Ctenacanthiformes

Ctenacanthiformes is an extinct order of cartilaginous fish. They possessed ornamented fin spines at the front of their dorsal fins and cladodont-type dentition, that is typically of a grasping morphology, though some taxa developed cutting and gouging tooth morphologies. Some ctenacanths are thought to have reached sizes comparable to the great white shark, with body lengths of up to 7 m and weights of 1500-2500 kg. 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). 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 and Austria, however, other authors contend that the similarity of these teeth to Paleozoic ctenacanths is only superficial, and they likely belong to neoselachians instead.

Taxonomy
Ctenacanthiformes are suggested to be more closely related to living elasmobranchs (modern sharks and rays) than to Holocephali (which includes living chimaeras). 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.

Following Hodnett et al. 2024

Ctenacanthidae Dean 1909


 * Ctenacanthus Agassiz, 1837 (Late Devonian)
 * Cladodoides Maisey, 2001 (Late Devonian-Early Carboniferous)
 * Cladodus Agassiz, 1843 (Early Carboniferous)
 * Goodrichthys Moy-Thomas, 1951 (Early Carboniferous)
 * Troglocladodus Hodnett et al. 2024 (Early Carboniferous)

Heslerodidae Maisey 2010


 * Avonacanthus Maisey 2010
 * Bythiacanthus St. John and Worthen 1875
 * Dracopristis Hodnett et al. 2021
 * Glencartius Ginter and Skompski 2019
 * Glikmanius Ginter et al. 2005
 * Heslerodus Ginter 2002
 * Heslerodoides Ivanov 2022
 * Kaibabvenator Hodnett et al. 2012
 * Nanoskalme Hodnett et al. 2012

"Saivodus group"


 * Tamiobatis Eastman, 1897
 * Saivodus Duffin & Ginter, 2006
 * Neosaivodus Hodnett et al. 2012