Isadia arefievi Minikh, 2015

Pindakiewicz, Maciej, Tałanda, Mateusz, Sulej, Tomasz, Niedźwiedzki, Grzegorz, Sennikov, Andrey G., Bakaev, Alexandr S., Bulanov, Valeriy V., Golubev, Valeriy K. & Minikh, Alla V., 2020, Feeding convergence among ray-finned fishes: Teeth of the herbivorous actinopterygians from the latest Permian of East European Platform, Russia, Acta Palaeontologica Polonica 65 (1), pp. 71-79 : 74

Isadia arefievi Minikh, 2015

Fig. 2J .

Material.—Isolated tooth ( ZPAL V.51/10) and two unnumbered mandibular teeth from Sokovka outcrop, Vyazniki in Vladimir Region, Russia, late Permian (Upper Vyatkian).

Description.—The base of the crown is labio-lingually curved, short and thick. These are characters unique for Isadia arefievi teeth ( Minikh et al. 2015). In the collected teeth the whole crown is very wide and has three cusps (the cusp number of I. arefievi range up to 5, what it seen on specimens from Eleonora locality; see Minikh et al. 2015). The middle cusp is especially wide, making crown shovelshaped. Flat crown is lightly labiolingually curved. The two outer cusplets are very small, thin, and occur on different heights of the tooth. The distal half of the crown is made of acrodine. Width of the crown is between 1.2– 2 mm, teeth are smaller than in Isadia aristoviensis . The length is unknown because collected specimens are not well preserved. They represent mandibular teeth according to the number of cusplets in this species ( Minikh et al. 2015).

Remarks.—The teeth of Isadia arefievi are rare in material from Sokovka. The same morphotype was found only in Vologda Region, Russia, Eleonora site (Salavyoro Formation) and Nizhny Novgorog Region, Russia, Lagernyi Ovrag-3 (Obnora Formation), dated as lower part of the uppermost Permian by ichthyozone Mutovinia sennikovi – Gnathorhiza otschevi ( Minikh et al. 2015). This species of Isadia could have only one row of teeth, forming a tool for scrapping algae. Enlargement of the medium cusp suggests an adaptation to reduce pressure for each tooth while scrapping algae, creating a large abrasive surface. The same trend might be seen in durophagous hybodont teeth ( Ginter 2012). Lack of wide, triangular labial roots of the base is caused probably by some taphonomic factors. The teeth described here suggest that I. arefievi survived to the terminal part of the late Permian in East European Platform.

Stratigraphic and geographic range.—Terminal late Permian of the Moscow Syneclise and southwestern Mezen Syneclise; Russia.

Figures

Fig. 2. The isolated teeth of actinopterygian fish Isadia from the Sokovka outcrop, Vyazniki, Russia, late Permian (Upper Vyatkian). A–D. Isadia aristoviensis Minikh, 1990, mandibulary teeth. A. ZPAL V.51/1, lingual view. B. ZPAL V.51/2, labial view. C. ZPAL V.51/3, lingual view. D. ZPAL V.51/4, labial view. E–I. Isadia aristoviensis Minikh, 1990, maxillary teeth. E. ZPAL V.51/6, lingual view. F. ZPAL V.51/7, labial view. G. ZPAL V.51/5, lingual view. H. ZPAL V.51/8, lingual view. I. ZPAL V.51/9, labial view. J. Isadia arefievi Minikh, 2015, ZPAL V.51/10, mandibular tooth,?lingual view. K, L. Isadia suchonensis Minikh, 1986, mandibular teeth. K. ZPAL V.51/11, lingual (K1) and lateral (K2) views. L. ZPAL V.51/12, labial view. M. Isadia suchonensis Minikh, 1986, ZPAL V.51/13, maxillary teeth,?labial view. Scale bars 1 mm (A–I), 0.5 mm (J, K, M), 0.2 mm (L).