Gyroptychius was a predator whose fossils are exclusively found in Middle to Upper Devonian layers. Gyroptychius is a well-known genus of the family Osteolepididae. It had two dorsal fins toward the back of its body and a rhombus-shaped caudal fin (Frickhinger, 1995). Its jaws were relatively short, which enabled a powerful bite (Dineley and Metcalf, 1999). The tail fin was nearly symmetrical, which helps distinguish this species from other, similar fish in Devonian sediments. The scales and body were covered with a thin, porous bony layer called cosmine (Mondéjar-Fernández, 2018). It is a member of the lobe-finned group of fish, and seems to have lived in fresh water environments (Dineley and Metcalf, 1999). The fish shown here is from northern Scotland; other examples of the genus have been found in Belarus, Estonia, Latvia, and Germany, and they are restricted to Devonian sediments (Paleobiology Database, n.d.).

References:

Dineley, D.L. and Metcalf, S.J. (1999) Fossil Fishes of Great Britain. Peterborough: Joint Nature Conservation Committee. Ch. 6.

Frickhinger, K.A. (1995) Fossil Atlas, fishes Karl Albert Frickhinger. transl. by R. P. S. Jefferies. Blacksburg, VA: Mergus, Publ. for Natural History and Pet Books Baensch Tetra Press. p. 968.

Gyroptychius agassizi (2022) Landscapes of Orkney. Available at: https://orkneylandscapes.org/orkney/millerosteus-minor/ (Accessed: 20 August 2024).

MondéJar-Fernández, J., (2018) On cosmine: its origins, biology and implications for sarcopterygian interrelationships. Cybium, 42(1), pp. 41-65.

Paleobiology Database (no date) Gyroptychius, The Paleobiology Database. Available at: https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=txn:34923 (Accessed: August 2024).