Paucitornoceras paucistriatum (d’Archiac & de Verneuil, 1842) Korn & Bockwinkel, 2022

Korn, Dieter & Bockwinkel, Jürgen, 2022, The tornoceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 806, pp. 32-51 : 47-48

Paucitornoceras paucistriatum (d’Archiac & de Verneuil, 1842) gen. et comb. nov.

Fig. 9 ; Table 5

Goniatites paucistriatus d`Archiac & de Verneuil, 1842: 339, pl. 25 fig. 8.

Tornoceras paucistriatum – Wedekind 1918: 137, pl. 16 fig.11, text-fig. 42a.

Tornoceras (Aulatornoceras) paucistriatum – Grüneberg 1925: 68, pl. 1 figs 4–6.

non Aulatornoceras paucistriatum – House & Kirchgasser 2008: 178, pl. 32 figs 2–13, text-fig. 60d–f.

Diagnosis

Paucitornoceras gen. nov. reaching about 25 mm conch diameter. Thinly discoidal and subinvolute adult stage (ww/dm ~ 0.40; uw/dm <0.30 at 15 mm dm); whorl profile circular (ww/wh ~ 1.00 at 15 mm dm); whorl expansion rate low (WER ~ 1.70). Flanks convex, umbilical margin continuously rounded. With deep ventrolateral groove. Ornament with sharp ribs that become significantly weaker in the adult stage, internal shell thickenings.

Type material

Lectotype (designated here) GERMANY • Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); designated here; Lyon, de Verneuil Collection.

Additional material

GERMANY • Rhenish Mountains, Oberscheld ; late Givetian (Red Ironstone); illustrated in Fig. 9 ; Koch Coll.; MB.C.30414 .

Description

Lectotype

The original specimen in the de Verneuil Collection (Lyon) has nearly 10 mm diameter and is embedded in dark-red limestone with other ammonoids and an orthoconic cephalopod. Unfortunately, it is a rather poorly preserved specimen that would require preparation from the other side to get a better view.

Specimen MB.C.30414

Specimen MB.C.30414 is a 14 mm conch diameter specimen in pink limestone (probably Adorf Limestone). It is much better preserved than the lectotype. Only the last whorl is visible ( Fig. 9 ); it has an almost circular whorl profile with convex flanks separated from the convex venter by a prominent ventrolateral groove, which is more strongly developed on the internal mould. The ornament consists of fine but very sharp ribs running straight across the flank and curving forward to form a prominent ventrolateral projection. Fine growth lines are visible between the ribs. The internal mould shows deep, broad constrictions running parallel to the ribs and forming a semicircular ventral sinus.

Remarks

The original material is preserved in De Verneuil’s collection, which is only partially preserved in Lyon (Emmanuel Robert, pers. comm. 7 Apr. 2021). D’Archiac & de Verneuil (1842: 339) stated that the species is common at Adorf and Oberscheld, of which the latter is the origin of the lectotype. The additional specimen MB.C.30414 described here agrees well in morphology and ornamentation with the lectotype as does the specimen illustrated by Wedekind (1918: pl. 16 fig.11), although that specimen shows the transition to the adult stage with clearly weakened sculpture.

Paucitornoceras paucistriatum differs from P. rhysum in the much wider umbilicus. The specimens described and illustrated by House & Kirchgasser (2008) and placed with ‘ Aulatornoceras paucistriatum ’ are also more closely umbilicate; at the same conch diameter of about 13 mm, this material has a uw/ dm ratio of about 0.20 (uw/dm ~ 0.30 in P. paucistriatum ). The material from New York is possibly a new species.

Figures

Fig. 9. Paucitornoceras paucistriatum (d’Archiac & de Verneuil, 1842); MB.C.30414 (Koch Coll.) from Oberscheld. Scale bar units = 1 mm.

Tables

Table 5. Conch dimensions and ratios of specimen MB.C.30414 of Paucitornoceras paucistriatum gen. et comb. nov. (d’Archiac & de Verneuil, 1842).

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZR
MB.C.30414	13.8	5.7	5.7	4.0	3.2	0.41	1.00	0.29	1.69	0.44