Placodermi is a class of armoured prehistoric fish, known from fossils, which lived from the Silurian to the end of the Devonian period. 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 of their gill arches.
Dunkleosteus is an extinct genus of large arthrodire ("jointed-neck") fish that existed during the Late Devonian period, about 382–358 million years ago. It was a pelagic fish inhabiting open waters, and one of the first apex predators of any ecosystem.
Groenlandaspis is an extinct genus of arthrodire from the Late Devonian. Fossils of the different species are found in late Devonian strata in all continents except eastern Asia. The generic name commemorates the fact that the first specimens of the type species were found in Greenland.
Coccosteus is an extinct genus of arthrodire placoderm from the Devonian period. Its fossils have been found throughout Europe and North America. The majority of these have been found in freshwater sediments, though such a large range suggests that they may have been able to enter saltwater. It was a small placoderm, with Coccosteus cuspidatus measuring 29.6–43.9 cm (11.7–17.3 in) long.
Dinichthys is an extinct monospecific genus of large marine arthrodire placoderm from the Late Devonian measuring around 3 metres (9.8 ft) long. Fossils were recovered from the Ohio Shale Formation along the Olentangy River in Delaware County, Ohio.
Dunkleosteidae is an extinct family of arthrodire placoderms that lived during the Devonian period. The gigantic apex predator Dunkleosteus terrelli is the best known member of this group.
Holonema is an extinct genus of relatively large, barrel-shaped arthrodire placoderms that were found in oceans throughout the world from the Mid to Late Devonian, when the last species perished in the Frasnian-Fammian extinction event. Most species of the genus are known from fragments of their armor, but the Gogo Reef species, H. westolli, is known from whole, articulated specimens.
Gorgonichthys is extinct monospecific genus of large arthrodire placoderm. Fossils are found in the Upper Famennian Cleveland Shales of Late Devonian in Ohio. The type species is Gorgonichthys clarki.
Holdenius is an extinct genus of arthrodire placoderm fish which lived during the Late Devonian period.
Plourdosteus is an extinct genus of placoderm arthrodire which was relatively widespread in Euramerica during the Givetian to Frasnian ages of the Devonian. It was a small placoderm, with P. canadensis measuring 37.5–51.4 cm (14.8–20.2 in) long.
Hadrosteidae is a family of arthrodire placoderms from the Late Devonian. It was originally erected for the late Frasnian Hadrosteus, from the Kellwasserkalk facies. Later, the family was subjectively subsumed into Dinichthyidae due to Hadrosteus' anatomical similarities with Dunkleosteus and Dinichthys. In 1967, Obruchev placed the enigmatic arthrodire incertae sedisDiplognathus, from the Eastern American Famennian, within Hadrosteidae, on the basis of how the two genera have similar denticle ("teeth") patterns of the inferognathals, though, Denison (1978) contests this placement. With the redefining of Dinichthyidae as a monotypic family for Dinichthys, and only a few other genera placed within Dunkleosteidae, Hadrosteidae is now seen as a valid family again.
Stenosteus is an extinct monospecific genus of medium-sized selenosteid arthrodire placoderms of the Late Devonian period known from the Upper Famennian Cleveland Shale of Ohio. Estimated skull lengths range from 6 to 9 centimeters Most fossils of Stenosteus have been scraps of armor and portions of tooth-plates suggestive of Selenosteus. In 1996, enough material of a new species, S. angustopectus, was recovered to allow a reconstruction of armor that resembles that of Selenosteus.
Gymnotrachelus is an extinct monospecific genus of large selenosteid arthrodire placoderm of the Late Devonian known from the Late Famennian Cleveland Shale of Ohio. The type species Gymnotrachelus hydei was originally reconstructed as physically resembling Selenosteus, with slightly smaller orbits. Later specimens led to a reappraisal, and now G. hydei is thought to have a more gar-like or barracuda-like build.
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. 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.
Homostiidae is a family of flattened arthrodire placoderms from the Early to Middle Devonian. Fossils appear in various strata in Europe, Russia, Morocco, Australia, Canada and Greenland.
Heterosteus is an extinct genus of heterosteid placoderm of the Middle Devonian known from remains discovered in Europe and Greenland. According to Denison, 1978, Heterosteus might have been planktivorous, along with Homosteus, and Titanichthys.
Africanaspis is an extinct genus of groenlandaspidid placoderm known from two species, Africanaspis doryssa, named in 1997 from fossils discovered in South Africa and Africanaspis edmountaini, named from fossils described from South Africa during 2017. A. edmountaini is only known from juvenile specimens. Both species are known from the Witpoort Formation. A. doryssa is estimated to have been 23–24.5 cm (9.1–9.6 in) long.
Millerosteus is an extinct genus of coccosteid arthrodire placoderm from the Early Givetian stage of the Middle Devonian period. Fossils are found in the Orkneys and Caithness, Scotland. It was a small placoderm with an body length of 14 cm (5.5 in). Millerosteus is one of the few arthrodires known from specimens preserving the entire skeleton.
Watsonosteus is an extinct genus of coccosteid arthrodire placoderm from the Late Givetian stage of the Middle Devonian period. Fossils are found in the Orkney Islands, Scotland. It was a small placoderm with an total body length of 57 cm (22 in), with the largest individuals reaching lengths of 1 m (39 in). It is one of the few arthrodires for which complete body fossils are known.
Amazichthys is an extinct genus of selenosteid arthrodire from the Middle Famennian of the Late Devonian of the Anti-Atlas Mountains of Morocco. It contains a single species, Amazichthys trinajsticae. It is one of a few example of placoderm known from whole body shape, including cartilaginous axial and fin elements.
