Nannopterygius undetermined

Zverkov, Nikolay G. & Jacobs, Megan L., 2021, Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the ‘ inaccessible’ holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution, Zoological Journal of the Linnean Society 191 : -

NANNOPTERYGIUS SP. INDET.

1986 Ophthalmosaurus – Delair, p. 133, fig. 9.

v. 2018 Macropterygius sp. indet. – Moon & Kirton: 117 [pars.].

Referred specimens: OUMNH J 68534 and OUMNH J 12031 , isolated humeri [ Macropterygius sp. indet. in Moon & Kirton (2018)]; OUMNH J 50333 , OUMNH J 48757 , OUMNH J 12450 , isolated basioccipitals; SOTUG 15181, 15198, 15348, 16566 and 16663 [ Ophthalmosaurus in Delair (1986: 130)], partial disarticulated skeleton including vertebra, interclavicle, scapula, both coracoids, humerus, scattered teeth, several phalanges and rib fragments.

Remarks: Here we describe materials from the Kimmeridge Clay Formation that either lack diagnostic features of the species Nannopterygius enthekiodon or differ in some aspects from this species but could be robustly referred to Nannopterygius , partially expanding the knowledge of this taxon. It is possible that these specimens belong to N. enthekiodon , reflecting the intraspecific variation, but their belonging to some other species of Nannopterygius cannot be excluded.

Description

Basioccipital ( Fig 9): Several isolated small basioccipitals from the OUMNH collection are similar to that of N. enthekiodon (see Supporting Information, Table S1). One specimen, OUMNH J. 50333, is clearly deformed by diagenetic compression that resulted in an oval outline of the condyle ( Fig. 9C), similarly to the above-described OUMNH J. 10574/19 and MJML K 1776. In the specimens OUMNH J. 48756 and OUMNH J. 48757, the condyle is nearly as high as wide ( Fig. 9G, K). The posterior notochordal pit is a vertical scar located close to the dorsal edge of the condyle in OUMNH J. 48756 and OUMNH J. 48757, and not observed (probably hidden under the sticker) in OUMNH J. 50333 ( Fig. 9C, G, K). The extracondylar area is reduced and lacks a ventral notch. The peripheral ring of the extracondylar area is separated ventrally by a crest in OUMNH J. 48756 and OUMNH J. 48757, and it is continuous in OUMNH J. 50333 ( Fig. 9B, F, J). The opisthotic and stapedial facets occupy nearly equal height in lateral view ( Fig. 9D, H, L). The exoccipital facets have rounded posterior borders. Medially, these facets are separated by a floor of the foramen magnum that is bilobed anteriorly ( Fig. 9A, E, I). Among ophthalmosaurids, this condition is uniquely shared with Acamptonectes densus ( Fischer et al., 2012) . The anterior surface of the basioccipital is irregularly pitted forming the basisphenoid facet. On this surface, there is a median groove that bears the anterior notochordal pit in its dorsal half, which is marked in OUMNH J. 48756.

Postcranium. The specimen described and figured by Delair (1986) is undoubtedly Nannopterygius with the depicted coracoids ( Delair, 1986: fig. 9), consistent in their dorsal/ventral outline with those of N. enthekiodon . However, this is insufficient overlap for a species identification. Therefore, pending its additional examination, the specimen is here referred to as Nannopterygius sp. indet.

Humerus ( Fig. 8G–K, R–V). Two small humeri, OUMNH J 68534 and OUMNH J 12031 , are here referred to as Nannopterygius sp. indet. Although overall similar to other humeri of Nannopterygius , the specimen OUMNH J 68534 has a marked constriction between the radial and ulnar facets ( Fig. 8U); furthermore, its proximal end is more compressed ( Fig. 8V), similar to that of N. borealis (see description below). Based on the constriction between the radial and ulnar facets, this humerus, along with the humerus OUMNH J 12031 , were previously referred to a dubious taxon ‘ Macropterygius ’ by Moon & Kirton (2018). However, the humerus OUMNH J 12031 lacks that constriction between the distal facets. In contrast, its ulnar facet is slightly dorsoventrally wider than the radial facet ( Fig. 8J). The proximal end of OUMNH J 12031 is more isometric (anteroposterior and dorsoventral widths are close to each other) than those of OUMNH J 68534 and specimens referred to N. enthekiodon . This could be due to some diagenetic distortion, although it could also be a natural condition. Despite the above-described differences, both OUMNH J 68534 and OUMNH J 12031 are most similar to humeri of Nannopterygius among ophthalmosaurids and, therefore, are referred to this taxon in open nomenclature (additionally see discussion on OUMNH J 68534 and Macropterygius ).