The Squamation Morphology and Stratigraphic Distribution of Isadia arefievi A. Minich (Actinopterygii, Eurynotoidiformes)

A new morphotype of the ray-finned fish scales of the order Eurynotoidiformes (Actinopterygii) is reported from the upper Permian of Eastern Europe and assigned to the species Isadia arefievi A. Minich, 2015, which was initially described based on isolated teeth. Scales of the new morphotype are found in five localities of the Upper Vyatkian Substage, including the uppermost Permian beds of the Zhukovian Regional Stage, characterized by the Vyazniki Tetrapod Assemblage (Archosaurus rossicus Tetrapod Assemblage Zone). The scales of I. arefievi are closely similar to those of I. opokiensis A. Minich et Andrushkevich, 2017, that confirms the hypothesis on both species belong to one phylogenetic lineage (I. opokiensis–I. arefievi). The new finds of I. arefievi indicate a wide distribution of herbivorous fishes with a scraping feeding mode in Vyatkian aquatic vertebrate assemblages.