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

Abstract: 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

The problem of dating the Kuyeda-Klyuchiki section – a unique locality of Permian vertebrates (Perm Region, Russia)

The Kueda-Klyuchiki locality of Permian vertebrates located in the south of the Perm Region in the Kuedinsky District was discovered in 2005 and quickly became known among paleontologists. The locality contains a rich complex of exceptionally preserved plants and vertebrates (fish, amphibians, and reptiles). Their remains are confined to limestones of various textures, which form two bone-bearing beds in the section of the quarry. However, the age of rocks remains a controversial issue. This research aims to analyze and compare various stratigraphic markers and discuss a number of existing stratigraphic inconsistencies in an attempt to arrive at a general conclusion about the age of the locality. According to geological survey data on a scale of 1:200 000, the Buraevo Sequence (Sheshmian Formation, Ufimian Stage) was identified in the territory of the quarry. At the boundary of the Sheshmian and Belebey Formations, a mineralogical “boundary” is observed, which is manifested in a decrease in the proportion of minerals of the epidote group and an increase in the content of black ore minerals. Terrigenous rocks of the Kueda-Klyuchiki section are close to the values of the Sheshmian Formation, in terms of the amount of epidote and black ore minerals in the heavy fraction. The results of the geochemical study indicate that the bitumoids of the Kueda-Klyuchiki and Posad outcrops (Kazanian Stage) developed in different paleogeographic and geomorphological conditions. The bitumoids of the Kazanian outcrop Posad formed through the sapropelic organic matter accumulated in the coastal-marine reducing conditions, while the organic matter of the Kueda-Klyuchiki outcrop formed in the relatively deep-water conditions. The composition of the ichthyological assemblage indicates the Upper Kazanian age of the section. The fish orictocenosis includes Kazanichthys viatkensis, Acropholis kamensis, Acropholis stensioei, Palaeoniscum kasanense, Platysomus biarmicus, Kargalichthys efremovi, Kargalichthys pritokensis, Platysomidae gen. indet., Palaeonisci ordo indet. sp. 1, Palaeonisci ordo indet. sp. 2. Its composition indicates that Kueda-Klyuchiki has higher stratigraphic position than most Upper Kazanian localities, which is confirmed by the absence of terminal Kazanian species. However, the composition of the ichthyofauna in Kueda-Klyuchiki differs significantly from that of the early Kazanian localities, typical of the Kazanichthys golyushermensis ichthycomplex. The orictocomplex of fish from the Kueda-Klyuchiki locality is most similar to the two Upper Kazanian localities – Aksakovo (Pechishchi beds) and Shikhovo-Chirki (Verkhnyi Uslon beds). The complex of amphibians includes temnospondyls (presumably, Melosauridae), discosauriscid (Discosauriscidae gen. ind.) and kotlassiid (Leptoropha sp.) seymouriamorphs, diapsids, and therapsid reptiles. To clarify the age of the Kueda-Klyuchiki outcrop, the results of the mineralogical analysis of the heavy fraction of terrigenous rocks and the geochemical characteristics of the dispersed organic matter from the carbonate-clayey rocks of the section are presented. The results obtained can serve as a starting point for further multidisciplinary research

Feeding convergence among ray-finned fishes: Teeth of the herbivorous actinopterygians from the latest Permian of East European Platform, Russia

© 2020 Instytut Paleobiologii PAN. All rights reserved. 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

Feeding convergence among ray-finned fishes: Teeth of the herbivorous actinopterygians from the latest Permian of East European Platform, Russia

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