Cenoceras rumelangense Weis & Schweigert & Wittische 2023, n. sp.
Creators: name: Weis, Robert
name: Schweigert, GÜnter
name: Wittische, Julian
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Nautilida
Nautilidae
Cenoceras
Cenoceras rumelangense

description: Cenoceras rumelangense n. sp. [Weis & Schweigert]
Figures 5, 6, 7, 8, 9
1995 Cenoceras sp.: Dietl, p. 357, fig. 1.
2005 Cenoceras sp.: Gross, p. 58.
? 2008 Cenoceras gr. obesum: Rulleau, pl. 22, fig. 2 [only specimen EPF Baj74].
2013 Cenoceras sp.: Dietl, p. 20, fig. 24.
? 2016 Metacenoceras sp.: Grulke, p. 139, figs. 1&2.
2021 Cenoceras obesum: Schweigert, p. 9, fig. 14.
Derivation of name: The species is named after the town of Rumelange, a municipality in the southernmost part of Luxembourg that is widely known for its rich fossil findings from Toarcian to Bajocian rocks, including the herein described nautilids.
Holotype: Holotype is specimen MNHNL BM790 (Fig. 5).
Paratypes: 17 specimens from the Humphriesianum Zone of Rumelange (MNHNL: BM232, BM237, BM278, BM280, BM370, BM372, BM383, BM641, BM783, BM784, BM791, BM792, BM793; MEP1; MNM1; Geolor 1 & 2) and one specimen from the Middle Jurassic Ostreenkalk Formation (Humphriesianum Zone) of Gruibingen, Baden-Württemberg (SMNS 62245).
Type locality: Rumelange, abandoned quarry site ʽ Berenskaul-Waisskaul’ on the Luxembourgish–French border (Coordinates 49°27 ′ 12 ʺ N and 6°00 ′ 41 ʺ E; Bintz et al., 1973, p. 159) (Fig. 3).
Type horizon: ‘Marnes sableuses d’Audun-le-Tiche’ (dom4), lower Bajocian, Humphriesianum Zone.
Diagnosis: Giant-sized, narrow-umbilicate species of Cenoceras with strongly inflated subtrapezoidal whorl section, generally higher than wide; longitudinal striation on the flattened venter and on the outer third of the flank.
Description: The holotype (Fig. 5) is a steinkern with a few preserved remnants of the shell. The body-chamber occupies half of the last whorl. The last septa are more closely spaced, indicating that the specimen reached the adult age. The venter is distinctly flat and is ornamented with dense longitudinal striae that are particularly well developed on the body-chamber and which extend on the outer third of the flanks. The section of the body-chamber is markedly subtrapezoidal, compressed (compression index is 0.81 on the body-chamber and 0.77 on the phragmocone); the compression is more marked in younger whorls and less strong on the body-chamber but does not affect the lateral dimensions. The flanks are slightly rounded on the inner third (located towards the umbilicus) and distinctly flattened to slightly concave on the outer two thirds. The flanks are covered with fine falciform striae, and the outer third shows a reticulate ornamentation pattern. The phragmocone shows rather distant septa: the number of septa on the last whorl is n = 10. The lateral lobe is distinctly large and shallow (depth of the lateral lobe = 10 mm), and is followed by an even less profound ventral lobe. The latero-ventral saddle is rather distinctive. Traces of the siphuncle are not visible in this specimen.
Umbilicus: Throughout all ontogenetic stages the overhanging umbilicus remains open, with a well-rounded umbilical edge.
Flanks: Lower part gradually rising from the steep and overhanging umbilicus forming a well-rounded umbilical edge. Middle part of flanks form a trapezoidal section; upper part become slightly concave in the latest part of the adult body-chamber.
Venter: Venter is rounded only in the juvenile stage and soon becomes flattened by developing a prominent ventrolateral edge.
Suture line: On the flank, the suture line forms a single, relatively shallow lateral lobe, with its deepest part located in the outer third of the flank. From the saddle at the ventrolateral edge, it turns towards mid-venter in a right angle without forming an extra ventral lobe.
Ontogeny: Growth pattern lacks principal changes of coiling or other modifications during ontogeny, except the inflated whorl section gradually changing from being rounded in the juvenile stage to subtrapezoidal in the medium and adult stages. In the latest stage, the chambers and suture lines are narrowing thus indicating adult size.
Ornamentation: The almost uncompressed specimen from Swabia (Fig. 9) is the only one with a completely preserved calcitic replacement shell. The adult shell is ornamented with dense longitudinal striae both on the venter and on the outer third of the flank. The aperture does not exhibit any apertural modifications and crosses the venter in a straight way. Due to the shell preservation, the beginning of the body-chamber and the suture lines of the phragmocone cannot be traced.
Measurements and morphometrics: Various measurements and parameters of C. rumelangense specimens are reported in Table 1. We compared the data with measurements and parameters published for two coeval large-sized nautilid taxa: Cenoceras obesum (sensu Rulleau, 2008) and Metacenoceras clausum.
description: Published as part of Weis, Robert, Schweigert, GÜnter & Wittische, Julian, 2023, A new giant nautilid species from the Middle Jurassic of Luxembourg and Southwest Germany, pp. 1-11 in Swiss Journal of Palaeontology (24) (24) 142 (1) on pages 5-6, DOI: 10.1186/s13358-023-00290-6, http://zenodo.org/record/12001012