Homosteus (also commonly spelled Homostius) 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.

[3][4][5] Notably, Homosteus specimens are the only fish fossils from the Old Red Sandstone to show significant radioactivity.

[1] This species is based on a 15 centimeter-long preorbital plate from the early Eifelian of the Wood Bay formations of Spitzbergen, Norway.

[1] Based on a specimen found in the Emsian epoch-aged layers of the Wood Bay formations of Spitzbergen.

Originally described as "Trionyx latus Kutorga 1837"[1] This species is found in the Eifelian-aged Elm Point Limestone of Manitoba.