). An etymological and explanatory dictionary of the terms and language of geology. London: Longman, Orme, Brown, Green, & Longmans. p. 76. Retrieved 30 December 2021.
- ^ a b Arno Hermann Müller: Textbook of paleozoology. Volume III, Vertebrates, Part 1. Gustav Fischer Verlag, 1985.
- ^ a b Cohen, Karly E.; Coates, Michael I.; Fraser, Gareth J. (2025). "Teeth outside the jaw: Evolution and development of the toothed head clasper in chimaeras". Proceedings of the National Academy of Sciences. 122 (37). doi:10.1073/pnas.2508054122. PMC 12452905.
- ^ a b Itano, W.M., Lambert, L.L. A new cochliodont anterior tooth plate from the Mississippian of Alabama (USA) having implications for the origin of tooth plates from tooth files. Zoological Lett 4, 12 (2018). doi:10.1186/s40851-018-0097-8
- ^ Stahl, Barbara J. (1999). Handbook of Paleoichthyology: Chondrichthyes III, Holocephali. Vol. 4. München: Pfeil. ISBN 978-3-931516-63-5.
- ^ Coates, Michael; Tietjen, Kristen; Johanson, Zerina; Friedman, Matt; Sang, Stephanie (2021). Pradel, Alan; Denton, John S. S.; Janvier, Philippe; Maisey, John G. (eds.). The cranium of Helodus simplex (Agassiz, 1838) revised. Ancient fishes and their living relatives: a tribute to John G. Maisey. München: Verlag Dr. Friedrich Pfeil. pp. 193–204. ISBN 978-3-89937-269-4.
- ^ Johanson, Zerina; Underwood, Charlie; Coates, Michael; Fernandez, Vincent; Clark, Brett; Smith, Moya M. (2021). Pradel, Alan; Denton, John S. S.; Janvier, Philippe; Maisey, John G. (eds.). The stem-holocephalan Helodus (Chondrichthyes; Holocephali) and the evolution of modern chimaeroid dentitions. Ancient fishes and their living relatives: a tribute to John G. Maisey. München: Verlag Dr. Friedrich Pfeil. pp. 205–214. ISBN 978-3-89937-269-4.
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