Mimimitoceras hoennense Korn, 1993

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 : 25-27

Mimimitoceras hoennense Korn, 1993

Figs 7A , 16–17 ; Tables 4–5

Mimimitoceras hoennense Korn, 1993: 585 .

Imitoceras liratum – Vöhringer 1960: 125, pl. 2 fig. 2, text-fig. 5.

Mimimitoceras hoennense – Korn 1994: 18, text-figs 19b, d, 20e, 21e, 22d. — Korn & Weyer 2003: 100, pl. 2 figs 3–4.

“ Mimimitoceras ” hoennense – Becker & Weyer 2004: 22, text-figs 3a, 5c, 14–16.

non Mimimitoceras hoennense – Bockwinkel & Ebbighausen, 2006: 93, text-figs 6, 7c–d.

Diagnosis

Species of Mimimitoceras a conch reaching about 50 mm diameter. Conch thickly discoidal and involute (ww/dm ~0.55 at 30 mm dm); umbilicus closed at 8 mm dm. Whorl profile weakly depressed up to 30 mm dm and weakly compressed thereafter; coiling rate low (WER ~1.65). Ornament with fine and sharp, narrow-standing growth lines with convex course. Weak shell constrictions with convex course. Suture line with moderately wide, V-shaped external lobe and moderately wide, symmetric, V-shaped adventive lobe.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 2; Vöhringer Coll.; illustrated by Korn (1994, text-fig. 19b), re-illustrated in Fig. 16A ; GPIT-PV- 63884 .

Paratypes

GERMANY • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone , bed 3d; Vöhringer Coll.; GPIT-PV- 63867 • 1 specimen; Rhenish Mountains , Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 4; Vöhringer Coll.; GPIT-PV- 63866 .

Additional material

GERMANY • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 5; Vöhringer Coll.; MB.C. 31057 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 2b; Weyer 1993–1994 Coll.; MB.C. 31058 • 2 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3b; Weyer 1993– 1994 Coll.; MB.C. 31059.1–2 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3e; Weyer 1993–1994 Coll.; MB.C. 31060 • 1 specimen; Rhenish Mountains, Hasselbachtal ; Hangenberg Limestone , bed 59; Weyer 1993–1994 Coll.; MB.C. 5241.2 .

Description

Holotype GPIT-PV-63884 is a moderately preserved specimen with a diameter of 36.5 mm ( Fig. 16A ); it is strongly affected by preparation, but shows its ornamentation in addition to the conch form. The conch is thickly discoidal (ww/dm = 0.50) and completely involute (uw/dm = 0.01). On the shell surface very fine, wide growth lines with convex course are visible. In addition, fine shell constrictions occur at irregular intervals, which are accompanied by a barely discernible radial bulge on the apertural side.

The suture line of paratype GPIT-PV-63866 shows a narrow, V-shaped external lobe, which is accompanied by a symmetrical saddle that is rather narrowly rounded at the top. The V-shaped adventive lobe is also symmetrical ( Fig. 17B ).

The sectioned paratype GPIT-PV-63867 only allows a view into two whorls of maximum 15.5 mm conch diameter ( Fig. 17A ). These whorls are very similar in their horseshoe-shaped profile; only the ww/dm and ww/wh ratios decrease slightly ( Fig. 17 D-E).

Remarks

Mimimitoceras hoennense can be distinguished from M. perditum sp. nov. by the more slender conch (ww/dm at 20 mm dm ~0.60, but ~ 0.70 in M. perditum ). Mimimitoceras hoennense differs from the Late Devonian species of the genus with a slender conch, in the strongly convex course of the growth lines, which are slightly biconvex in M. geminum Korn, 1992 , nearly straight in M. lentum Korn, 1992 and weakly convex in M. alternum Korn, 1992 .

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. 16. Mimimitoceras hoennense Korn, 1993 from the Oberrödinghausen railway cutting, both Vöhringer Coll. A. Holotype GPIT-PV-63884 from bed 2. B. Paratype GPIT-PV-63866 from bed 2. Scale bar units= 1 mm.

Fig. 17. Mimimitoceras hoennense Korn, 1994 from the Oberrödinghausen railway cutting, all Vöhringer Coll. A. Cross section of paratype GPIT-PV-63867 from bed 3d. B. Suture line of paratype GPIT-PV-63866 from bed 4, at ww=13.5 mm, wh =12.0 mm. C. Growth line course of specimen GPIT- PV-63884 from bed 5, at dm =28.5 mm, ww ~ 15.0 mm, wh=14.6 mm. D–F. 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.