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A unique functional adaptation to herbivory within early ray-finned fishes is exemplified by the late Permian actinopterygians within the family Eurynotoidiidae with policuspid teeth strongly modified with respect to the primitive actinopterygian conditions. Here we report additional finds of multidenticulated teeth from the fluvial latest Permian deposits of Russia. The teeth belong to the members of endemic Eurynotoidiidae and show rather high morphological diversity. We confirm that the Russian forms are the earliest known ray-finned fishes with substantial modifications of teeth adapted to the processing of food. These finds confirm some previous suggestions that the adaptation to herbivory first developed in freshwater fishes, not marine. We found very similar dental adaptations in some groups of Recent freshwater teleosts, especially in characiforms and cichlids. It suggests that sympatric species of Permian Eurynotoidiidae explored various herbivorous niches like modern fish in East African lakes. Apparently, this first pulse of adaptive radiation in ray-finned fishes was probably caused by diversification of Permian aquatic vertebrate community. [ABSTRACT FROM AUTHOR]