Selenosteidae
Selenosteidae is an extinct family of small to large-sized arthrodire placoderms from the Late Devonian. With the exception of the Chinese Phymosteus, selenosteids lived in shallow seas in what is now Eastern North America, Eastern Europe, and Northeastern Africa.
Selenosteids have, in cross section, a rounded body, a blunt snout, and tremendous orbits. The lower jaws were slender, the inferognathals usually either being finely serrated, or adapted for crushing, though, in Draconichthys, the inferognathals had long prongs for seizing prey. The rostrum is very small.
Taxonomy
Selenosteidae is a member of the clade Aspinothoracidi, which belongs to the clade Pachyosteomorphi, one of the two major clades within Eubrachythoraci. Gorgonichthys is closely related to the family Selenosteidae, and could possibly be included in the family. The cladogram below shows the placement of Selenosteidae within Eubrachythoraci:Below is a more detailed cladogram of Selenosteidae, from Rücklin :
Denison separated Selenosteidae into two informal groups, the "American" genera, and the "European" genera. Denison notes that the differences between the two groups, such as how the American genera tend to have slightly smaller orbits, and slightly longer cheeks, may suggest the similarities between them are due to parallel evolution.
Rücklin, on the other hand, places Pachyosteus as the most basal selenosteid, then groups the American genera as being the sister group of the remaining European/Kellwasserkalk genera, plus Draconichthys.