Cheiracanthus, Triazeugacanthus, Acanthodes, Menaspis and Homalacanthus

Vertebrata

Basal Chordata

Chondrichthys

Actinopterygii

Sarcopterygii

Tetrapoda

Stem and Basal Tetrapoda

Reptilia/Amniota

Lepidosauromorpha

Cephalerpeton clade

Captorhinidae

Milleretta Limnoscelis clade

Bolosaurus Diadectes clade

Turtle Pareiasaur clade

Fenestrasauria • Pterosauria

Protosquamata

Squamata

Archosauromorpha

Basal Archosauromorpha

Cheiracanthus latus (Egerton 1861; Middle Devonian; skull = NHM PV P 3253) nests with Homalacanthus in the LRT.

Triazeugacanthus affinis (Miles 1966; Early Devonian; 380 mya; up to 5.2cm) is a small acanthodian basal to all other acanthodians.

Homalacanthus concinnus (Russell 1951; 30cm, Early Devonian, 380mya) was a little crustacean eater and prey for Eusthenopteron. In the LRT this taxon is a sister to Trachinocephalus, demonstrating that spiny sharks are a grade that convergently evolve ray fins.

Menaspis armata (Ewald 1848; Late Permian; > 15cm long) was described as the 'last known arthrodire placoderm'. Here it nests with Homalocanthus, a spiny shark. The former skull spine is the pectoral fin. The former 'horns' are ventral spines. The skull and gill chamber are taphonomoca;;u missing here. So is the tail.

Acanthodes bronni (Anonymous 1880; Davis, Finarelli and Coates 2012; Early Permian 290 mya; 20cm, other species 41cm) is the latest occurring acanthodian, the largest and has the best ossified braincase. It was derived from one of the most primtiive acanthodians, Homalocanthus (above). Davis et al. mislabeled the hyomandibular as a giant quadrate and the preopercular as the mislabeled hyomandibular. Acanthodes is toothless and presumed to be a filter feeder. No extra spines are present.

Here dermal skull bones are added based on phylogenetic bracketing and bony landmarks.

Reports that acanthodians are the last common ancestors of sharks and bony fish (Friedman and Brazeau 2010, Davis, Finarelli and Coates 2012) are not supported by the LRT. Rather various spiny sharks are basal to several bony fish clades and arise from a last common ancestor close to a Silurian sister to Gregorius.

Anonymous 1880. Royal Physical Society of Edinburgh (1880). "Proceedings of the Royal Physical Society of Edinburgh". V: 115.

Burrow C, Blaauwen Jd and Newman M 2020. A redescription of the three longest-known species of the acanthodian Cheiracanthus from the Middle Devonian of Scotland. Palaeontologia Electronica 23(1):a15.

Davis SP, Finarelli JA and Coates MI 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature 486:247–250.

Egerton P de MG 1861. British fossils, pp 51-75. In Huxley TH (ed) Preliminary Essay Upon the Systematic Arrangement of the Fishes of the Devonian Epoch, Figures and Descriptions Illustrative of British Organic Remains. Memoirs of the Geological Survey UK (Decade 10).

Ewald J 1848. Über Menaspis, eine neue fossile Fischgattung. Berichte Über die zur Bekanntmachung Geeigneten Verhandlungen der Königlich-Preussischen Akademie der Wissenschaften zur Berlin 1848:33-35.

Maisey JG et al. (6 co-authors) 2018. Doliodus and Pucapampellids: Contrasting perspectives on stem chondrichthyan morphology. Chapter 5 in Evolution and Development of Fishes.

Miles RS 1966. The acanthodian fishes of the Devonian Plattenkalk of the Paffrath. Trough in the Rhineland. Arkiv för Zoologica (Stockholm)18: 147–194.

Miller RF, Cloutier R and Turner S 2003. The oldest articulated chondrichthyan from the Early Devonian period. Nature 435:501–504.

Ortlam D 1986. Neue Aspekte zur Deutung von Menaspis armata Ewald (Kupferschiefer, Zechstein 1, Deutschland) mit Hilfe der stereoskopischen Röntgentechnik. Geologisches Jahrbuch Reihe A, Band A 81.

Patterson C 1968, Menaspis and the bradyodonts. In: T. Ørvig, Current Problems of Lower Vertebrate Phylogeny. (Hrsg.): Nobel Symposium. Band 4. Almquist and Wiksell, Stockholm 1968, S. 171–205.

Russell LS 1951. XL.—Acanthodians of the upper Devonian Escumiinac formation, Maguasha, Quebec. Annals and Magazine of Natural History Series 12(4):Issue 40:410–407.

Schaumberg G 1992. Neue Informationen zu Menaspis armata Ewald. Paläontologische Zeitschrift 66:311.

Turner S and Miller RF 2004. New ideas about old sharks. American Scientist 93:244–252.

Whiteaves JF. 1881. On some fossil fishes, Crustacea and Mollusca from the Devonian rocks at Campbellton, NB, with descriptions of five new species. Can Nat 10:93–101.

Woodward AS. 1889. Acanthodian fishes from the Devonian of Canada. Ann Mag Nat Hist 4:183–184.

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