''Angarichthys hyperboreus'' is an extinct

homostiid 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. Many homostiids have " toothless" jaws, and large sizes ...

arthrodire Arthrodira (Greek for "jointed neck") 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 e ...

placoderm from the Middle Devonian (either upper

Eifelian The Eifelian is the first of two faunal stages in the Middle Devonian Epoch. It lasted from 393.3 ± 1.2 million years ago to 387.7 ± 0.8 million years ago. It was preceded by the Emsian Stage and followed by the Givetian Stage. North American ...

or lower

Givetian The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian Stage. It is named after the town of Givet in ...

) of

Siberia Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part o ...

. It is known from an infragnathal plate, an intero-lateral plate, and a marginal plate found from the Middle Devonian strata of the Tynep Series formation, in the

Bakhta River The Bakhta () is a river in Krasnoyarsk Krai, Russia. It is a right hand tributary of the Yenisey. The Bakhta is long, and the area of its basin is . The lower reaches of the river are navigable. Course The Bakhta has its source in the Tungusk ...

basin,

Tunguska Plateau The Tunguska Plateau ( rus, Тунгусское плато) is a mountain plateau in Krasnoyarsk Krai, Siberia, Russia. It is a part of the Central Siberian Plateau. The plateau is located in largely uninhabited area, the village of Noginsk wa ...

. ''A. hyperboreus'' differs from ''Homosteus'' in that the former's marginal plate has a ridge where the central plate would have overlapped it, and in the infragnathal, which is curved sigmoidally, and bears at least seven tooth-like prongs nearer to the functional anterior end (the plate, which is fragmentary, suggests that the intact plate would have born several more). The living animal would have been fairly large, as the head shield is estimated to be at least 40 centimeters long.

References

{{Taxonbar, from=Q16974264 Homostiidae Fossils of Russia Placoderms of Asia