Heterosteus (also known as Heterostius[1][2]) is an extinct genus of heterosteid placoderm of the Middle Devonian known from remains discovered in Europe and Greenland.

[4] Also in later studies it was often misidentified and given names like Ichthyosauroides, Asterolepis asmussi and Chelonichthys asmusii.

[1] Even in recent studies, it is controversial as to whether to use genus name Heterosteus or Heterostius.

[5] The genus differs from Herasmius by having the orbits on slightly longer eyestalk-like projections.

Heterosteus is the type genus for the family Heterosteidae, which belongs to the superfamily Dunkleosteoidea.