Homosteus

Homosteus
Temporal range: Eifelian-?Givetian
H. milleri
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: †Placodermi
Order: †Arthrodira
Suborder: †Brachythoraci
Family: †Homostiidae
Genus: †Homosteus
Type species
Homosteus formosissimus
Asmuss 1856
Species
  • †H. formosissimus Asmuss 1856
  • †H. arcticus Heintz 1934
  • †H. cf. arcticus Orvig 1969
  • †H. kochi Stensiö & Säve-Söderbergh 1938
  • †H. latus Asmuss 1856
  • †H. manitobensis (Okulitch) 1944
  • †H. milleri Traquair 1888
  • †H. sulcatus (Kutorga) 1837
Synonyms
  • Dinichthys manitobensis Okulitch 1944
  • Homostius sp. Asmuss 1856
  • Homosteus anceps Asmuss 1856
  • Homosteus cataphractus Asmuss 1856
  • Homosteus ponderosus Asmuss 1856
  • Trionyx sulcatus Kutorga 1837
  • Trionyx latus Kutorga 1837

Homosteus is a genus of flattened arthrodire placoderm from the Middle Devonian. Fossils are found primarily in Eifelian-epoch aged strata of Europe, Canada, Greenland, and Estonia.[1] All of the species had comparatively large, flattened heads with, as suggested by the upward opening orbits, upward-pointing eyes. These adaptations suggest that the various species were benthic predators. A study on Titanichthys, in contrast, suggests that species of Homosteus may have been filter-feeders instead.[2]

Homosteus specimens from the Old Red Sandstone of Scotland are known to be significantly radioactive, on the order of 1.2 * 104 gamma/min/g [sic].[3][4][5] Notably, Homosteus specimens are the only fish fossils from the Old Red Sandstone to show significant radioactivity. This suggests that these specimens became radioactive from the animals ingesting radioactive isotopes in life (e.g., through ingesting radioactive sediment),[5] rather than radioactive isotopes being absorbed by the bones during fossilization (as in most cases of radioactive fossils).[6] Individuals of Homosteus from the Old Red Sandstone were chronically exposed to enough radiation that these animals would be expected to suffer negative effects of radiation exposure. However, no specimen of Homosteus shows any sign of bone cancer or other radiation-induced pathologies.[5]

  1. '^ Denison, Robert (1978). Placodermi Volume 2 of Handbook of Paleoichthyology. Stuttgart New York: Gustav Fischer Verlag. p. 71. ISBN 978-0-89574-027-4.
  2. ^ Coatham, Samuel J.; Vinther, Jakob; Rayfield, Emily J.; Klug, Christian (2020). "Was the Devonian placoderm Titanichthys a suspension feeder?". Royal Society Open Science. 7 (5): 200272. doi:10.1098/rsos.200272. PMC 7277245. PMID 32537223.
  3. ^ Bowie, S. H. U.; Atkin, D. (March 1956). "An Unusually Radioactive Fossil Fish from Thurso, Scotland". Nature. 177 (4506): 487–488. doi:10.1038/177487b0.
  4. ^ Diggle, W. R.; Saxon, J. (October 1965). "An Unusually Radioactive Fossil Fish from Thurso, Scotland". Nature. 208 (5008): 400–400. doi:10.1038/208400a0.
  5. ^ a b c Saxon, J. (1979). "The radioactive fossil fishes of the north of Scotland". Caithness Field Club Bulletin. Retrieved 31 December 2022.
  6. ^ Kielan-Jaworowska, Zofia (2013). In pursuit of early mammals. Bloomington: Indiana University Press. ISBN 978-0253008176.