Oxyosteus is a genus of trout-sized, highly compressed arthrodire placoderms from the Late Devonian of Europe: The two described species are restricted to the Late Frasnian-aged Kellwasserkalk Fauna of Bad Wildungen, while a median dorsal plate of an unnamed species is known from the Middle Frasnian Holy Cross Mountains of Poland.

Species have, in cross section, an extremely compressed body, a pointed, highly elongated snout, and tremendous orbits.

The genus is distinguished from other members of the family in that the plates are very thin, and the dermal surface is typically covered in small, closely packed tubercles.

[1] Oxyosteus magnus is the larger of the two described species from Bad Wildungen; the skull length of the holotype is 18 cm long.

The plate was found in the Middle Frasnian portion of the Late Devonian strata of the Holy Cross Mountains in Poland.