Tornoceras frechi Wedekind, 1918

Korn, Dieter & Bockwinkel, Jürgen, 2022, The tornoceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 806, pp. 32-51 : 38-40

Tornoceras frechi Wedekind, 1918

Fig. 5 ; Table 2

Tornoceras Frechi Wedekind, 1918: 136 , pl. 16 fig. 9, text-fig. 41.

Phoenixites frechi – Becker 1993: 198, pl. 6 figs 4–5, text-fig. 73b.

Tornoceras frechi – Korn 2021a: 292, text-figs 2–4, 6a.

Ammonites retrorsus – Beyrich 1837: 30, pl. 1 figs 10–11.

non Tornoceras (Tornoceras) frechi – Petter 1959: 195. non Tornoceras (Tornoceras) frechi frechi – Buggisch & Clausen 1972: 143, pls 1–2, 5. non Tornoceras frechi – Bensaïd 1974: 118, pl. 5 figs 4, 4a. — Makowski 1991: 246, text-fig. 2. non Phoenixites frechi – Becker 1993: 198, pl. 5 figs 12–17, pl. 6 figs 1–3, text-fig. 73a, c, g–i. — Belka et al. 1999: pl. 5 figs 3–4. — Becker et al., 2000: pl. 3 figs 5–6. — Korn & Klug 2002: 160, text- fig. 146f, i. — Niechwedowicz & Trammer 2007: 66, text-fig. 3a–d.

Diagnosis

Tornoceras reaching about 50 mm conch diameter. Thickly pachyconic, subinvolute early juvenile stage (ww/dm ~ 0.75; uw/dm ~ 0.28 at 2 mm dm), thickly discoidal and involute subadult stage (ww/dm ~ 0.45; uw/dm ~ 0.05 at 10 mm dm), thinly discoidal and involute adult stage (ww/dm ~ 0.35; umbilicus closed at 30 mm dm). Whorl profile weakly compressed in the subadult stage (ww/wh ~ 0.75 at 10 mm dm) and more strongly compressed in the adult stage (ww/wh ~ 0.65 at 30 mm dm); whorl expansion rate very high in the subadult and adult stage (WER = 2.25–2.40). Flanks weakly flattened, converging, umbilical margin continuously rounded. Without any ventrolateral grooves.

Type material

Holotype GERMANY • Rhenish Mountains, Martenberg near Adorf ; middle Frasnian (Adorf Limestone); illustrated by Wedekind (1918: pl. 16 fig. 9, text-fig. 41) and Korn (2021a: text-fig. 2); SMF.Mbg.2328 .

Additional material

GERMANY • 1 spec.; Rhenish Mountains, Sessacker near Oberscheld ; middle Frasnian (Adorf Limestone); figured by Becker (1993, pl. 6 figs 4–5) and ( Korn 2021a, text-fig. 3c), re-illustrated here in Fig. 5 ; Beyrich Coll.; MB.C.834 • 1 spec.; Rhenish Mountains, Sessacker near Oberscheld ; middle Frasnian (Adorf Limestone); illustrated here in Fig. 5 ; Dannenberg Coll.; MB.C.30411 • 1 spec.; Rhenish Mountains, Sessacker near Oberscheld ; middle Frasnian (Adorf Limestone); illustrated here in Fig. 5 ; MB.C.4490 • 2 specs; Rhenish Mountains, near Oberscheld; middle Frasnian (Adorf Limestone); Lotz 1901–1902 Coll.; MB.C.30412.1–2 .

Description

Specimen MB.C.834 ( Fig. 5A )

Thinly discoidal specimen with 17 mm conch diameter; it has a compressed whorl profile (ww/dm = 0.38; ww/wh = 0.64). The flanks are convexly curved and converge to the rather narrow, evenly rounded venter. The specimen is fully chambered with few shell remains and shows the suture line characteristic of the genus Tornoceras with a broadly rounded, slightly asymmetrical adventive lobe and very small external lobe ( Fig. 5B ).

Specimens MB.C.30411 and MB.C.4490 ( Fig. 5C–D )

The other two specimens MB.C.30411 (13 mm dm; Fig. 5C ) and MB.C.4490 (8.5 mm dm; Fig. 5D ) confirm the conch morphology of the former specimen. In both, the shell is well preserved, bearing wide growth lines with high, narrow ventrolateral projection.

Remarks

Specimen MB.C.834 is the invalid neotype of the species. The existence of the actual original specimen in the collection of the University of Marburg, which is now preserved at the Senckenberg Museum (Frankfurt a. M.), made the determination of the neotype by Becker (1993) obsolete ( Korn 2021a). For a more detailed description of the species, see the latter paper.

Figures

Fig. 5. Tornoceras frechi Wedekind, 1918. A. Specimen MB.C.834 (Beyrich Coll.) from Sessacker near Oberscheld. B. Suture line of specimen MB.C.834 (Beyrich Coll.); at ww = 4.5 mm, wh = 5.5 mm. C. Specimen MB.C.30411 (Dannenberg Coll.) from Sessackernear Oberscheld.D. Specimen MB.C.4490 from Sessacker Oberscheld. Scale bar units = 1 mm.