Diplognathus

{{Short description|Extinct genus of fishes}}

{{Italic title}}

{{Taxobox

| name = Diplognathus

| fossil_range = Late Famennian

| image = Diplognathus.jpg

| image_caption = Reconstructed as hadrosteids

| regnum = Animalia

| phylum = Chordata

| classis = Placodermi

| ordo = Arthrodira

| subordo = Brachythoraci

| infraordo = Coccosteina

| superfamilia = Dinichthyloidea

| familia = ?Hadrosteidae

| genus = Diplognathus

| genus_authority = Newberry, 1878

| type_species = Diplognathus mirabilis

| type_species_authority = Newberry, 1878

| subdivision_ranks = Species

| subdivision =

• D. mirabilis Newberry, 1878
• D. larfargei Carr, 2005

}}

Diplognathus is a genus of arthrodire placoderm from the Late Famennian Cleveland Shale of Late Devonian Ohio, known only from incomplete fragments of jaws and skulls.{{cite book|last=Denison|first=Robert|title=Placodermi Volume 2 of Handbook of Paleoichthyology|year=1978|publisher=Gustav Fischer Verlag|location=Stuttgart New York|isbn=978-0-89574-027-4|pages=105}} What fragments are known suggest that the living animals were large-eyed piscivores with weak, but widely gaping jaws. D. mirabilis is thought to be fairly large, with infragnathals up to 45 centimeters in length. The second species, D. larfargei, was much smaller, with inferognathals averaging about 4 centimeters in length.{{cite journal|last=CARR|first=ROBERT K.|author2=GARY L. JACKSON|title=Diplognathus lafargei sp. nov . From the Antrim Shale (Upper Devonian) of the Michigan Basin, Michigan, U.S.A. |journal=Revista Brasileira de Paleontologia|year=2005|volume=8|issue=2|pages=019–116 (113)|url=http://www.sbpbrasil.org/revista/edicoes/8_2/8(2)carr.pdf|doi=10.4072/rbp.2005.2.03|doi-access=free}}

File:Diplognathus mirabilisDB24.jpg of D. mirabilis]]

In 1967, Obruchev placed this genus within Hadrosteidae, on the basis of how the two genera have similar denticle ("teeth") patterns of the inferognathals, though Denison (1978) contested this placement, preferring to leave the taxon as Arthrodira incertae sedis.