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== thumb|left|upright=2|Complete skeleton of Akmonistion| Akmonistion zangerli (HMV8246, Hunterian Museum, University of Glasgow). Photograph taken by Dr. Keith Ingham, published in Coates & Sequira, 2001. 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 established by Newberry (1889) 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 and the Devonian and Mississippian of Ohio, were not described until a century later. The Family Stethacanthidae was described by Richard Lund in 1974, 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). Further reports of material attributed to Stethacanthus have extended its range to the Mississippian of Oklahoma, the Lower Tournaisian of Central Russia and the basal Namurian/Serpukhovian of Scotland.