Isadia suchonensis Minikh, 1986

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 suchonensis Minikh, 1986

Fig. 2K–M .

Material.—Isolated teeth ( ZPAL V.51/11–13) and 25 unnumbered teeth: 14 maxillary and 11 mandibular from Sokovka outcrop, Vyazniki in Vladimir Region, Russia, late Permian (Upper Vyatkian).

Description.—The teeth are curved in anterior view, with tips directed slightly lingually. A shallow row in the middle of the crown is visible on the labial side in some specimens. It is oriented parallel to the tooth axis. Teeth are small and have interior passage larger than Isadia aristoviensis and it ends close to the tips of the crown. The crown of the collected teeth has 4–7 cusps (in some specimens of this species collected from other outcrops show 3–9 cusps on the crown). The tips of the cusps are not covered by acrodine (in our investigations, the acrodine tips in discussed species are developed and clearly distinct from tooth bases in absence of tubercle microstructure of the external surface). The length of the teeth is 1.16–1.47 mm. Two morphotypes of these teeth were found. One with 4–5 cusps, and second with 6–7 smaller cusps. The mandibular teeth have straight base of the crown with less cusplets than crowns of the maxillary teeth ( Minikh et al. 2015).

Remarks.— Isadia suchonensis Minikh, 1986 (holotype SGU 104 Б/P-2, Mutovino locality) is the type species of this genus. It is distinguished by elongated and narrow teeth on a short maxilla (Minikh and Minikh 1986). All maxillary teeth are morphologically similar to each other. The mandibular teeth differ by width of cusplets. All have wide crown with many small cusps. The teeth from Sokovka outcrop are not as large as in previously known specimens of I. suchonensis . In the holotype of I. suchonensis acrodine is very small but still noticeable. The small size of specimens from Sokovka suggests that it might be a subspecies of I. suchonensis that developed lack of acrodine or this is an effect of ontogeny. Likewise, this could be a preservational artifact. This requires further research.

Stratigraphic and geographic range.—Permian, East European Platform.

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).