Ctenacanthiformes

Ctenacanthiformes; Temporal range: 383–259 Ma PreꞒ Ꞓ O S D C P T J K Pg N Late Devonian— Middle Permian (Possible Valanginian record)
	Life restoration of Dracopristis
	Fin spine of Ctenacanthus formosus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	†Ctenacanthiformes; Glikman, 1964
Subtaxa
	See text
Synonyms
	Ctenacanthida Cappetta (1988);

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] while others reached lengths of only 30 centimetres (12 in).^[4] 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]

Taxonomy

Ctenacanthiformes are suggested to be more closely related to living elasmobranchs (modern sharks and rays) than to Holocephali (which includes living chimaeras), though less closely than euselachians like hybodonts.^[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]

Following Hodnett et al. 2024^[4]

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 (Early Carboniferous)
Bythiacanthus St. John and Worthen 1875 (Early Carboniferous)
Dracopristis Hodnett et al. 2021 (Late Carboniferous)
Glencartius Ginter and Skompski 2019 (Early Carboniferous)
Glikmanius Ginter et al. 2005 (Early Carboniferous-Middle Permian)
Heslerodus Ginter 2002 (Late Carboniferous-Middle Permian)
Heslerodoides Ivanov 2022 (Late Carboniferous)
Kaibabvenator Hodnett et al. 2012 (Early-Middle Permian)
Nanoskalme Hodnett et al. 2012 (Early-Middle Permian)

"Saivodus group"

Tamiobatis Eastman, 1897 (Late Devonian-Early Carboniferous)
Saivodus Duffin & Ginter, 2006 (Early Carboniferous-Middle Permian, one of the largest ctenacanths, estimated to reach 6–8 metres (20–26 ft) in length^[4])
Neosaivodus Hodnett et al. 2012 (Middle Permian)