The actinopterygians are the group of fishes ancestral to all the ray-finned fishes. Everything from the seahorse up to tuna belongs to the ray-finned fishes, some 20,000 or more species.
The only actinopterygian found in the Middle Devonian sediments of Orkney is the species Cheirolepis trailli. This species is one of the earliest articulated examples found from this group and is described in several publications. A bit later in time (Givetian, Upper middle Devonian) is Stegotrachelis finlayi, a species found on Shetland.
Cheirolepis was a slender fish with one dorsal fin and jaws with rows of tiny but sharp teeth. The probably had to share the lake with the other top predators.
The head is covered with medium sized bony plates, with the body covered with bony scales with sharp ridges on the surface. The scales are generally smaller than one millimetre. The scales of most palaeozoic actinopterygians are covered with ganoine, a very hard enamel-like substance sometimes found in layers. The definition of ganoine differs in publications but most agree on that the structure strongly resembles enamel or enameloid. Ganoine can also be found in some Mesozoic actinopterygians and even in several recent species.
The term cosmine was introduced By Williamson in 1849 to describe the top layer of the scales of Lepidotus and palaeoniscoid actinopterygians. Later Goodrich 1907 restricted cosmine for sarcopterygians with ganoine was used for actinopterygians.
According to Friedman and Brazeau (2010) “Multilayered enamel occurs only in ganoine, even partial overlap of enamel is only found in ganoine.”
According to Schultze (2016):
Thus, ganoine can be defined as multilayered or partially overlapping enamel with a tuberculated surface in Mesozoic and Recent ganoid scales.
Cosmine is a combination of tissues and one structure a single thin layer of “true” enamel covers dentine interrupted by pores of the pore–canal system.
Morphology and histology
The tiny scales of Cheirolepis have a bony base with often several layers of enamel on top of each other, the ganoid type. The whole scale lies beneath the skin with only the enamel visible on the outside. The base of the scale is made up of isopedin and the scale grows by adding a layer concentrically. Also, the head plates and the finrays are having a histology that looks much like the one seen in the scales. In the isopedin cell lacunae are visible. In later forms the ganoin is often not present.
References for Ganoine, Cosmine:
- Borgen U.J Cosmine resorption structures on three osteolepid jaws and their biological significance Lethaia, 22 (1989), pp. 413-424
- Campbell K.S.W, R.E. Barwick, T.J. Senden Perforations and tubules in the snout region of Devonian dipnoans E.D. Elliott, J.C. Maisey, X. Yu, D. Miao (Eds.), Phylogeny and Paleobiogeography of Fossil Fishes, Verlag Dr. F. Pfeil, München (2010), pp. 325-361
- Friedman M., M.D. Brazeau A reappraisal of the origin and basal radiation of the Osteichthyes J. Vertebr. Paleontol., 30 (1) (2010), pp. 36-56
- Gross W. Kleine Schuppenkunde N. Jb. Geol. Paläontol. Abh., 125 (1966), pp. 29-48
- Meinke, D,K., A Review of Cosmine: Its Structure, Development, and Relationship to Other Forms of the Dermal Skeleton in Osteichthyans, Journal of Vertebrate Paleontology, Vol. 4, No. 3, Essays Presented to Dr. Bobb Schaeffer (Nov., 1984), pp. 457-470
- Miles, E.A.W., R.C. Greulich (Eds.), Structural and Chemical Organization of Teeth 1, Academic Press, New York, London (1967), pp. 45-110
- MondéJar-Fernández, J.,2018, On Cosmine : its origins, biology and implications for sarcopterygian interrelationships, Cybium 2018, 42(1):41-65
- Ørvig, T., Histologic studies of Placoderms and fossil Elasmobranchs. I: The endoskeleton, with remarks on the hard tissues of lower vertebrates in general
- Zool., 2 (2) (1951), pp. 321-454
- Ørvig, T., Phylogeny of tooth tissues: evolution of some calcified tissues in early vertebrates
- Qu Qingming, Tatjana Haitina, Min Zhu, Per Erik Ahlberg, New genomic and fossil data illuminating the origin of enamel. Nature, vol.526, 1 October 2015 p:108-111
- Smith MM. Distribution and variation in enamel structure in the oral teeth of sacopterygians: its significance for the evolution of a protoprismatic enamel. Historical Biol 3: 97-126, 1989
- Schmidt WJ, Keil A (1971) Polarizing microscopy of dental tissues. Pergamon, Oxford
- Smith, M.M., 1977. The microstructure of the dentition and dermal ornament of three dipnoans from the Devonian of Western Australia: a contribution towards dipnoan interrelations, and morphogenesis, growth andadaptation of the skeletal tissues. PhilosophicalTransactions of the Royal Society of London (B) 281:29-72.
- Smith MM, Hall BK. Development and evolutionary origins of vertebrate skeletogenic and odontogenic tissues. Biol Rev 1990;65 277-3.
- Smith MM (1992) Microstructure and evolution of enamel amongst osteichthyan fishes and early tetrapods. In: Smith P, Tchernov E (eds) Structure, function and evolution of teeth. freund, London,pp 73–101
- Smith MM, Hall BK (1990) Development and evolutionary origins of vertebrate skeletogenic and odontogenic tissues. Biol Rev 65:277–373
- Schultze, H.P. , Scales, Enamel, Cosmine, Ganoine, and early Osteichthyans, Compte rendu Palevol. Volume 15, Issues 1–2, January 2016, Pages 83-102
- -Thomson, K.S., On the individual history of cosmine and a possible electroreceptive function of the pore–canal system in fossil fishes S.M. Andrews, R.S. Miles, A.D. Walker (Eds.), Problems in Vertebrate Evolution, Academic Press, London (1977), pp. 247-270
- Zhu, M., W. Wang, X. Yu Meemannia eos, a basal sarcopterygian fish from the Lower Devonian of China – expanded description and significance E.D. Elliott, J.C. Maisey, X. Yu, D. Miao (Eds.), Phylogeny and Paleobiogeography of Fossil Fishes, Verlag Dr. F. Pfeil, München (2010), pp. 199-214
- Zhu, M., W. Zhao, L. Jia, J. Lu, T. Qiao, Q. Qu -The oldest articulated osteichthyan reveals mosaic gnathostome characters Nature, 458 (2009), pp. 469-474
References for actinopterygians:
- Clement A.M., Benedict King, , Sam Giles5, Brian Choo,Per E Ahlberg, Gavin C. Young, John A. Long, Neurocranial anatomy of an enigmatic Early Devonian fish sheds light on early osteichthyan evolution, eLife 7:e34349 (2018)
- Choo, B. , Jing LU, Sam Giles , Kate Trinajstic and John A. Long, A new actinopterygian from the late Devonian Gogo formation. Western Australia, Papers in Palaeontology, Vol. 5, Part 2, 2019, pp. 343–364]
- Gardiner, B. G. 1984. The relationships of the palaeoniscid fishes, a review based on new specimens of Mimia and Moythomasia from the Upper Devonian of Western Australia. Brit. Mus. Nat. Hist. (Geol.) 37, 173-428, figs. 1-147, pls. 1-5.
- Giles S., Kara Feilich , Stephanie Pierce , Matt Friedman, (2021) High lineage survivorship across the end-Devonian Mass Extinction suggested by a remarkable new Late Devonian actinopterygian.
- Henderson, S., Dunne, E., Giles,S. (2023?)The early diversification of ray-finned fishes (Actinopterygii): hypotheses, challenges and future prospects (submitted)
- Lehman, J.-P. 1947 Description de quelgues exemplaires de Cheirolepis canadensis (Whiteaves). Svenska VetenskAkad. Handl., 24, 1-40, figs. 1-22, pls. 1-9.
- Newman, M.J., Carole J. Burrow, Jan L. den Blaauwen & Sam Giles (2021) A new actinopterygian Cheirolepis jonesi nov. sp. from the Givetian of Spitsbergen,
Svalbard, Norwegian Journal of Geol.
- Orvig, T. 1978. Microstructure and growth of the dermal skeleton in fossil actinopterygian fishes: Birgeria and Scanilepis. Scripta, 7, 33-56, figs. 1-35.
- Orvig, T. 1978. Microstructure and growth of the dermal skeleton in fossil actinopterygian fishes: Boreosomus, Plegmolepis and Gyrolepis. Scripta, 7, 125-44, figs. 1-29.
- Orvig, T. 1978. Microstructure and growth of the dermal skeleton in fossil actinopterygian fishes: Nephrotus and Colobodus, with remarks on the dentition in other forms. Scripta, 7, 297-326, figs. 1-67.
- Pearson, D. M. and Westoll, T. S. 1979. The Devonian actinopterygian Cheirolepis Transactions of the Royal Society of Edinburgh, 70, 337-399.
- Powrie, J. 1867. On the genus Cheirolepis, from the Old Red Sandstone. Mag., IV, 147-152, 2 figs.
- Swartz, B. A. 2009. Devonian actinopterygians phylogeny and evolution based on a re-description of Stegotrachelus finlayi. Zoological Journal of the Linnean Society, 156, 750-784.
- Traquair, R. H. 1875. On the structure and systematic position of the genus Cheirolepis. Mag. Nat. His., (4) XV, 237 – 248, pl. XVII.
- Watson, D. M. S. 1925. The structure of certain palaeoniscids and the relationships of that group with other bony fish. Zool. Soc. London, LIV, 815-870, figs. 1-30, pls. I, II.