Stockumites kleinerae ( Korn, 1984 ) Korn & Weyer, 2023

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 : 47-51

Stockumites kleinerae ( Korn, 1984) comb. nov.

Figs 29–30 ; Tables 19–22

Acutimitoceras kleinerae Korn, 1984: 74 , pl. 1 figs 1–5, pl. 3 fig. 23, text-figs 4c–d, 5a.

Acutimitoceras kleinerae – Korn 1992b: 16, pl. 2 figs 4–5; 1994: 47, text-figs 36e, 38a–e, 40b, 44g –h, 45e, 48c–d, 56a–b, 57d–e. — Schönlaub et al. 1992: pl. 5 figs 4–5. — Kullmann 2000: text-fig. 4h. — Korn & Klug 2002: 197, text-fig. 173a.

Rectimitoceras substriatum – Sprey 2002: 52, text-fig. 17b.

Stockumites kleinerae – Korn & Weyer 2023 . — Korn & Weyer 2023: 16, figs 6–7.

Imitoceras Denckmanni – Schindewolf 1923: 336, pl. 15 figs 5–6, text-fig. 4h.

Imitoceras substriatum – Vöhringer 1960: 128, pl. 3 fig. 1, text-fig. 9.

non Acutimitoceras kleinerae – Sheng 1989: 110, pl. 33 figs 3–5.

Diagnosis

Species of Stockumites with a conch reaching 70 mm diameter. Conch at 5 mm dm pachyconic to globular, subinvolute to subevolute (ww/dm = 0.60–0.90; uw/dm = 0.20–0.40); at 15 mm dm pachyconic to globular, involute (ww/dm = 0.80–0.90; uw/dm = 0.05–0.15); at 30 mm dm thickly pachyconic, involute (ww/dm ~0.75; uw/dm = 0.00–0.05). Whorl profile at 30 mm dm weakly depressed (ww/wh ~1.35); coiling rate moderately high (WER ~1.80). Venter very broadly rounded, umbilical margin broadly rounded. Growth lines fine and rarely coarse, wide-standing, with convex course. Without constrictions on the shell surface; with weak internal shell thickenings. Suture line with narrow external lobe and narrowly V-shaped adventive lobe.

Material examined

Holotype

GERMANY • Rhenish Mountains , forestry road cutting 900 m east of Stockum ; Stockum Limestone ; Korn 1982 Coll.; illustrated by Korn (1984: pl. 1 fig. 3) and Korn (1994: text-fig. 38b); SMF 43001 .

Paratypes

GERMANY • 15 specimens; Rhenish Mountains , forestry road cutting, 900 m east of Stockum ; Stockum Limestone; Korn 1982 Coll.; SMF 43002 – SMF 43016 • 13 specimens; Rhenish Mountains , trench II , 950 m east of Stockum ; Stockum Limestone; Korn 1982 Coll.; SMF 43017 – SMF 43029 • 10 specimens; Rhenish Mountains , Müssenberg ; Hangenberg Limestone, bed 3c; Korn 1980 Coll.; SMF 43030 – SMF 43039.

Additional material

GERMANY • 4 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 5; Vöhringer Coll.;GPIT-PV-63879, GPIT-PV-63880, GPIT-PV-64014, GPIT-PV-64016 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 6; Vöhringer Coll.; GPIT-PV-64004 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 4; Vöhringer Coll.; MB.C.31074 • 2 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 5; Vöhringer Coll.; MB.C.31075.1– 2 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 6; Vöhringer Coll.; MB.C.31076 • 1 specimen; Rhenish Mountains, Oberrödinghausen , road cutting; Hangenberg Limestone , bed 6; Korn 1977 Coll.; MB.C.31077 • 1 specimen; Rhenish Mountains, Hasselbachtal ; Hangenberg Limestone , bed 83; Weyer 1993–1994 Coll.; MB.C.5251.4 • 1 specimen; Rhenish Mountains, Oese , old quarry ; bed interval III ; Paproth Coll.; MB.C.5272.

Description

GPIT-PV-63880 is the largest available specimen with a conch diameter of 55 mm ( Fig. 29A ). Even at this diameter, the conch is still thinly pachyconic (ww/dm = 0.64). The umbilicus is completely closed, the umbilical margin is rounded and the convex flanks merge continuously into the broadly rounded venter. The coiling rate is moderate (WER = 1.91).

The smaller specimen GPIT-PV-64004 ( Fig. 29B ) with 24 mm conch diameter is thickly pachyconic (ww/dm = 0.78) and shows a low coiling rate (WER = 1.67). It bears a delicate ornament with fine growth lines that are directed slightly backwardly on the flank. They have a weakly biconvex course with a shallow ventral sinus ( Fig. 30D ). Shell constrictions are not visible.

The suture line of specimen GPIT-PV-64016 shows a very narrow, lanceolate external lobe separated from the adventive lobe by a three times wider, broadly rounded ventrolateral saddle. The symmetric adventive lobe is V-shaped and wider than the external lobe ( Fig. 30C ).

Remarks

Stockumites kleinerae belongs to the species of the genus with the stoutest conch. The ww/dm ratio, even in the adult stage of 55 mm conch diameter, is greater than 0.60, surpassing almost all other species. The whorl profile is always depressed in S. kleinerae (ww/wh larger than 1.00)

The material of S. kleinerae shows some variation of the umbilical width of the inner whorls. Even the type material from Stockum shows this variation; specimen SMF 43002 ( Korn 1984: text-fig. 5a) is evolute (uw/dm = 0.45 at 2 mm dm), while the other specimens from Stockum only reach a uw/dm ratio of about 0.30. The inner whorls of the sectioned specimens from Oberrödinghausen are even less widely umbilicate; they reach a uw/dm ratio of only 0.30 ( Fig. 30E ).

Stockumites kleinerae differs from the stratigraphically younger species S. depressus in the lack of the internal shell thickenings, which cause conspicuous constrictions of the internal mould in the latter species.

Figures

Fig. 29. Stockumites kleinerae (Korn, 1984) from the Oberrödinghausen railway cutting, both Vöhringer Coll. A. Specimen GPIT-PV-63880 from bed 5. B. Specimen GPIT-PV-64004 from bed 6. Scale bar units =1 mm.

Fig. 30. Stockumites kleinerae (Korn, 1984) from the Oberrödinghausen railway cutting.A. Cross section of specimen GPIT-PV-63879 from bed 5. B. Cross section of specimen MB.C.31075.1 from bed 5. C. Suture line of specimen GPIT-PV-64016 from bed 5, at ww =10.5 mm. D. Growth line course of specimen GPIT-PV-64004 from bed 6, at dm = 23.0 mm, ww =19.4 mm, wh =12.8 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.