Drepanoistodus aff. basiovalis (Sergeeva, 1963)

Fig. 6P–Q

aff. Oistodus basiovalis Sergeeva, 1963: 96, pl. 7 figs. 6–7, text-fig. 3. Drepanoistodus cf. basiovalis (Sergeeva, 1963) – Löfgren 2000a: fig. 4v.

Drepanoistodus aff. basiovalis – Mellgren & Eriksson 2010: fig. 7g –h.

Drepanoistodus basiovalis – Serra et al. 2019: fig. 7k. — Wu et al. 2020: fig. 3ah–ai.

Material examined

Seven geniculate elements including five from the Lynna section .

Remarks

The specimens assigned to Drepanoistodus aff. basiovalis herein share some characters with D. basiovalis, D. iommii sp. nov. and D. stougei, but do not meet the full criteria of any of these species. The most significant character is an extended upper keel anteriorly, which may be angular (see Fig. 6P–Q) or rounded. Cusp is reclined and straight with distinct carinas on both sides of the cusp. Anterior margin varies from almost straight to rounded (convex). The upper anterior corner is angular or weakly rounded. The basal margin is usually slightly convex. The cusp is often nearly twice as long as the upper margin of the base, but it varies considerably (b/c ratio mean = 0.46, standard deviation 0.14). Similarly, angle A is very variable with a mean near 28° and standard deviation at 6.55 (Fig. 5B). Specimens with a rounded anterior edge share similarity with Drepanoistodus stougei Rasmussen, 1991 but are distinguished by the extended upper keel anteriorly, and a more narrow and distinct carina. More material and analyses are needed to assess if this taxon represents a separate species. Thus, for the time being, these specimens are left under open nomenclature.

Occurrence

The L. antivariabilis Zone (sample LY12-9) to the basal part of the L. variabilis Zone (sample LY12- 14). Moreover, it has been recorded from the B. norrlandicus Zone at Gillberga, Sweden (Löfgren 2000a, as D. cf. basiovalis); the L. variabilis Zone at Hällekis, Sweden (Mellgren & Eriksson 2010); and also from the L. pseudoplanus Zone of the Argentine Precordillera (Serra et al. 2019, as D. basiovalis) and Histiodella kristinae Zone of Zhejiang, China (Wu et al. 2020, as D. basiovalis).