Ganoin

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Fossil of a primitive ray-finned fish with ganoid scales. Typically, the scales of these "ganoids" are very well preserved, while in the geologically younger representatives without ganoid scales it is often not or only poorly passed on.

Ganoin ( Gr . Γάνος , gános , "shine", "jewelry", "enamel") is an enamel- like substance that coats the scales of "primitive" fish from the large group of ray fins (Actinopterygii) with an iridescent shine . The corresponding scales are known as ganoid scales .

education

The osteoblasts in the dermis (dermis, corium) sequentially deposit numerous thin layers of ganoin, which ultimately form the thick layer of enamel in the layered structure of the scale. Ganoin differs from dentin (dentin) in the absence of tooth tubules (dentinal tubules).

Tribal historical aspects

Species with the typical rhomboid ganoid scales were widespread among Paleozoic and Mesozoic ray fins . These species are grouped under the names " Ganoid fish " or " Schmelzschupper ". However, they do not form a closed community of descent ( monophylum ) and thus not a taxon that is valid in the modern system . In the further course of the tribal history of the ray fins, in the later Mesozoic and Cenozoic , forms increasingly prevailed in which the ganoin layer of the scales was or is reduced. Ganoid scales are only found in about 44 species today, which are assigned to the "primitive" groups of bone organoids (holostei, bone pike and close relatives), cartilaginous organoids (chondrostei, sturgeon and closer relatives) and pike fish (cladistia). In the elasmoid scales of the real bony fish (Teleostei), the phylogenetically most progressive and by far the most species-rich line of the ray fins, the ganoin coating (as well as the dentin and cosmin layer) is completely reduced, so that they only develop the thin scale base made of bone-like isopedin .

supporting documents

  • Ulrich Lehmann: Paleontological Dictionary . 4th edition. Enke Verlag , Stuttgart, 1996. Page 93

Individual evidence

  1. ↑ Erwin J. Hentschel and Günther H. Wagner: Zoological dictionary , 6th edition. Gustav Fischer Verlag , Jena, 1996. Page 264.
  2. ↑ Peter Bartsch: Actinopterygii, Strahl (s) flosser . In: Wilfried Westheide, Reinhard Rieger (Ed.): Special Zoology. Part 2: vertebrates or skulls . Spectrum Academic Publishing House , 2004. Page 226.
  3. ↑ Harald Schliemann: Integument and appendage organs . In: Wilfried Westheide, Reinhard Rieger (Ed.): Special Zoology. Part 2: vertebrates or skulls . Spektrum Akademischer Verlag, 2004. page 22.