Tetrapodamorphs

Gyroptychius milleri (model by P.H.de Buisonjé)

Biostratigraphy of the tetrapodamorphs for Orkney

Gyroptychius agassizi
Gyroptychius milleri
Osteolepis macrolepidotus
Osteolepis panderi
Thursius macrolepidotus
Thursius pholidotus
Tristichopterus alatus

The tetrapodomorphs (part of the sarcopterigians (Sarcopterygii) or lobe finned fish) played an important role in the Orcadian Basin and eventually the evolution of man.

In the lake, these fast swimming fishes with their strong teeth were the top predators. They are evolutionary closely related to the first vertebrate land animals during the Upper Devonian.

The similarity of the skull, dermal skull bones and the bony structure supporting the paired fins are striking when compared with the first vertebrate land animals.

The sarcopterygians (except the dipnoans) were thought to be extinct, but in 1938 a strange fish was caught at sea in South Africa by a local fisherman. This specimen was presented to Marjorie Courtenay-Latimer who worked at the local natural history museum in East London, South Africa. Later this fish was identified by the fish expert Dr James Smith as a coelacanth. Fossil coelacanths are known from many localities and ages. The first well preserved specimens came from Germany, found in the same Jurassic limestones that are so famous for the bird-like dinosaur Archaeopteryx. This discovery had an impact on the scientific community comparable with the finding of the tomb of Tutankhamun.

The coelacanths are a member of the Actinistia which is another group of sarcopterygians. Whilst coelacanths are not found in Orkney other sarcopterygians are, like the tetrapodamorphs mentioned above. The sarcopterygians found in Orkney are grouped as:

Subclass Sarcopterygii
Infraclass Dipnomorpha
Order Porolepiformes
Subclass Dipnoi
Infraclass Tetrapodamorpha
Order Osteolepiformes
Family Osteolepididae
Family Tristichopteridae

There is no doubt anymore that the first vertebrate land animals must have evolved from the tetrapodamorphs. In the near future newly, discovered material will certainly make the picture of this step from water to land more complete.

The tetrapodamorph osteolepids (except the tristichopterids – see below) from the Middle Devonian of Orkney all have a hard, shiny layer on their bony scales called cosmine. This is composed of a layer of dentine with a thin layer on top of enameloid or enamel (depending on the publication). This layer is very hard and protects the fish against predators and harsh environmental conditions. However, if the fish grows it first needs to get rid of the cosmine. The cosmine layer is reabsorbed by the body and after that the scales can grow and a new cosmine layer is formed. The fish is vulnerable during the time of resorption and growth. Sometimes specimens are found lacking the cosmine layer.

Most likely the process of resorption and growth and formation of a new cosmine layer is a seasonal phenomenon and happens probably yearly.

See for examples in the morphology and histology below.

Tetrapodamorph fishes

Gyroptychius agassizi

The histology of Gyroptychius agassizi looks very much like the one seen in Gyroptychius milleri but the preservation in G. milleri is often better, so we only show G. milleri here.

Gyroptychius milleri

Two scales

Scales with and without cosmine

Head plate with cosmine and partly and totally resorped.

Photomicrograph of thin section of scales indicating scale histology: enamel and dentine. P= vascular boner with big pores L=laminated bone or isopedin

Scale showing yearly growth with the help of polarizing microscopy

Osteolepis macrolepidotus

Scales in a fish and in section

Osteolepis panderi

Scales of scattered fish and scales in thin section

Thursius pholidotus

Tail of Thursius pholidotus

Scattered fish

Here the enamel shows in the above picture as a thin orange line or in the one with crossed nicols only as a white line.

Again three pictures of scales in a thin section with the polarizing microscope.

Tristichopterus alatus

This species does not have a cosmine cover on the scales. The teeth have a fine linging with enamel but the scales are naked! Below some pictures of a scale on the surface and several in sections.

Tooth in the lower jaw with an enamel lining at the tip.

References sarcopterygii:

  • Ahlberg, P. E. 1989. Paired fin skeletons and the relationships of the fossil group Porolepiformes (Osteichthyes: Sarcopterygii). Zoo. Journ. Linn. Soc. London, 96, 119-166, figs. 1-16.
  • Alberg, P. E. 1989. The anatomy and phylogeny of porolepiform fishes, with special reference to Glyptolepis. University of Cambridge PhD thesis (unpublished). 369 pp.
  • Ahlberg, P. 1992. Coelacanth fins and evolution. Nature, 358, 459, Fig. 1.
  • Ahlberg, P.E., 1992, The palaeoecology and evolutionary history of the porolepiform sarcopterygians, in:Fossil fishes as living animals Ed. Elga Mark-Kurik, Tallinn.
  • Ahlberg, P. E. and Johanson, Z. 1998. Osteolepiformes and the ancestry of tetrapods. Nature, 395, 792-794, figs. 1-4.
  • Andrews, S. M. and Westoll, T. S. 1970. The postcranial skeleton of Eusthenopteron foordi Trans. Roy. Soc. Edinburgh, 68, 207-329, figs. 1-32, pls. 1-5.
  • Borgen, U. 1983. Homologizations of skull roofing bones between tetrapods and osteolepiform fishes. Palaeontology, 26, 735-753, figs. 1-7.
  • Borgen, U. J. 1989. Cosmine resorption structures on three osteolepid jaws and their biological significance. Lethaia, 22, 413-424, figs. 1-5.
  • Borgen, U. J. 1992. The function of the cosmine pore canal system. In: Fossil fishes as living animals, (ed. E. Mark-Kurik), Academia 1, Tallinn, 141-150, figs. 1-3.
  • Campbell, K. S. W. and Barwick, R. E. 1983. Early evolution of dipnoan dentitions and a new genus Speonesydrion. Mem. Ass. Australas. Palaeontol., 1, 17-49, 23 figs.
  • Campbell, K. S. W. & Barwick, R. E. 2001. Diabolepis and its relationship to the Dipnoi. Vert. Paleontol., 21, 227-241, figs. 1-7.
  • Chang, M.-M. 1991. Head exoskeleton and shoulder girdle of Youngolepis, in: Early vertebrates and related problems of evolutionary biology, ed. Chang, M.-M., Liu, Y. H. and Zhang, G. R., Science Press, Beijing. 355-378, figs. 1-16, pls. 1-6.
  • Chang, M.-M. and Min, Z. 1993. A new Middle Devonian osteolepid from Qujing, Yunnan. Ass. Australas. Palaeontols, 15, 183-198, figs. 1-14.
  • Chang, M.-M. & Smith, M. 1992. Is Youngolepis a porolepiform? Vert. Paleon., 12, 294-312, figs. 1-11.
  • Chang, M.-M. and Yu, X. 1997. Reexamination of the relationship of Middle Devonian osteolepids-fossil characters and their interpretations. Mus. Novitates, 3189, 1-20, figs. 1-4.
  • Fan, J. H. 1992. A new species of Thursius from Wuding, Yunnan. Vertbrata PalAsiatica, 30, 195-209, figs. 1-8, pls. I-III. Photocopy. (In Chinese with English summary).
  • Egerton, P. de M.G. 1861. British fossils. (Descriptions of Tristichopterus, Acanthodes, Climatius, Diplacanthus, Cheiracanthus). Memoirs of the Geological Survey of the United Kingdom (British Organic Remains), 10, 51–75.
  • Goodrich, E. S. 1919. Restorations of the head of Osteolepis. Journ. Linnean. Soc. London, XXXIV, 181-188, 6 figs.
  • Jarvik, E. 1942. On the structure of the snout of crossopterygians and lower gnathostomes in general. Bidr. Upps., 21, 235-675, figs. 1-87, pls. 1-17.
  • Jarvik, E. 1948. On the morphology and taxonomy of the Middle Devonian osteolepid fishes of Scotland. Kungliga Svenska Vetenskapsakademiens Handlinger, 25, 1-301.
  • Jarvik, E. 1944. On the dermal bones, sensory canals and pit -lines of the skull of Eusthenopteron foordi Whiteaves, with some remarks on save-soderberghi Jarvik. K. Svenska VetenskAkad. Handl., (3) 21 (3), 1-48, figs. 1-19.
  • Jarvik, E. 1949. On the Middle Devonian Crossopterygians from the Hornelen Field in Western Norway. Univ. Bergen, 1948 (Naturv.r.), 1-48, figs. 1-11, pls. 1-8.
  • Jarvik, E. 1950. Note on Middle Devonian crossopterygians from the eastern part of Gauss Halvo, East Greenland. Om Gron., 149, 20pp, figs. 1-3.
  • Jarvik, E. 1950. On some osteolepiform crossopterygians from the Upper Old Red Sandstone of Scotland. Svenska VetenskAkad. Handl., 2, 1-35, figs. 1-10, pls. I-X.
  • Jarvik, E. 1954. On the visceral skeleton in Eusthenopteron with a discussion of the parasphrnoid and palatoquadrate in fishes. Svenska VetenskAkad. Handl., (4) 5, 1-104, figs. 1-47. Paperback.
  • Jarvik, E. 1972. Middle and Upper Devonian Porolepiformes from East Greenland with special reference to Glyptolepis groenlandicasp. and a discussion on the structure of the head in the Porolepiformes. Medd. om Gron., 187, 1-307, figs. 1-108, pls. 1-35.
  • Jarvik E. 1950. Middle Devonian vertebrates from Canning Land and Wegeners Halvo (East Greenland). Part II. Crossopterygii. Meddelelser om Gronland, 96:1-132.
  • Jarvik E. 1985. Devonian osteolepiform fishes from East Greenland. Meddelelser om Gronland, Geoscience, 13:1-52.
  • Jeffery, J.E., 2001, Pectoral fins of rhizodontids and the evolution of pectoral appendages in the tetrapod stem-group, Biologicd Journal of the Linnean Society (2001), 74: 217-236.
  • Jeffery, J.E. Glenn W. Storrsb, Timothy Hollandc, Clifford J. Tabind, and Per E. Ahlberg, 2018, Unique pelvic fin in a tetrapod-like fossil fish, and the evolution of limb patterning, PNAS November 20, 2018 vol. 115 no. 47 12005–12010
  • Karatajūtė-Talimaa, V. 1963. Genus Asterolepis from the Devonian of the Russian Platform, p. 65-169. In Grigelis, A. and Karatajute-Talimaa, V. (eds). The data of geology of the Lithuania. Vilnius. [In Russian with Lithuanian and English summaries].
  • Lyarskaya L. 1981. Baltic Devonian Placodermi. Asterolepididae. Zinātne, Rīga.. [in Russian with English summary].
  • Long, J. A. 1985. The structure and relationships of a new osteolepiform fish from the Late Devonian of Victoria, Australia. Alcheringa, 9, 1-22, figs. 1-14
  • Marshall, J.E.A. & Astin, T.R. 1996. An ecological control on the distribution of the Devonian fish Asterolepis. Newsletters on Stratigraphy, 33:133–144.
  • Min, Z. and Schultze, H.-P. 1997. The oldest sarcopterygian fish. Lethaia, 30, 293-304, figs. 1-9.
  • Min, Z., Yu, X. and Janvier, P. 1999. A primitive fossil fish sheds light on the origin of bony fishes. Nature, 397, 607-610, figs. 1-4.
  • Newman, M. J., den Blaauwen, J.L. 2007b. The synonymy of the Scottish Devonian osteolepid fish Thursius macrolepidotus. Scottish Journal of Geology, 43, 101-106.
  • Orvig, T. 1956, Remarks on the vertebrate fauna of the Lower Upper Devonian of Escuminac Bay.Arkiv for Zool. Band 10 nr 6, p367-426
  • Thomson, K. S. 1964 Gyroptychius (Rhipidistia, Osteolepidae) from the Middle Devonian of Scotland. Annals and Magazine of Natural History, Series 13, 7, 725-732.
  • Thomson, K. S. 1966. Glyptolepis from the Middle Devonian of Scotland. Postilla, 99, 1-10, figs. 1-5, pl. 1, 2.
  • Thomson, K. S. 1967. Notes on the relationships of the rhipidistian fishes and the ancestry of tetrapods. Paleontology, 41, 660-674, figs. 1-3.
  • Thomson, K. S. 1972. New evidence on the evolution of the paired fins of Rhipidistia and the origin of the tetrapod limb, with description of a new genus of Osteolepidae. Postilla, 157, 1-7, figs. 1-5.
  • Traquair, 1875. On the structure and affinities of Tristichopterus alatus (Egerton). Transaction of the Royal Society of Edinburgh, 27, 383-396.
  • Westoll, T. S. 1936. On the structures of the dermal ethmoid shield of Osteolepis. Mag., LXXIII, 157-171, figs. 1-4, pls. I, II.

Tetrapodamorphs