Homosteus

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. 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.

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]. 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), rather than radioactive isotopes being absorbed by the bones during fossilization (as in most cases of radioactive fossils). 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.