Two new species of Dunkleosteus Lehman, 1956, from the Ohio Shale Formation (USA,Famennian) and the Kettle Point Formation (Canada,Upper Devonian), and a cladistic analysis of the Eubrachythoraci (Placodermi,Arthrodira)

Two pachyosteomorph arthrodires are described from the Upper Devonian of North America, Dunkleosteus raveri sp. nov. and Dunkleosteus amblyodoratus sp. nov. (from the Appalachian and the Michigan basins, respectively). Dunkleosteus raveri sp. nov. is found stratigraphically below the only other species within the Ohio Shale Formation (Famennian), and is characterized by the retention of a primitive dermal ornamentation, and shares with Dunkleosteus terrelli ( Newberry, 1873 ) the possession of articular facets on the parasphenoid. Dunkleosteus amblyodoratus sp. nov. (Kettle Point Formation, Upper Devonian), known only from incomplete nuchal, paranuchal, and parasphenoid plates, also retains dermal tuberculation, and is characterized by tapering articular facets on the parasphenoid. The current study reviews three North American species of Dunkleosteus (Du. terrelli, Du. raveri sp. nov. , and Du. amblyodoratus sp. nov. ). Formerly, two subgroups were recognized within the Dinichthyidae, the terrelli and herzeri groups, which are shown here to be members of distinct clades. Dinichthys herzeri Newberry, 1868 (the namesake member of the herzeri group) is now the sole member of the family Dinichthyidae comb. nov. , and is assigned to the Aspinothoracidi sensu Miles & Dennis, 1979 . Heintzichthys Whitley, 1933 and Gorgonichthys Claypole, 1892 (additional members of the herzeri group) were previously placed among the aspinothoracid arthrodires. Likewise, Holdenius holdeni Dunkle & Bungart, 1942 (the final member of the herzeri group) and Hadrosteus rapax Gross, 1932 are now placed within the Aspinothoracidi. The remaining taxa, formerly assigned to the Dinichthyidae (i.e. Dunkleosteus Lehman, 1956 ; Eastmanosteus Obruchev, 1964 ; Golshanichthys Lelièvre, Janvier, & Goujet, 1981 ; and Westralichthys Long, 1987 ), are united within the Dunkleosteidae Stensiö, 1963 . © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 159 , 195–222.