Devonosteus is an extinct genus of prehistoric marine lobe-finned fish known from the Late Devonian. It contains a single species, D. proteus from the late Frasnian of Wildungen, Germany. It has sometimes been considered a lungfish of the family Holodontidae, but this remains uncertain as the original specimen may be lost. Alternatively, it may be a tristichopterid, a type of basal tetrapodomorph.