Sandbergeroceras costatum ( d’Archiac & de Verneuil, 1842 )

Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 771, pp. 1-79 : 71-73

Sandbergeroceras costatum ( d’Archiac & de Verneuil, 1842)

Figs 50B , 51A , 53A ; Table 31

Goniatites costatus d’Archiac & de Verneuil, 1842: 340 , pl. 31 fig. 1, 1a.

Triainoceras costatum – Hyatt 1884: 336. — Korn & Klug 2002: 148, text-fig. 137h.

Sandbergeroceras costatum – Schindewolf 1940: 434, pl. 1 figs 4–5, text-fig. 32.

non Triainoceras costatum – Frech 1897: 177 e, fig. 1b, e; 1902: 62, fig. 20c. — Belka et al. 1999: pl. 5 figs 1–2. — Korn & Klug 2002: 148, text-fig. 137d, f.

non Triaenoceras costatum – Drevermann 1903: 85, pl. 5 figs 1–5.

non Sandbergeroceras costatum – Termier & Termier 1950: 54, pl. 150 figs 52–54.

non Pharciceras (Sandbergeroceras) costatum – Petter 1959: 144, pl. 8 fig. 13, 13a, text-fig. 33g, l.

Diagnosis

Species of Sandbergeroceras with discoidal, evolute conch at 30 mm dm (ww /dm ~0.45; uw/ dm ~ 0.40). Whorl profile weakly depressed (ww/ wh ~1.30); venter narrowly rounded. Two moderately deep spiral grooves on the venter. Shell ornament with 30 sigmoidal, sharp ribs on the flanks and coarse growth lines.

Material examined

Neotype (here designated) GERMANY • Rhenish Mountains , Dillenburg; early Frasnian (Red Ironstone); Erbreich Coll.; MB.C.7695 . ( Fig. 50B )

Remarks to the type material

The whereabouts of the original material is not known. The specimen illustrated by d’Archiac & de Verneuil (1842: pl. 36 fig. 1) does not exist in the de Verneuil collection at the University of Lyon, where other original specimens of this work are located (Emmanuel Robert, written comm., April 8 th, 2021). However, the description and illustration by d’Archiac & de Verneuil (1842) allows the species to be characterised ( Fig. 53 ). The only available specimen MB.C.7695 corresponds well with the one illustrated by d’Archiac & de Verneuil (1842), in conch form as well as sculpture and suture line. It can therefore, with little doubt, be considered conspecific. It is herewith proposed as the neotype of the species.

Description

MB.C.7695: incomplete, somewhat distorted specimen of about 42 mm conch diameter in iron-rich limestone ( Fig. 50B ). Although somewhat deformed laterally, it allows the study of conch geometry and ontogenetic development. At 33 mm diameter, the conch is discoidal and subevolute (ww / dm ~ 0.45, uw/ dm ~0.40) with a broad pear-shaped whorl profile (ww /wh ~ 1.30), which is widest in the middle of the flanks. The umbilical edge is rounded; the external side has a rounded keel accompanied by

shallow longitudinal grooves. The interior whorls are poorly preserved and do not allow any study of the ornament. The last one and one-half whorls possess sharp ribs, which initially extend with a concave curve, then straight and finally with a slightly convex curve over the flank. The penultimate whorl shows sharp growth lines with the same course as the ribs.

Only a short portion of the suture line is visible in the ventral area. The external lobe is parallel-sided with a median saddle that reaches about half the height of the lobe. The E 1 lobe is very narrow and very deep ( Fig.51A ).

Remarks

Sandbergeroceras costatum differs from S. tuberculosocostatum in the form of the whorl profile, which is much stouter in S. costatum (ww/ wh ~ 1.30 in comparison to ~ 1.10 in S. tuberculosocostatum ). The whorl profile begins to flatten with a subacute venter already at about 30 mm conch diameter in S. tuberculosocostatum , while the venter is still rounded at this diameter in S. costatum .

The main difference to S. archiaci sp. nov. is that the ventrolateral grooves are less pronounced in S. costatum . The umbilicus is, at a comparable diameter, narrower in S. costatum (ww/ dm ~ 0.40 in S. costatum but ~ 0.50 in S. archiaci sp. nov.).

Figures

Fig. 50. A. Sandbergeroceras archiaci sp. nov., holotype MB.C.3671 (Koch Coll.) from Oberscheld (Anna Mine). B. Sandbergeroceras costatum (d’Archiac & de Verneuil, 1842), neotype MB.C.7695 (Erbreich Coll.) from Dillenburg.C. Sandbergeroceras tuberculosocostatum (Sandberger & Sandberger, 1850), specimen SMF.Mbg.6360 from Oberscheld. Scale bar units = 1 mm.

Fig. 51. A. Sandbergeroceras costatum (d’Archiac & de Verneuil, 1842), suture line of neotype MB.C.7695 from Dillenburg, at ww =15.7 mm, wh= 12.7 mm.B. Sandbergeroceras tuberculosocostatum (Sandberger & Sandberger, 1850), suture line of specimen SMF.Mbg.6360 from Oberscheld, at ww =13.5 mm, wh =15.5 mm. Abbreviations: see Material and methods. Scale bar units = 1 mm.

Fig. 53. Triainoceratidae from the Red Ironstone Formation, all reproduced from d’Archiac & de Verneuil (1842). A. Sandbergeroceras costatum (d’Archiac & de Verneuil, 1842). B. Sandbergeroceras incertum (d’Archiac & de Verneuil, 1842). C. Sandbergeroceras tuberculosum (d’Archiac & de Verneuil, 1842). Scale bar units = 1 mm.

Tables

Table 31. Conch dimensions and ratios of selected specimen ofSandbergeroceras costatum (d’Archiac & de Verneuil, 1842).

Specimen	dm	ww	wh	uw	ah	ww / dm	ww / wh	uw / dm	WER	IZR
MB.C.7695	33.2	15.1	11.7	13.5	7.3	0.45	1.29	0.41	1.64	0.38