Arthrodira is an order of extinct armored, jawed fishes of the class Placodermi that flourished in the Devonian period before their sudden extinction, surviving for about 50 million years and penetrating most marine ecological niches. Arthrodires were the largest and most diverse of all groups of placoderms.
The pelagic selenosteid Amazichthys trinajsticae
Lower jaw plate of Eastmanosteus pustulosus from the Middle Devonian of Wisconsin
Heterosteus ingens from the Middle Devonian of Estonia
Placoderms are members of the class Placodermi, a group of prehistoric fish known from Paleozoic fossils which lived from the Silurian to the end of the Devonian period. While their endoskeletons are mainly cartilaginous, their head and thorax were covered by articulated armoured plates, and the rest of the body was scaled or naked depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first pair of gill arches.
Placoderm
Dunkleosteus, among the first of the vertebrate apex predators, was a giant armoured placoderm predator.
Amazichthys, a pelagic arthrodire from the Middle Famennian of the Late Devonian.
Fin spine of Eczematolepis, from the Middle Devonian of Wisconsin.