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Stethacanthidae
Stethacanthidae is an extinct family of prehistoric sharks. It is estimated to have existed approximately between 380 and 300 million years ago. Members of this family are noted for their peculiar dorsal fin.
==Introduction==
The taxonomic history of the Family Stethacanthidae has been rather complicated because the findings of complete skeletons are very unusual, and as result early workers such as St.. John & Worthen,〔 and Newberry〔 were unable to recognise the association of the spine, dentition teeth, and dermal denticles of these sharks. The genus ''Stethacanthus'' was stablished by Newberry (1889)〔NEWBERRY, J.S., 1889. The Paleozoic fishes of North America. ''United States Geological Survey Monograph'', 16, 340pp.〕 for a series of large thin walled, cartilage-cored spines encountered in Mississippian (Carboniferous Period) rocks of the mid-continental United States. Decomposition of the internal cartilage and compression during burial resulted in distortion of the spines, leading Newberry to misinterpret them, he believed that the spines belonged to pectoral and pelvic fins of a new species of shark. The first associated skeletal remains, from the Mississippian of Montana〔〔LUND, R., 1985a. Stethacanthid elasmobranch remains from the Bear Gulch Limestone (Namurian E2b) of Montana. ''American Museum Noviates'', 2828, 1-24〕 and the Devonian and Mississippian of Ohio,〔WILLIAMS, M.E., 1985. The «cladodont level» sharks of the Pennsylvanian black shales of central North America. ''Palaeontographica Band A, Stuttgart'', 190, 83-158〕〔ZANGERL, R., 1981. Chondrichthyes I: Paleozoic Elasmobranchii. H.P. Schultze (ed.), ''Handbook of Paleoichthyology, New York'', 115pp〕 were not described until a century later. The Family Stethacanthidae was described by Richard Lund in 1974,〔LUND, R., 1974. ''Stethacanthus altonensis'' (Elasmobranchii) from the Bear Gulch Limestone of Montana. ''Annals of Carnegie museum'', 45(8), 161-178〕 he argued that "''Stethacanthus'' represents an experiment in elasmobranch evolution that is significantly divergent enough to warrant family-level separation". This classification was later corroborated by another authors (e.g. Zangerl,1990〔ZANGERL, R., 1990. Two new stethacanthid sharks (''Stethacanthidae, Symmoriida'') from the Pennsylvanian of Indiana, USA. ''Palaeontographica Band A'', 213, 115-141〕). Further reports to of material attributed to ''Stethacanthus'' have extended its range to the Mississippian of Oklahoma,〔ZIDEK, J., 1993. A large ''stethacanthid'' shark (Elasmobranchii, Symmoriida) from the Mississippian of Oklahoma. ''Oklahoma Geology Notes'', 53, 4-15〕 the Lower Tournaisian of Central Russia〔LEBDEV, O.A., 1996. Fish assemblages of the Tounaisian-Viséan environments of the East European Platform. ''Geological Society Special Publication'', 107, 387-415〕 and the basal Namurian/Serpukhovian of Scotland.〔〔
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