Globimitoceras globiforme ( Vöhringer, 1960 )

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), European Journal of Taxonomy 882, pp. 1-230 : 29-31

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 .

Figures

Fig. 7. Early Tournaisian representative ammonoids of the family Prionoceratidae from the Hasselbachtal section, all Weyer 1993–1994 Coll. A. Mimimitoceras hoennense Korn, 1993, specimen MB.C.5241.2 from bed 59. B. Globimitoceras globiforme (Vöhringer, 1960), specimen MB.C.5240.7 from bed 57. C. Stockumites voehringeri sp. nov., paratype MB.C.5235.1 from bed 46. [Illustrated by Korn & Weyer (2003, pl. 1 figs 1–2) as Acutimitoceras cf. intermedium.] D. Stockumites intermedius (Schindewolf, 1923), specimen MB.C.5248.1 from bed 77. E. Stockumites convexus (Vöhringer, 1960), specimen MB.C.5241.1 from bed 59. F. Stockumites parallelus sp. nov., paratype MB.C.5247.2 from bed 57. (Illustrated by Korn & Weyer 2003: pl. 2 figs 6–7, as Acutimitoceras subbilobatum.) Scale bar units =1 mm.

Fig. 18. Globimitoceras globiforme (Vöhringer, 1960) from the Oberrödinghausen railway cutting. A. Paratype GPIT-PV-63921 (Vöhringer Coll.) from bed 3b. B. Specimen MB.C.31061 (Korn 1977 Coll.) from float material. C. Holotype GPIT-PV-63925 (Vöhringer Coll.) from bed 2. D. Specimen MB.C.31065 (Weyer 1993–1994 Coll.) from bed 3e. Scale bar units= 1 mm.

Fig. 19. Globimitoceras globiforme (Vöhringer, 1960) from the Oberrödinghausen railway cutting. A. Cross section of paratype GPIT-PV-63923 from bed 2. B. Cross section of paratype GPIT-PV-63934 from bed 3e. C. Suture line of holotype GPIT-PV-63925 from bed 2, at ww =20.5 mm, wh= 9.4 mm. D. Constriction course of specimen MB.C.31061, at dm =32.5 mm, ww =30.0 mm, wh =18.5 mm. E–G. Ontogenetic development of the conch width index (ww/dm), umbilical width index (uw/ dm), whorl width index (ww/wh) and whorl expansion rate (WER) of selected specimens. Scale bar units =1 mm.