Dunkleosteidae is an extinct family of arthrodire placoderms. The gigantic apex predator Dunkleosteus terrelli is the best known member of this group. While they were previously thought to be close relatives of the genus Dinichthys (when they were not synonymized as each other) and grouped together in the family Dinichthyidae, more recent studies have shown that the two taxa represent two very distinct clades within Arthrodira. The reappraisal of Kiangyousteus lead to a restructuring of the family, with the inclusions of the benthic, aberrant Heterosteus (and the other members of Heterosteidae) as the sister taxon of Dunkleosteus, and the Late Emsian Xiangshuiosteus as the sister taxon of Eastmanosteus calliaspis (with the direct implication that E. calliaspis does not belong in Eastmaneos