Symmorium Explained

Symmorium is a dubious genus of extinct stethacanthid cartilaginous fish from the Devonian and Carboniferous of the United States (Illinois)^{[1] [2]} and Russia.^[3] The type species, Symmorium reniforme, was named by Edward Drinker Cope in 1893^[4] and several other species were originally classed under this genus, but they have since been classified into other genera such as Petalodus. Symmorium bears close similarity in size and appearance to Stethacanthus^[5] but the former is missing the "spine and brush" on its back. Some paleontologists think that the two forms are simply the males and females of related species, while other scientists think they were distinct genera.^{[6] [7]}

Notes and References

1. E. D. Cope. 1894. New and little known Paleozoic and Mesozoic fishes. Journal of the Academy of Natural Sciences Philadelphia (Series 2) 9:427-448
2. M. E. Williams. 1985. The "Cladodont level" sharks of the Pennsylvanian black shales of central North America. Palaeontographica Abteilung A 190:83-158
3. A. Ivanov. 1999. Late Devonian - Early Permian chondrichthyans of the Russian Arctic. Acta Palaeontologica Polonica 49(3):267-285
4. E. D. Cope. 1893. On Symmorium, and the position of cladodont sharks. American Naturalist 27:999-1001
5. Web site: Hierarchical Taxonomy of the Class Chondrichthyes . comenius.susqu.edu . 12 January 2022 . https://web.archive.org/web/20070927011823/http://comenius.susqu.edu/biol/202/Animals/DEUTEROSTOMES/CRANIATA/CHONDRICHTHYES.htm . 27 September 2007 . dead.
6. M. Ginter, O. Hampe, and C. J. Duffin. 2010. Chondrichthyes, Paleozoic Elasmobranchii: Teeth. In H.P. Schultze (ed.), Handbook of Paleoichthyology 3D:1-168
7. Coates. Michael I.. Gess. Robert W.. Finarelli. John A.. Criswell. Katharine E.. Tietjen. Kristen. A symmoriiform chondrichthyan braincase and the origin of chimaeroid fishes. Nature. en. 541. 7636. 208–211. 2017. 10.1038/nature20806. 28052054. 2017Natur.541..208C. 4455946. 0028-0836. subscription.