Drepanoistodus iommii Rasmussen & Eriksson & Lindskog 2021, sp. nov.

Drepanoistodus iommii sp. nov.

urn:lsid:zoobank.org:act: 0E2832F5-672E-4FAE-B5A5-CBA5DE1A4824

Fig. 6E–H

partim Drepanoistodus aff. basiovalis – Mellgren & Eriksson 2010: fig. 7m (only).

Drepanoistodus cf. basiovalis – Mellgren et al. 2012: fig. 5e.

Diagnosis

A Drepanoistodus species characterised by a geniculate element with distinct keels on the cusp and upper margin of the base; a straight basal margin; a straight to weakly rounded (convex) anterior margin and cusp which is approximately twice the length of the upper margin of the base.

Etymology

Named in honour of legendary guitarist Tony Iommi, founding member of heavy metal band Black Sabbath.

Material examined Ten geniculate elements including eight from the Lynna section. Holotype, geniculate element (Fig. 6E–F); LO 12479T. Type locality River bank near the mouth of Lynna River, village of Kolchanovo, St. Petersburg region, Russia (60°00′39″ N, 32°33′49″ E). Type stratum

Approximately 10 cm above the local base of the Lynna Formation, sample LY 12-16. Lower part of the Lenodus variabilis Zone.

Description

Cusp reclined and straight with distinct keels developed on the anterior (upper) and posterior (lower) margins. A median, longitudinal carina is developed on both sides of the cusp, but it is especially distinct on the inner side. Base is characterised by a straight or almost straight basal margin and a distinct keel on the upper margin. Whereas this keel is slightly convex, the upper margin below the keel is straight. Anterior margin is usually straight or weakly rounded (convex), but occasionally, it is strongly rounded. Angle A between the cusp and upper margin of the base is ca 30° (mean) with a standard deviation at 4.2 (Fig. 5B), and the mean ratio between length of the free upper margin (b) and the free cusp (c) is 0.54 (standard deviation 0.10).

Remarks

In the PCA plot (Fig. 4), the population of D. iommii sp. nov. is situated in the upper right corner, separated from the D. basiovalis population as well as the other two new species populations described herein. The vectors in the biplot demonstrate that this is mainly due to the straight basal margin, the relatively long upper margin (high b/c values), and the usually straight anterior margin in D. iommii sp. nov., which is in accordance with the characters diagnosed above. The hypothesis that the population of D. iommii sp. nov. is morphologically different from the D. basiovalis population is supported by the PERMANOVA test (Fig. 5A), which shows that the probability that the two populations are the same is exceedingly low (p (same) = 1.00E- 04).

Occurrence

The L. antivariabilis Zone (sample LY12-9) to the L. variabilis Zone (sample LY12-21b). Outside the St. Petersburg region, D. iommii sp. nov. has been recorded from the L. variabilis Zone at the Hällekis quarry in Västergötland, Sweden (Mellgren & Eriksson 2010; referred to as D. aff. basiovalis) and from the L. pseudoplanus Zone or E. suecicus Zone of the island Osmussaar, Estonia (Mellgren et al. 2012; reported as D. cf. basiovalis).