Stockumites intermedius ( Schindewolf, 1923 )

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 : 51-57

Stockumites intermedius ( Schindewolf, 1923)

Figs 7D , 31–34 ; Tables 23–26

Imitoceras intermedium Schindewolf, 1923: 333 , pl. 16 fig. 2, text-fig. 4f.

Imitoceras intermedium – Librovitch 1940: pl. 2 fig. 5a–b. — Vöhringer 1960: 131, pl. 3 figs 2, 7–8, text-fig. 11. — Furnish & Manger 1973: 20, text-fig. 2b, d. — Weyer 1977: 177, text-fig. 2.1. — House 1985: pl. 6.7.29, text-fig. 6.7.14b.

Acutimitoceras intermedium – Korn 1984: 75, pl. 3 figs 20–23, text-figs 4e, 5h–I; 1992b: 15, pl. 1 figs 22–27, 30, pl. 2 figs 2–3, 7–9, 15–16, 21–22, 26–27; 1992c: 178, pl. 1 figs 7–11; 1994: 47, text-figs 37a–c, 40c, 41a–e, 44a–c, 45a–c, 47b, 48a–b, 56d–f, 57b–c. — Schönlaub et al. 1992: pl. 4 figs 22–27, 30, pl. 5 figs 2–3, 7–9, 15–16, 21–22, 26–27. — Korn et al. 1994: text-fig. 20b. — Kullmann,2000: text-fig. 4g. — Korn & Klug 2002: 197, text-fig. 173b. — Korn & Weyer 2003: pl. 2 figs 12–13.

Acutimitoceras (Stockumites) intermedium – Sprey 2002: 52, text-fig. 17e.

Stockumites intermedius – Korn & Weyer 2023: 20 , figs 8–9.

Aganides infracarbonicus – Schmidt 1924: 149, pl. 8 figs 1–2; 1929: 61, pl. 15 fig. 8.

non Imitoceras intermedium – Librovitch 1940: 138, pl. 35 figs 2–3. — Schindewolf 1952: 291, textfigs 4–6. — Balashova 1953: 198, pl. 12 figs 11–20. — Furnish & Manger 1973: 20, pl. 1 figs 11–15.

non Imitoceras (Imitoceras) intermedium – Ruan 1981: 64, pl. 12 figs 1–6, 9–13, 17–28.

non Acutimitoceras intermedium – Belka et al. 1999: pl. 5 figs 7–8. — Korn 1999: 166, pl. 2 fig. 8. — Bockwinkel & Ebbighausen 2006: 97, text-figs 13–14. — Ebbighausen & Bockwinkel 2007: 131, text-figs 8f–g, 10, 12a–b. — Korn & Feist 2007: 106, text-fig. 6b–c, h.

non Stockumites intermedius – Becker et al. 2002: pl. 2 figs 13–14.

Diagnosis

Species of Stockumites with a conch reaching 120 mm diameter. Conch at 5 mm dm thinly pachyconic, subinvolute to subevolute (ww/dm ~0.70; uw/dm = 0.20–0.40); at 15 mm dm thinly pachyconic, involute (ww/dm ~0.65; uw/dm ~0.00); at 30 mm dm thinly pachyconic, involute (ww/dm ~0.65; uw/ dm ~0.00). Whorl profile at 30 mm dm weakly depressed (ww/wh = 1.10–1.20); coiling rate moderately high (WER = 1.85–1.95). Venter broadly rounded, umbilical margin very broadly rounded. Growth lines lamellar, wide-standing, with convex or weakly biconvex course. Without constrictions on the shell surface; without internal shell thickenings. Suture line with narrowly lanceolate external lobe and narrowly V-shaped adventive lobe.

Material examined

Lectotype

GERMANY • Upper Franconia, 400 m north-west of Kirchgattendorf ; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1916 Coll.; illustrated by Schindewolf (1923: pl. 16 fig. 2), ( Librovitch 1940: pl. 2 fig. 5), Korn (1994: text-fig. 56f) and ( Korn & Weyer 2023: fig. 8a); SMF Mbg.3111.

Paralectotypes

GERMANY • 9specimens; Upper Franconia , 400 m north-west of Kirchgattendorf; bed 21 (“ Gattendorfia Limestone ”); Schindewolf 1916 Coll.; SMF Mbg.7563– SMF Mbg.7571.

Additional material

GERMANY • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 3e; Vöhringer Coll.; GPIT-PV-64002 • 5 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 5; Vöhringer Coll.; GPIT-PV-63860, GPIT-PV-63892, GPIT-PV-63993, GPIT-PV-64000, GPIT-PV-64015 • 2 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 6; Vöhringer Coll.; GPIT- PV-63875, GPIT-PV-63891 • 9 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 5; Vöhringer Coll.; MB.C.31078.1–9 • 3 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 6; Vöhringer Coll.; MB.C.31079.1– 3 • 9 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 5a2; Weyer 1993–1994 Coll.; MB.C.31080.1–9 • 3 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting; Hangenberg Limestone , bed 5b; Weyer 1993–1994 Coll.; MB.C.31081.1–3 • 1 specimen; Rhenish Mountains, Oberrödinghausen , road cutting; Hangenberg Limestone , bed 5; Korn 1977 Coll.; MB.C.31082 • 1 specimen; Rhenish Mountains, Oberrödinghausen , road cutting; Hangenberg Limestone , bed 6; Korn 1977 Coll.; MB.C.31083 • 1 specimen; Rhenish Mountains, Hasselbachtal ; Hangenberg Limestone , bed 77; Weyer 1993–1994 Coll.; MB.C.5248.1 • 1specimen; Rhenish Mountains, Hasselbachtal ; Hangenberg Limestone , bed 80; Weyer 1993–1994 Coll.; MB.C.5249.3 • 1 specimen; Rhenish Mountains, Oese , old quarry; Hangenberg Limestone ; Korn 1977 Coll.; MB.C.31084.

Description

The two specimens GPIT-PV-63993 (52 mm dm; Fig. 31A ) and GPIT-PV-64015 (34 mm dm; Fig. 31B ) represent the adult and preadult stages of the species. The former has a thickly discoidal shape (ww/dm = 0.53) with a completely closed umbilicus, strongly convex flanks and a continuously rounded venter. The coiling rate is moderately high (WER = 1.92). The shell surface bears an ornament of weakly biconvex growth lines running backwardly across the flank and form a broad ventral sinus ( Fig. 33D ; the growth lines appear to be widely lamellar especially on the outer flank.

The smaller specimen GPIT-PV-64015 ( Fig. 31B ) has similar conch proportions to the previously described specimen, but with a lower coiling rate (WER = 1.82). It shows the suture line, which has a lanceolate external lobe with weakly divergent flanks. The ventrolateral saddle is about twice as wide as the external lobe and broadly rounded. The almost symmetrical, V-shaped adventive lobe has weakly convexly curved flanks ( Fig. 33C ).

Ten cross sections are available for examination, of which seven show the ontogeny beginning with the initial stage. They all show the characteristic, very broadly rounded umbilical margin and the continuously rounded venter. The main differences between the specimens are in the shape of the inner whorls. These are always subevolute or evolute with a crescent-shaped profile, but this evolute stage varies in length: In the two cross sections of specimens from bed 6 ( Fig. 32A–C ), only two whorls are widely umbilicate, while in the five specimens from bed 5 ( Figs 33–34 ), three or even four whorls are evolute. This means that the maximum uw/dm value reaches ~ 0.40 in the specimens from bed 6, but ~ 0.50 in the specimens from bed 5 ( Figs 32E , 33E ). The early ontogenetic, subevolute to evolute stage is followed by a middle stage in which the whorl profile is C-shaped. At about 8 mm conch diameter, the umbilicus begins to close. This process is already completed at a conch diameter of 15–20 mm. At this stage, the whorl profile is already horseshoe-shaped with increasing whorl height.

Remarks

In his monograph on the ammonoids from the Hangenberg Limestone, Vöhringer (1960) grouped specimens of two species under the name “ Imitoceras intermedium ”: (1) specimens from beds 6 and 5, which actually correspond in morphology to the type material of this species from Gattendorf and (2) non-illustrated specimens from beds 3 and 2, which belong to the here newly described species Stockumites voehringeri sp. nov. The latter differs from S. intermedius by the slightly more slender conch and particularly by the presence of internal shell thickenings in the area of the outer flank and venter.

Stockumites intermedius differs from the co-occurring species S. kleinerae by the more slender conch (ww/dm = 0.60–0.65 in S. intermedius , but 0.75–0.80 in S. kleinerae at 30 mm dm). In addition, S. intermedius has lamellar growth lines, which are finer in S. kleinerae and are there also visible because of rhythmic strengthening on the inner surface of the shell, causing fine undulation of the internal mould.

Other species of Stockumites with comparable pachyconic conch are distinguished from S. intermedius by the shell constrictions or internal shell thickenings. A morphologically similar species is S. depressus , but this has more strongly biconvex, fine and narrow-standing growth lines.

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. 31. Stockumites intermedius (Schindewolf, 1923) from the Oberrödinghausen railway cutting, bed 5. A. Specimen GPIT-PV-63993 (Vöhringer Coll.). B. Specimen GPIT-PV-64015 (Vöhringer Coll.). Scale bar units = 1 mm.

Fig. 32. Stockumites intermedius (Schindewolf, 1923) from bed 6 of the Oberrödinghausen railway cutting; all Vöhringer Coll. A. Cross section of specimen GPIT-PV-63875. B. Cross section of specimen MB.C.31079.1. C. Cross section of specimen MB.C.31079.2. D. Growth line course of specimen GPIT- PV-63875, at dm =22.5 mm, ww =16.6 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. Grey dots =representatives from bed 5. Scale bar units= 1 mm.

Fig. 33. Stockumites intermedius (Schindewolf, 1923) from bed 5 of the Oberrödinghausen railway cutting; all Vöhringer Coll. A. Cross section of specimen MB.C.31078.1. B. Cross section of specimen MB.C.31078.2. C. Suture line of specimen GPIT-PV-64015, at dm =28.2 mm, ww =21.0 mm, wh= 14.8 mm. D. Growth line course of specimen GPIT-PV-63993, at ww =22.0 mm, wh =20.0 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. Grey dots =representatives from bed 6. Scale bar units =1 mm.

Fig. 34. Stockumites intermedius (Schindewolf, 1923) from bed 5 of the Oberrödinghausen railway cutting. A. Cross section of specimen MB.C.31078.3 (Vöhringer Coll.). B. Cross section of specimen MB.C.31080.1 (Weyer 1993–1994 Coll.) from bed 5a2. C. Cross section of specimen GPIT-PV-64000 (Vöhringer Coll.). D. Cross section of specimen MB.C.31078.4 (Vöhringer Coll.) from bed 5. E. Cross section of specimen GPIT-PV-63860 (Vöhringer Coll.). Scale bar units =1 mm.