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Diplacanthus; Temporal range: Eifelian–Famennian PreꞒ Ꞓ O S D C P T J K Pg N
	Fossil specimen of D. crassissimus (=D. striatus)
	Life restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	†Acanthodii
Order:	†Diplacanthiformes
Family:	†Diplacanthidae
Genus:	†Diplacanthus; Agassiz, 1843
Species
	see text

Diplacanthus is an extinct genus of Mid to Late Devonian fish in the class Acanthodii, known as spiny sharks.

Classification

The genus was named by Louis Agassiz in 1843.^[1] It was formerly regarded as belonging to the Climatiformes but recently reassigned to the Diplacanthiformes, in which it is united with, amongst others, Rhadinacanthus, Uraniacanthus, and Culmacanthus. Diplacanthiforms were widespread during the Middle and early Late Devonian. They are best represented in the Middle Devonian, by articulated fossils, fin spines, and abundant scales, the latter particularly from northern Europe.^[2]

In a latest revision of the genus Diplacanthus, a large number of species from Europe were synonymized with earlier Scottish species, and these too were redefined. D. crassisimus was taken to have precedence over D. striatus as the name of the type specimen. Diplacanthus longispinus was reassigned to Rhadinacanthus longispinus, within which were also included Diplacanthus horridus (Woodward, 1892) and Diplacanthus ellsi. Diplacanthus tenuistriatus and Diplacanthus kleesmentae were however retained. Non-Laurussian species such as Diplacanthus acus from South Africa were not considered in this review.^[2]

Species

†D. acus Gess, 2001
†D. crassisimus Duff, 1842 (type species)
†D. gravis? Valiukevičius, 1986
†D. kleesmentae? Valiukevičius, 1988
†D. poltnigi? Valiukevičius, 2003
†D. solidus? Valiukevičius, 1986
†D. tenuistriatus Traquair, 1844

Fossil (left) and life restoration of D. acus

Diplacanthus acus is described from a near complete whole-bodied impression discovered in 1999 during roadworks cutting the Waterloo Farm lagerstätte in South Africa.^[3] The type specimen of Diplacanthus acus is approximately 100 mm long and has exceptionally long and thin ribbed spines. The intermediate spines are, conversely, extremely reduced.^[4] Unusually it preserves complete outlines of many of the fins.

Diplacanthus is most commonly associated with deposits traditionally interpreted as fresh water. However, Waterloo Farm is interpreted as estuarine in origin, as is the Canadian Miguashaia lagerstätte from which two species of Diplacanthus have been described.^[5] The description of Diplacanthus acus provided the first record of a diplacanthid from the Famennian, with diplacanthids having previously been thought to have gone extinct by the end of the Frasnian.^[6]

References

^ "Diplacanthus". The Paleaobiology Database.
^ ^a ^b Burrow, Carole; Blaauwen, Jan den; Newman, Michael; Davidson, Robert. "The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland". Palaeontologia Electronica. 19 (1): 1–83. doi:10.26879/601. ISSN 1094-8074.
^ Gess, Robert W. and Whitfield Alan K. (2020). "Estuarine fish and tetrapod evolution: Insights from a Late Devonian (Famennian) Gondwanan estuarine lake and a southern African Holocene equivalent". Biological Reviews. doi:10.1111/brv.12590. PMID 32059074
^ Gees, Robert W. (2001-01-01). "A new species of Diplacanthus from the Late Devonian (Famennian) of South Africa". Annales de Paléontologie. 87 (1): 49–60. doi:10.1016/S0753-3969(01)88002-2. ISSN 0753-3969.
^ Gess, R. and Coates M. (2008). Vertebrate Diversity of the Late Devonian (Famennian) Deposit near Grahamstown, South Africa. Journal of Vertebrate Paleontology: 28 (3) conference supplement p 83.
^ Janvier, P.(1996). Early Vertebrates. Oxford University Press, Oxford.