Early/Mid Silurian – Late Devonian | image = DunkleosteusSannoble.JPG | image_width = 250px | image_caption = Dunkleosteus Skull at Sam Noble Museum | regnum = Animalia | phylum = Chordata | subphylum = Vertebrata | infraphylum = Gnathostomata | classis = Placodermi | classis_authority = McCoy, 1848 | subdivision_ranks = Orders | subdivision = Antiarchi † Arthrodira † Brindabellaspida † Petalichthyida † Phyllolepida † Ptyctodontida † Rhenanida † Ac… (More on Placodermi)