Hadrosteus is an extinct monospecific genus of large arthrodire placoderm from the Late Frasnian (Late Devonian) Kellwasserkalk facies of Bad Wildungen, Germany.

[1] It had large, double-pronged inferognathals (lower jawbones), and serrated edges along its mandible, strongly suggesting that it was a fish-eating predator.

The head had a triangular snout, and the trunkshield was short, but high, with a median dorsal plate that was broader than wide.

[1] The type species Hadrosteus rapax means "Rapacious Strong-Bone".

The cladogram below shows the phylogeny of Hadrosteus:[2] Coccosteomorphi Rhachiosteus pterygiatus Eastmanosteus calliaspis Eastmanosteus pustulosus Kiangyousteus yohii Golshanichthys asiatica Westralichthys uwagedensis Dunkleosteus raveri Dunkleosteus terrelli Dunkleosteus amblyodoratus Heterosteus ingens Yinosteus major Tapinosteus heintzi Bullerichthys fascidens Kendrickichthys cavernosus Bruntonichthys multidens Dinichthys herzeri Hadrosteus rapax Gorgonichthys clarki Heintzichthys gouldii Pachyosteus bulla Gymnotrachelus hydei Stenosteus angustopectus Brachyosteus dietrichi Melanosteus occitanus Rhinosteus parvulus