Globimitoceras globiforme
Creators: name: Korn, Dieter
name: Weyer, Dieter
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Goniatitina
Prionoceratidae
Globimitoceras
Globimitoceras globiforme

description: Globimitoceras globiforme (Vöhringer, 1960)
Figs 7B, 18–19; Tables 8–9
Imitoceras globiforme Vöhringer, 1960: 145, pl. 1 fig. 2, text-fig. 22.
Globimitoceras globiforme – Korn 1993: 585; 1994: 36, text-figs 31a–b, 32a–c, 63b; 2006: text-fig. 3f. — Korn & Weyer 2003: 96, pl. 1 figs 11–12. — Sprey 2002, pl. 3 fig.5. — Becker & Weyer 2004: 18, text-fig. 3i–j. — Korn & Feist 2007: 103, text-fig. 4g –h.
non Imitoceras (Imitoceras) globiforme – Ruan 1981: 76, pl. 17 figs 1–16.
Diagnosis
Species of Globimitoceras with a conch reaching 60 mm diameter. Conch at 25 mm dm thinly globular (ww/dm ~0.95). Whorl profile at 25 mm dm moderately depressed (ww/wh ~1.80); coiling rate very low (WER ~1.45). Venter broadly rounded. Growth lines very fine with nearly linear course. Without constrictions on the shell surface; with internal shell thickenings. Suture line with very narrow, V-shaped external lobe and very narrow, V-shaped adventive lobe.
Material examined
Holotype
GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2; Vöhringer Coll.; illustrated by Vöhringer (1960: pl. 1 fig. 2a–b), Korn (1994: text-fig. 31b), Sprey (2002: pl. 3 fig. 5) and Korn (2006: text-fig. 3f); re-illustrated here in Fig. 18C; GPIT-PV- 63925.
Paratypes
GERMANY • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 2; Vöhringer Coll.; GPIT-PV- 63923 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3b; Vöhringer Coll.; GPIT-PV- 63921 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Vöhringer Coll.; GPIT-PV-63934, GPIT-PV-63998.
Additional material
GERMANY • 1specimen; RhenishMountains, Oberrödinghausen,railwaycutting; HangenbergLimestone, loose material; Korn 1977 Coll.; MB.C. 31061 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3b; Weyer 1993–1994 Coll.; MB.C. 31062 • 2 specimens; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d1b; Weyer 1993–1994 Coll.; MB.C. 31063.1–2 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d2; Weyer 1993–1994 Coll.; MB.C. 31064 • 1 specimen; Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Weyer 1993–1994 Coll.; MB.C. 31065 • 1 specimen; Rhenish Mountains, Hasselbachtal; Hangenberg Limestone, bed 57; Weyer 1993–1994 Coll.; MB.C.5240.7.
Description
Holotype GPIT-PV-63925 is a fairly well-preserved specimen (Fig. 18C). It has a spherical shape at 23 mm conch diameter (ww/dm ~0.95) and is almost completely involute with a very low coiling rate (WER ~1.50). Flanks and venter form an almost perfect semicircular arch. The suture line has a very narrow, lanceolate external lobe, separated from the very similar, weakly asymmetrical adventive lobe by a broadly rounded, inverted U-shaped ventrolateral saddle (Fig. 19C). Shell remains are not preserved.
Specimen MB.C.31061 is a well-preserved conch with a diameter of 36 mm (Fig. 18B). It is globular (ww/dm ~0.88) with a completely closed umbilicus and a very low coiling rate (WER ~1.42). The flanks and the venter form a semi-circular arch. The shell appears to be rather smooth, but it bears broad, weakly convex internal thickenings (Fig. 19D).
The two cross sections of the paratypes GPIT-PV-63923 (Fig. 19A) and GPIT-PV-63934 (Fig. 19B) allow the study of conch ontogeny from the initial stage to a diameter of 24 mm. The conch grows almost isometrically; all stages are very similar in their shape (Fig. 19 E-G). The whorl profile is C-shaped and narrows only slowly during ontogeny; the ww/wh ratio decreases from a value of ~2.15 at 1.5 mm diameter to ~1.75 at 24 mm diameter.
Remarks
Globimitoceras globiforme can be easily distinguished from all other globular ammonoids of the Hangenberg Limestone of Oberrödinghausen and other localities in the Rhenish Mountains by the conch with very low aperture throughout ontogeny. The species of Paragattendorfia show some similarities, but have a conch with a stepwise opening of the umbilicus and a suture line with a V-shaped external lobe and a V-shaped adventive lobe. Species of the genus Kornia are similar in the adult stage but produce a spindle-shaped juvenile conch. The growth lines, which are almost straight with shallow ventral sinus in G. globiforme, describe a very deep ventral sinus in the species of Kornia. Globimitoceras sphericum has a similar conch, but it is decorated with lamellar growth lines. In addition, G. sphericum has broader external and adventive lobes than G. globiforme.
description: Published as part of Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), pp. 1-230 in European Journal of Taxonomy 882 on pages 29-31, DOI: 10.5852/ejt.2023.882.2177, http://zenodo.org/record/8177581