Synpharciceras clavilobum ( Sandberger & Sandberger, 1850 )

Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 771, pp. 1-79 : 59-61

Synpharciceras clavilobum ( Sandberger & Sandberger, 1850)

Figs 43–45 ; Table 27

Goniatites clavilobus Sandberger & Sandberger, 1850: 67 , pl. 8 fig. 3.

Prolecanites clavilobus – Frech 1902: 63, pl. 2 fig. 10.

Synpharciceras clavilobum – Kullmann & Ziegler 1970: 79, pl. 1 figs 6–7, text-figs 2d, 3d. — House in House & Ziegler 1977: 80, pl. 5 figs 18–19. — Korn & Klug 2002: 145, text-figs 134j (only).

non Pharciceras clavilobum – Wedekind 1918: 127, pl. 20 figs 4–5, text-fig. 37d.

non Sympharciceras clavilobum – Petter 1959: 147, pl. 7 fig. 15, pl. 8 figs 2–3, 6–8, text-figs 33c, 38. — Bogoslovsky 1969, pl. 26 fig. 3. — Bensaïd 1974: 115, pl. 5 figs 2, 5, text-fig. 19d. — Korn 1999: text-fig. 2b. — Klug & Korn 2002: 922, text-fig. 4b. — Korn & Klug, 2002: 145, text-figs 134c, f, i, 135c. — Bockwinkel et al. 2009: 114, text-figs 26–27, 28d–e; 2013a: 50, text-figs 51–52; 2015: 146, text-figs 27a–c, 28a, c–d; 2017: 343, text-figs 32–33.

Diagnosis

Synpharciceras with thinly discoidal conch at 30 mm dm (ww/ dm ~ 0.45) with closed umbilicus. Whorl profile slightly compressed (ww/ wh ~0.95); conch widest near the umbilicus. Flanks and venter continuously rounded; venter bordered by faint ventrolateral spiral grooves. Outer suture line with weakly pouched, blunt, E 2, L and U 2 lobes meandering with separating rounded saddles. Inner flank and umbilical wall with blunt U 4, U 6, U 8 and U 10 lobes.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld ( Grube Königszug ); late Givetian (Red Ironstone); 42 (Wiesbaden Museum); illustrated by Sandberger & Sandberger (1850 –1856: pl. 8 fig. 3), House & Ziegler (1977: pl. 5 figs 18–19) and Bockwinkel et al. (2013a: text-fig. 52e); Wiesbaden Museum nr. 42. ( Fig. 43 )

Additional material

GERMANY • 3 specimens; Rhenish Mountains , Oberscheld ( Grube Gründchesseite ); late Givetian (Red Ironstone); Lotz 1901 Coll.; MB.C.3653 , MB.C.30260 , MB.C.30261 • 2 specimens; Rhenish Mountains , Oberscheld ( Grube Anna ); late Givetian (Red Ironstone); Koch Coll.; MB.C.22190 , MB.C.22191 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Königszug, 60 m Lager); late Givetian (Red Ironstone); Lotz 1902 Coll.; MB.C.30259 .

Description

Holotype 42 in the Wiesbaden Museum is a rather well-preserved, partly exfoliated specimen with 32 mm diameter, at which the conch dimensions can be obtained at 29 mm diameter ( Fig. 43 ). It is thinly discoidal (ww/ dm = 0.48) with an almost closed umbilicus, but this area is obscured by matrix. The whorl profile is weakly compressed (ww/ wh =0.93); it is widest near the umbilicus, from where the convex flanks converge towards the continuously rounded venter. On the venter, there are two weak spiral grooves standing 4 mm apart. The suture line of the specimen shows a meandering outline with weakly pouched E 2, L and U 2 lobes similar in outline; they are rounded at the base ( Fig. 45A ). They are separated by rather narrow, rounded saddles.

MB.C.3653: fully septate specimen with 34 mm conch diameter in iron-rich micritic limestone, partly filled with sparry calcite ( Fig. 44A ). It is discoidal (ww / dm =0.47) with closed umbilicus; the whorl profile is slightly compressed (ww / wh= 0.86) and the coiling rate is low (WER= 1.72). Shell ornament is not preserved. The specimen is covered by a delicate Runzelschicht, which lines extend with a low ventrolateral projection and a shallow ventral sinus. The outer suture line is rather regularly meandering with elements becoming smaller towards the umbilicus ( Fig. 45B ). The E 1 lobe is funnel-shaped, the lateral prong and the L and U 2 lobes are weakly pouched and blunt, while the U 4 and U 6 lobes are linguiform.

MB.C.22191 is a moderately preserved specimen with 25 mm conch diameter in haematitic limestone ( Fig. 44B ).

Remarks

Synpharciceras clavilobum is a rare species; only a few characteristic specimens are known from the type region. It differs from the more common species Pluripharciceras ahlburgi sp. nov. in the shape of the whorl profile, which in S. clavilobum is widest near the umbilicus but in P. ahlburgi sp. nov. widest in the midflank area. Furthermore, S. clavilobum has a conspicuously meandering suture line, while in P. ahlburgi sp. nov. the lobes are acute.

A species similar in conch shape is Stenopharciceras lotzi sp. nov., but this species differs in the suture line. The general outline of the suture line in that species is not meandering as in S. clavilobum , the E 2 lobe is lanceolate and the L and U 2 lobes are usually acute at the base, in contrast to the rounded or blunt lobes in S. clavilobum .

The shape of the whorl profile is also a separating character to distinguish the material from the type region from North African material that has been identified as S. clavilobum ( Petter 1959; Bensaïd 1974; Korn & Klug 2002; Bockwinkel et al. 2009, 2013a, 2015, 2017). As shown in the latter monographic articles, the conch is, in the specimens from the Anti-Atlas, widest in the midflank area, from where the flanks converge towards the umbilicus and the venter. This contrasts with S. clavilobum , where it is widest near the umbilicus.

Figures

Fig. 43. Synpharciceras clavilobum (Sandberger & Sandberger, 1850), holotype 42 (Wiesbaden Museum) from Oberscheld, photograph and reproduction of the figure in Sandberger & Sandberger (1850–1856: pl. 8 figs 3, 3a). Scale bar units = 1 mm.

Fig. 44. Synpharciceras clavilobum (Sandberger & Sandberger, 1850). A. Specimen MB.C.3653 (Lotz 1901 Coll.) from Oberscheld (Gründchesseite Mine). B. Specimen MB.C.22191 (Koch Coll.) from Oberscheld (Anna Mine). Scale bar units = 1 mm.

Fig. 45. Synpharciceras clavilobum (Sandberger & Sandberger, 1850). A. Suture line of holotype 42 (Wiesbaden Museum) from Oberscheld, at ww= 13.8 mm, wh=14.5 mm. B. Suture line of specimen MB.C.3653 (Lotz 1901 Coll.) from Oberscheld (Gründchesseite Mine), at dm= 28.3 mm, ww =15.0 mm, wh= 16.8 mm. C–F. Ontogeneric trajectories of the cardinal conch parameters. Abbreviations: see Material and methods. Scale bar units = 1 mm.

Tables

Table 27. Conch dimensions and ratios of selected specimens of Synpharciceras clavilobum (Sandberger & Sandberger, 1850).

Specimen	dm	ww	wh	uw	ah	ww / dm	ww / wh	uw / dm	WER	IZR
MB.C.3653	33.4	15.7	18.3	0.5	7.9	0.47	0.86	0.01	1.72	0.57
Wiesbaden 42	29.0	13.9	15.0	1.4	–	0.48	0.93	0.05	–	–
MB.C.22191	25.2	13.7	13.4	1.2	6.0	0.54	1.02	0.05	1.72	0.55