Tornoceras typus (Sandberger & Sandberger, 1851)

Korn, Dieter & Bockwinkel, Jürgen, 2022, The tornoceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 806, pp. 32-51 : 36-38

Tornoceras typus (Sandberger & Sandberger, 1851)

Fig. 4 ; Table 1

Goniatites retrorsus var. typus Sandberger & Sandberger, 1851: 109 , pl. 10 fig. 14.

Tornoceras simplex Mut. typus – Holzapfel 1895: 98, text-fig. 6, pl. 6 fig. 11, pl. 7 fig. 9. Tornoceras typus – Korn 2021b: 149, text-figs 2–5, 6a.

Tornoceras typum – Becker 1993: 182, pl. 3 figs 1–2. — Korn & Klug 2002: 156, text-fig. 139.

? Goniatites retrorsus var. typus – Sandberger & Sandberger 1851: pl. 10a figs 3–6, 10–11.

? Tornoceras simplex – Foord & Crick 1897: 69, 107, text-figs 25d–f, 48.

? Tornoceras simplex mut. ovata – Frech 1902b: 47, pl. 3 fig. 21.

non Tornoceras typum – Becker 1993: 182, pl. 3 figs 3–4, text-fig. 68a. — Becker et al. 2000: pl. 2 figs 7–8. — Korn & Klug 2002: 156, text-fig. 143a–c.

non Tornoceras simplex – Frech 1902: 47, pl. 5 fig. 8. — Wedekind 1918: 135, pl. 16 fig. 12, textfig. 40a.

Diagnosis

Tornoceras reaching about 90 mm conch diameter. Thickly pachyconic, subevolute early juvenile stage (ww/dm ~ 0.80; uw/dm ~ 0.35 at 2 mm dm), thickly discoidal and involute subadult stage (ww/ dm ~ 0.58; uw/dm ~ 0.08 at 10 mm dm), thinly discoidal and involute adult stage (ww/dm ~ 0.42; umbilicus closed at 30 mm dm). Whorl profile as wide as high in the subadult stage (ww/wh ~ 1.00 at 10 mm dm) and strongly compressed in the adult stage (ww/wh ~ 0.75 at 30 mm dm); whorl expansion rate very high in the subadult and adult stage (WER = 2.30-2.45). Flanks convex, convergent, umbilical margin continuously rounded. Without any ventrolateral grooves. Suture line with broadly rounded, asymmetric adventive lobe and high ventrolateral saddle.

Type material

Lectotype GERMANY • Rhenish Mountains, Oberscheld ; probably middle Frasnian (Adorf Limestone); designated by Becker (1993); figured by Sandberger & Sandberger (1850 –1856: pl. 10 fig. 14), Becker (1993: pl. 3 figs 1–3) and Korn (2021b: text-fig. 2), re-illustrated here in Fig. 4 ; specimen 53a; Wiesbaden Museum .

Additional material examined

GERMANY • 1 spec.; Rhenish Mountains , Oberscheld; middle Frasnian (Adorf Limestone); Erbreich Coll.; MB.C.4466 • 1 spec.; Rhenish Mountains , Oberscheld; middle Frasnian (Adorf Limestone); Koch Coll.; MB.C.30409 • 1 spec.; Rhenish Mountains , Dillenburg , Eiserne Hand (Grube Friedrich); middle Frasnian (Adorf Limestone); MB.C.30410 .

Description

Lectotype 53a (Wiesbaden Museum)

Fairly well-preserved specimen with 46 mm conch diameter in red limestone; it is largely chambered and the last half volution belongs to the body chamber ( Fig. 4 ). It is a thinly discoidal conch (ww/ dm = 0.40) with a closed umbilicus. The body chamber is obviously slightly distorted, resulting in a stronger convergence of the flanks (as shown in the original illustration by Sandberger & Sandberger 1850 –1856). Parts of the specimen are covered by shell material, which, however, is not well preserved and does not allow a detailed examination of the ornamentation. The suture line has a small, V-shaped outer lobe and a broadly rounded ventrolateral saddle. The adventitious lobe is twice as deep as the outer lobe and as deep as it is wide; it is broadly rounded and slightly asymmetric.

Remarks

The species has been discussed several times in the literature. A detailed revision and discussion was carried out by Korn (2021b); in this paper both the taxonomic problems and the conch morphology as well as the ontogenetic development are presented on the basis of further material from the Rhenish Mountains.

Figures

Fig. 4. Tornoceras typus (Sandberger & Sandberger, 1851), reproduction of the lectotype illustrations by Sandberger & Sandberger (1850–1856, pl. 10 fig. 14) and the photography by M.R. House in Becker (1993, pl. 3 figs 1–2). Scale bar units = 1 mm.

Tables

Table 1. Conch dimensions and ratios of Tornoceras typus (Sandberger & Sandberger, 1851), lectotype (Wiesbaden 53a).

Specimen	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZR
Wiesbaden 53a	46.0	18.3	29.7	0.0	15.2	0.40	0.62	0.00	2.23	0.49