Dinichthys was originally described in 1868 by John Newberry on the basis of an incomplete skull roof and mandibles (holotype AMNH 81).

Subsequently, many unrelated large arthrodires were originally classified together within this genus, including species now assigned to Dunkleosteus, Eastmanosteus, and Titanichthys.

However, in the 2010 Carr & Hlavin phylogenetic study, Dunkleosteus and Dinichthys were found to belong to two separate clades.

Carr & Hlavin resurrected the family Dunkleosteidae and placed Dunkleosteus, Eastmanosteus, and a few other genera from Dinichthyidae within it.

The cladogram below shows the phylogeny of Dinichthys:[5] 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