Ctenacanthiformes is an extinct order of cartilaginous fish. They possessed ornamented fin spines at the front of their dorsal fins and cladodont-type dentition,[1] that is typically of a grasping morphology, though some taxa developed cutting and gouging tooth morphologies.[2] Some ctenacanths are thought to have reached sizes comparable to the great white shark, with body lengths of up to 7 metres (23 ft) and weights of 1,500–2,500 kilograms (3,300–5,500 lb).[3] The earliest ctenacanths appeared during the Frasnian stage of the Late Devonian (~383-372 million years ago), with the group reaching their greatest diversity during the Early Carboniferous (Mississippian), and continued to exist into at least the Middle Permian (Guadalupian).[4] Some authors have suggested members of the family Ctenacanthidae may have survived into the Cretaceous based on teeth found in deep water deposits of Valanginian age in France[5] and Austria,[6] however, other authors contend that the similarity of these teeth to Paleozoic ctenacanths is only superficial, and they likely belong to neoselachians instead.[7]
Ctenacanthiformes are suggested to be more closely related to living elasmobranchs (modern sharks and rays) than to Holocephali (which includes living chimaeras).[8] The monophyly of the Ctenacanthiformes has been questioned, with some studies recovering the group as a whole as paraphyletic or polyphyletic with respect to other groups of total group elasmobranchs like Xenacanthiformes.[9]
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