Subphylum Vertebrata Rank Family | Phylum Chordata Class Placodermi | |
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Selenosteidae is a 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 (The Cleveland Shales), Eastern Europe (Holy Cross Mountains, Poland, and the Kellwasserkalk fauna of Bad Wildungen), and Northeastern Africa (the Anti-Atlas Mountains, Morocco).
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
Below is a cladogram from Rücklin (2011):
Denison (1978) separated Selenosteidae into two informal groups, the "American" genera (i.e., those taxa from the Upper Famennian Cleveland Shales, such as Selenosteus and Gymnotrachelus), and the "European" genera (i.e., those taxa from the Upper Frasnian Kellwasserkalk facies of Germany, and later, Morocco, like Rhinosteus and Microsteus). 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 (2011), on the other hand, places Pachyosteus as the most basal selenosteid, then groups the American genera (with Selenosteus grouped as the sister taxon of Gymnotrachelus and Stenosteus) as being the sister group of the remaining European/Kellwasserkalk genera, plus Draconichthys.
Some experts imply that Selenosteidae is paraphyletic, as the genus Rhinosteus is often depicted in arthrodire cladograms as being the sister taxon to the Dinichthyloidea taxa Dinichthys (ne "Dinichthyidae"), Gorgonichthys, Heintzichthys, and Hadrosteidae.