Acanthodians are relatives of sharks and include the ancestors of the latter. They are characterized by having spines on all their fins. Acanthodians are all extinct - most were wiped out at the end of the Devonian, but a few groups staggered on for another 100 million years until the end of the Permian.
Gyracanthides riniensis
Locality: Waterloo Farm Age: latest Devonian This species is described on the basis of fin spines, bones of the shoulder girdle and skin impressions, most found in an association suggesting that they came from a single individual (1). The spines include pectoral, pelvic and median fin spines, that may either be anal or dorsal fin spines. It is distinguished from other Gyracanthides species by its distinctive median spines and the nature of its spine ridge ornament. Curiously one of the pectoral spin fines has been broken in two equal halves prior to deposition on a shale bedding plane (see image above). Damage during predation appears to provide the only plausible explanation. Gyracanthides was a relatively large acanthodian, adults reaching over a metre in length. It has a distinctive ‘gyrating’ ornamentation on the fin spines. Several records of gyracanthids are known from non-marine deposits, indicating that this group may have preferred freshwater. Gyracanthid acanthodians are known throughout the Devonian Period, but became particularly widespread in the Early Carboniferous Period. The Waterloo Farm species is very similar to ‘Gyracanthus’ sherwoodi from the Red Hill locality in the Catskill Formation, which is likewise Late Famennian in age. This comes as no surprise because these two localities, one in South Africa and the other in North America, share a great deal of vertebrate diversity, including the only known records of the tristicopterid Hyneria. Other taxonomic overlaps between these sites include antiarch placoderms (Bothriolepis), arthrodire placoderms (Groenlandaspis and Africanaspis/Turriaspis), lungfish, actinopterygians and tetrapods. Palaeogeographic proximity between southeastern Laurussia and western Gondwana is therefore indicated.
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References:
1) Gess, R. W., & Burrow, C. J. (2024). A new gyracanthid (stem Chondrichthyes) from the Late Devonian (Famennian) of the Eastern Cape, South Africa. Journal of Vertebrate Paleontology, e2305888.
2) Gess, R. W., (2001) A new species of Diplacanthus from the Late Devonian (Famennian) of South Africa. Ann. PaIaeontol. 87, 1, 49-60
1) Gess, R. W., & Burrow, C. J. (2024). A new gyracanthid (stem Chondrichthyes) from the Late Devonian (Famennian) of the Eastern Cape, South Africa. Journal of Vertebrate Paleontology, e2305888.
2) Gess, R. W., (2001) A new species of Diplacanthus from the Late Devonian (Famennian) of South Africa. Ann. PaIaeontol. 87, 1, 49-60