Pseudarietites westfalicus Schmidt, 1924

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 : 180-183

Pseudarietites westfalicus Schmidt, 1924

Figs 8E , 110–112 ; Tables 106–107

Pseudarietites westfalicus Schmidt, 1924: 152 , pl. 8 fig. 12.

Pseudarietites westfalicus – Schmidt 1925: 536, pl. 19 fig. 7. — Korn 1994: 78, text-figs 70d–e, 71d, 72b; 2006: text-fig. 4d. — Kullmann 2009: text-fig. 5.2b–c.

Pseudarietites westfalicus westfalicus – Vöhringer 1960: 163, pl. 6 fig. 11, text-fig. 40. — Weyer 1965: 448.

Diagnosis

Species of Pseudarietites with a conch reaching 40 mm diameter. Conch at 15 mm dm thinly discoidal, subevolute (ww/dm ~0.40; uw/dm ~0.42). Whorl profile at 15 mm dm weakly depressed (ww/wh ~1.25); coiling rate low (WER ~1.70). Venter broadly rounded with distinct keel between two distinct grooves, umbilical margin rounded. On the flank 25 sharp ribs with concave course.

Holotype

GERMANY • Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone ; Schmidt Coll.; illustrated by Schmidt (1924: pl. 8, fig. 12) and Korn (2006: text-fig. 4d); re-illustrated here in Fig. 110 ; BGRB X5716.

Additional material

GERMANY • 3 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone ; Schindewolf 1925 Coll.; MB.C.31212.1–3 • 2 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3b ; Vöhringer Coll.; GPIT- PV-63978, GPIT-PV-63980 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3c; Vöhringer Coll.; GPIT-PV-63982 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3 a; Korn 1991 Coll.; MB.C.31213 • 22 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3 a; Weyer 1993–1994 Coll.; MB.C.31214.1–22 • 8 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3b ; Weyer 1993–1994 Coll.; MB.C.31215.1–8 • 7 specimens; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3c1 ; Weyer 1993–1994 Coll.; MB.C.31216.1–7 • 1 specimen; Rhenish Mountains, Oberrödinghausen , railway cutting ; Hangenberg Limestone , bed 3c2 ; Weyer 1993–1994 Coll.; MB.C.31217 • 1 specimen; Rhenish Mountains, Oberrödinghausen , road cutting ; Hangenberg Limestone , bed 3b ; Korn & Weyer 2000 Coll.; MB.C.31218 • 1 specimen; Rhenish Mountains, Hasselbachtal ; Hangenberg Limestone , bed 49 ; Weyer 1993–1994 Coll.; MB.C.5236.1 • 1 specimen; Rhenish Mountains, Oese , old quarry ; Hangenberg Limestone , bed 30 ; Weyer & Korn 2000 Coll.; MB.C.5258.2 • 1 specimen; Rhenish Mountains, Oese , old quarry ; Hangenberg Limestone , bed 28 ; Weyer & Korn 2000 Coll.; MB.C.5260.4 • 1 specimen; Rhenish Mountains, Oese , old quarry ; bed interval VI ; Paproth Coll.; MB.C.5282.

Description

Holotype BGRB X5716 is a specimen with nearly 15 mm conch diameter and allows the examination of two whorls ( Fig. 110 ). It is thinly discoidal and subevolute (ww/dm = 0.42; uw/dm = 0.45) with a weakly depressed whorl profile (ww/wh = 1.28). The venter possesses two shallow longitudinal grooves with a rounded keel rising between them. On the last volution there are about 24 sharp ribs; these ribs form sharp nodes around the umbilicus and become weaker towards the flank. In the area of the outer flank they bend slightly forward and form a low projection before they diminish. Faint growth lines follow the course of the ribs; they form a low ventrolateral projection and a deep, broadly rounded ventral sinus. The penultimate whorl possesses 24 ribs.

The smaller, well-preserved specimen MB.C.31214.1 has a conch diameter of 14.5 mm and is also thinly discoidal and subevolute (ww/dm = 0.39; uw/dm = 0.43). In the sculpture it closely resembles the holotype; it has 26 ribs on the last and 24 ribs on the penultimate whorl ( Fig. 112A ). The ventral grooves are slightly deeper than in the holotype.

The incomplete ontogeny preserved in the sectioned specimen GPIT-PV-63982 shows a whorl profile that is, between 4 and 7.5 mm conch diameter, depressed crescent-shaped with a ww/wh ratio being reduced from 1.70 to 1.50. A raised ventral keel is present at 9.8 mm dm.

Larger specimens (e.g., specimens GPIT-PV-63978 and GPIT-PV-63980) show that the whorl profile becomes circular at 27 mm dm ( Fig. 111A–B ).

The growth trajectories are essentially consistent with those from the other representatives of the subfamily. Almost all trajectories are close to monophasic in the interval between 4 and 27 mm conch diameter with only minor changes of the conch ratios ( Fig. 112C–E ).

Remarks

Pseudarietites westfalicus differs from the very similar P. silesiacus in the lower number of ribs (25 in P. westfalicus but 30 in P. silesiacus ). Pseudarietites westfalicus can be separated from P. subtilis by the much wider umbilicus (uw/dm = 0.45 in P. westfalicus at 20 mm dm but about 0.35 in P. subtilis ).

Figures

Fig. 8. Early Tournaisian representative ammonoids of the family Gattendorfiidae from the Hasselbachtal section, all Weyer 1993–1994 Coll. A. Gattendorfia rhenana sp. nov., paratype MB.C.5244.1 from bed 71. (Illustrated by Korn & Weyer 2003: pl. 2 figs 10–11, as Gattendorfia subinvoluta.) B. Weyerella molaris (Vöhringer, 1960), specimen MB.C.5240.8 from bed 57. C. Weyerella reticulum (Vöhringer, 1960), specimen MB.C.5242.1 from bed 62. D. Hasselbachia multisulcata (Vöhringer, 1960), specimen MB.C.5240.1 from bed 57. E. Hasselbachia gracilis (Vöhringer, 1960), specimen MB.C.5240.5 from bed 57. F. Pseudarietites westfalicus Schmidt, 1924, specimen MB.C.5236.1 from bed 49. Scale bar units =1 mm.

Fig. 110. Pseudarietites westfalicus Schmidt, 1924 from the Oberrödinghausen railway cutting, holotype BGRB X5716 (Schmidt Coll.), bed unknown. Reproduction of the figure by Schmidt (1924: pl. 8 fig. 12) and photographs. Scale bar units =1 mm.

Fig. 111. Pseudarietites westfalicus Schmidt, 1924 from the Oberrödinghausen railway cutting, both Vöhringer Coll. A. Specimen GPIT-PV-63978 from bed 3b. B. Specimen GPIT-PV-63980 from bed 3b. Scale bar units = 1 mm.

Fig. 112. Pseudarietites westfalicus Schmidt, 1924 from the Oberrödinghausen railway cutting. A. Specimen MB.C.31214.1 (Weyer 1993–1994 Coll.) from bed 3a. B. Cross section of specimen GPIT- PV-63982 (Vöhringer Coll.) from bed 3c.C. Growth line course of specimen GPIT-PV-63980 (Vöhringer Coll.) from bed 3b, at dm = 24.5 mm, ww =8.2 mm, wh= 8.2 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.