Pharciceras oberscheldense Bockwinkel & Korn, 2013

Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 771, pp. 1-79 : 15-19

Pharciceras oberscheldense Bockwinkel & Korn in Bockwinkel et al., 2013

Figs 10–13 ; Tables 4–5

Pharciceras oberscheldense Bockwinkel & Korn in Bockwinkel et al., 2013b: 262, text-figs 5–8.

Prolecanites tridens – Frech 1888: 29, pl. 2 fig. 5. — Wedekind 1918: 128, text-fig. 37a.

Pharciceras oberscheldense – Bockwinkel & Korn 2017: 201, text-figs 13–14.

Diagnosis

Species of Pharciceras with thickly discoidal, subevolute conch at 25 mm dm (ww /dm ~ 0.50; uw/ dm ~ 0.32) and thinly discoidal, subevolute conch at 60 mm dm (ww/ dm ~ 0.35; uw / dm ~ 0.30). Whorl profile weakly depressed at 25 mm dm (ww/ wh ~ 1.35) and weakly compressed at 60 mm dm (ww / wh ~ 0.90); whorl expansion rate low to moderate. Venter continuously rounded throughout ontogeny. Adult stage with slightly flattened, converging flanks bordered by a subangular ventrolateral shoulder from the slightly flattened venter. Growth lines coarse, strongly biconvex; ventrolateral shoulder with two spiral grooves. Outer suture line with asymmetric, rounded prongs of the external lobe, a tongue-shaped lateral lobe, a small V-shaped U 2 lobe, and a shallow and wide U 4 lobe.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld (Grube Sahlgrund); late Givetian (Red Ironstone); Kegel 1929 Coll.; illustrated by Bockwinkel et al. (2013b: text-fig. 5), re-illustrated here in Fig. 10A ; MB.C.3620 .

Paratypes GERMANY • 1 specimen; Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); Dannenberg Coll.; MB.C.3655 • 1 specimen; Rhenish Mountains , Oberscheld (Westfeld der Grube Königszug, Firste der 120–150 m Sohle); late Givetian (Red Ironstone); Ahlburg Coll.; MB.C.3662 • 1 specimen; Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); Krüger 1873 Coll.; MB.C.22161 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Prinzkessel); late Givetian (Red Ironstone); Becker 1902 Coll.; MB.C.22168 .

Additional material

GERMANY • 3 specimens; Rhenish Mountains , Oberscheld (Grube Prinzkessel); late Givetian (Red Ironstone); Welsch 1905 Coll.; SMF.Mbg.6362–6364 • 2 specimens; Rhenish Mountains , Oberscheld (Westfeld der Grube Königszug, Firste der 120–150 m Sohle); late Givetian (Red Ironstone); Ahlburg Coll.; MB.C.3614 , MB.C.3622 • 3 specimens; Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); Lotz 1901–1902 Coll.; MB.C.22156 , MB.C.22167 , MB.C.30232 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Volpertseiche); late Givetian (Red Ironstone); Bender 1901 Coll.; MB.C.30233 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Königszug, 60 m Sohle); late Givetian (Red Ironstone); Lotz 1902 Coll.; MB.C.30234 .

Description

Eight specimens are selected for description and illustration: Holotype MB.C.3620: incomplete specimen with 76 mm conch diameter in iron-rich sparitic limestone. A segment of the last volution is missing, allowing the study of the penultimate whorl ( Fig. 10A ).

Paratype MB.C.3655: incomplete specimen with 48 mm conch diameter in iron-rich limestone; probably the last volution belongs to the body chamber ( Fig. 10D ).

Paratype MB.C.3662: incomplete specimen with 33 mm conch diameter in iron-rich micritic limestone; the specimen is filled with sparry calcite. The specimen is fully chambered, body chamber missing.

Paratype MB.C.22161: fairly well-preserved specimen with 65 mm conch diameter in haematitic limestone. The specimen is broken apart and allows the study of an inner whorl and its suture line ( Figs 10B , 11A ).

Paratype MB.C.22168: incomplete steinkern specimen with 47 mm conch diameter in iron-rich limestone; the complete last volution belongs to the body chamber ( Fig. 10C ).

Specimens SMF.Mbg.6362–6364: three specimens between 32 and 43 mm conch diameter in iron-rich limestone ( Fig. 10E–G ).

Hototype MB.C.3620 has in the last volution at 76 mm diameter a discoidal and subevolute conch (ww / dm =0.32; uw/ dm =0.31) with moderately high coiling rate (WER ~1.87); the whorl profile is compressed (ww / wh=0.77) with narrow umbilical wall and slightly flattened flanks which converge towards the subangular ventrolateral shoulder. In the penultimate whorl, the venter is broadly rounded. Here, two shallow ventrolateral spiral grooves are accompanied by low ridges on each side. Lamellose growth lines are well-preserved here and extend with a wide dorsolateral projection, a broad lateral sinus, and a very pronounced, narrow ventrolateral projection across the flanks. The suture line has, at approximately 34 mm conch diameter, a very wide external lobe, in which the prongs are slightly pouched. Two V-shaped lobes are located on the flank ( Fig. 11A ), a narrowly rounded U 2 and a shallow and wide A

4

lobe.

The smaller paratypes confirm the morphology visible in the penultimate whorl of the holotype. They show that, between 28 and 60 mm conch diameter, the conch shape becomes slenderer (ww/ dm reduced from ~ 0.45 to ~0.30), while the umbilical width ratio is rather stable (uw / dm =0.30–0.35).

Remarks

Pharciceras oberscheldense is a common species in the Red Ironstone from Dillenburg and specimens of this species were obviously often referred to as P. tridens . This includes the specimen figured by Frech (1888), which cannot be assigned to P. tridens because of its rather narrow umbilicus, which has only one third of the conch diameter ( Fig. 12 ) and probably also the specimen figured by Wedekind (1918: pl. 20 fig. 7) ( Fig. 13 ).

Pharciceras oberscheldense belongs to the more narrowly umbilicate species of the genus (uw / dm ~ 0.30 at 30–40 mm dm) and differs in this respect from P. tridens and P. kochi sp. nov. (uw / dm ~ 0.40). Among the narrowly umbilicate species of Pharciceras , P. oberscheldense differs from P. ferrum sp. nov. in the shape of the lateral lobe (rounded in P. oberscheldense but V-shaped in P. ferrum sp. nov.) and in the wider whorl profile (ww/ wh ~ 1.05 at 50 mm dm in P. oberscheldense but only ~ 0.80 in P. ferrum sp. nov.).

Figures

Fig. 10. Pharciceras oberscheldense Bockwinkel & Korn in Bockwinkel et al., 2013. A. Holotype MB.C.3620 (Kegel 1927 Coll.) from Oberscheld (Sahlgrund Mine). B. Paratype MB.C.22161 (Krüger 1873 Coll.) from Oberscheld. C. Paratype MB.C.22168 (Becker 1902 Coll.) from Oberscheld (Prinzkessel Mine). D. Paratype MB.C.3655 (Dannenberg Coll.) from Oberscheld. E. Specimen SMF.Mbg.6363 (Welsch 1905 Coll.) from Oberscheld (Prinzkessel Mine). F. Specimen SMF.Mbg.6362 from Oberscheld. G. Specimen SMF.Mbg.6364 (Welsch 1905 Coll.) from Oberscheld (Prinzkessel Mine). Scale bar units = 1 mm.

Fig. 11. Pharciceras oberscheldense Bockwinkel & Korn in Bockwinkel et al., 2013. A. Suture line of paratype MB.C.22161 (Krüger 1873 Coll.), at wh =12.9 mm. B–E. Ontogeneric trajectories of the cardinal conch parameters. Abbreviation: see Material and methods. Scale bar units = 1 mm.

Fig. 12. Pharciceras oberscheldense Bockwinkel & Korn in Bockwinkel et al., 2013, reproduction of the specimen illustrated in Frech (1888: pl. 2 fig. 5). Scale bar units = 1 mm.

Fig. 13. Pharciceras oberscheldense Bockwinkel & Korn in Bockwinkel et al., 2013, the probably lost specimen figured by Wedekind (1918: pl. 20 fig. 7) as Pharciceras tridens(Sandberger & Sandberger, 1850) from Langenaubach (Constanze Mine). Scale bar units = 1 mm.