Costimitoceras ornatum 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 : 90-92

Costimitoceras ornatum Vöhringer, 1960

Figs 55–56 ; Tables 51–52

Costimitoceras ornatum Vöhringer, 1960: 148 , pl. 1 fig. 8, text-fig. 25.

Costimitoceras ornatum – Korn 1994: 53, text-figs 61a–b, 62a–b, 63d, 71a

Diagnosis

Species of Costimitoceras with a conch reaching 40 mm diameter. Conch thickly discoidal, subevolute at 5 mm dm (ww/dm ~0.55; uw/dm ~0.35); thickly discoidal, involute at 15 mm dm (ww/dm ~0.50; uw/dm ~0.05); thinly discoidal, involute at 25 mm dm (ww/dm ~0.40; uw/dm = 0.00). Whorl profile at 25 mm dm weakly compressed (ww/wh ~0.70); coiling rate high (WER ~2.10). Venter broadly rounded in the early and subadult stage, narrowly rounded in the adult stage. Growth lines coarse with biconvex course, coarse spiral lines. Without constrictions on the shell surface; without internal shell thickenings. Suture line with lanceolate external lobe and symmetric, V-shaped adventive lobe.

Material examined

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Vöhringer Coll.; illustrated by Vöhringer (1960: pl. 1 fig. 8) and Korn (1994: text-fig. 61a); re-illustrated here in Fig. 55A ; GPIT-PV-63918.

Paratype

GERMANY • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3d; Vöhringer Coll.; GPIT-PV-63920 • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Vöhringer Coll.; GPIT-PV-63922 .

Additional material

GERMANY • 1 specimen; Rhenish Mountains , Oberrödinghausen, railway cutting; Hangenberg Limestone, bed 3e; Weyer 1993–1994 Coll.; MB.C.31128 .

Description

Holotype GPIT-PV-63918 is a rather well-preserved specimen with 28 mm conch diameter ( Fig. 55A ). It has the shape of a thick lens (ww/dm ~0.40) with a closed umbilicus and a narrowly rounded venter. The coiling rate is high (WER ~2.10). The very conspicuous ornament consists of a combination of coarse, biconvex growth lines with a rather high dorsolateral projection ( Fig. 56D ) and a deep ventral sinus and almost equally coarse spiral lines, which are coarsest especially in the ventrolateral region. The suture line shows a lanceolate external lobe and a V-shaped adventive lobe with the same depth ( Fig. 56B ).

The smaller paratype GPIT-PV-63920 with 13 mm conch diameter is slightly stouter (ww/dm = 0.50) than the holotype and has a slightly open umbilicus ( Fig. 55B ). A distinct reticulate ornamentation is also developed in this specimen, but the spiral lines are restricted to the flank. The course of the sharp growth lines is concavo-convex, i.e. without a dorsolateral projection ( Fig. 56C ).

Remarks

Costimitoceras ornatum apparently does not differ from C. epichare in the shape of the conch as well as the ornamentation. Both species are only distinguished by the suture line, which has a lanceolate external lobe in C. ornatum , but which is V-shaped in C. epichare .

Figures

Fig. 55. Costimitoceras ornatum Vöhringer, 1960 from the Oberrödinghausen railway cutting, both Vöhringer Coll. A. Holotype GPIT-PV-63918 from bed 3e. B. Paratype GPIT-PV-63920 from bed 3d. Scale bar units= 1 mm.

Fig. 56. Costimitoceras ornatum Vöhringer, 1960 from the Oberrödinghausen railway cutting. A. Cross section of paratype GPIT-PV-63922 from bed 3e. B. Suture line of holotype GPIT-PV-63918 from bed 3e, at ww =7.7 mm, wh =8.5 mm. C. Growth line course of paratype GPIT-PV-63920 from bed 3d, at dm =10.5 mm, ww =5.5 mm, wh =5.5 mm. D. Growth line course of holotype GPIT-PV-63918 from bed 3e, at dm =28.0 mm, ww =11.5 mm, wh=15.5 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.