Abstract

A new morphotype of multicuspid teeth belonging to the actinopterygian order Eurynotoidiformes and supposedly associated with Isadia opokiensis A. Minich et Andrushkevich, 2017 was found in the terminal deposits of the East European Severodvinian Stage (Maryushkina Sluda-C locality, Vologda Region). The original description of this species was based upon isolated scales obtained from the stratigraphically and geographically adjacent Mutovino locality. Teeth of the I. opokiensis morphotype are robust and are characterized by a powerful buttress and a wide crown bearing numerous (up to eight) spade-shaped cusps with high acrodine caps. Cusp tips form a slightly curved occlusal surface. Labially, these tips bear well defined facets formed by lifetime wear that suggest algal scraping as the predominant feeding mode. Tooth structure in Isadia opokiensis is morphologically transitional between that of I. suchonensis and I. arefievi, suggesting a morphoevolutionary succession. The similar (flat) crown shape in another Isadia species, I. aristoviensis, may have originated convergently by modification of a more primitive morphotype found in Urzhumian eurynotoidids.

中文翻译：

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来自欧洲俄罗斯上二叠纪沉积的一种新的形态的鱼齿阶Eurynotoidiformes（Actinopterygii）

摘要

在东欧Severodvinian期的末期沉积物中发现了一种新的多尖齿形态，属于放线翅目阶Eurynotoidiformes，据推测与Isadia opokiensis A.Minich et Andrushkevich有关（2017年，沃洛格达州，Maryushkina Sluda-C地区）。该物种的原始描述是基于从地层和地理上相邻的Mutovino地区获得的孤立尺度。I. opokiensis的牙齿形态型强壮，特征在于有力的支撑和宽冠，带有多个（最多八个）锹形的尖头，带有高的丙烯醛帽。尖锐的尖端形成一个稍微弯曲的咬合表面。阴唇上，这些尖端具有定义明确的刻面，这些刻面是由终身磨损形成的，这表明藻类刮擦是主要的进食方式。在牙齿结构Isadia opokiensis是形态之间过渡的I. suchonensis和I. arefievi，提示morphoevolutionary继承。在另一个伊萨迪亚物种马兜铃I. aristoviensis中，类似的（扁平）冠状形状可能是通过对在乌尔祖姆人的类古猿中发现的更原始的形态学类型进行修饰而趋同起源的。