Acanthoclymenia forcipifera (Sandberger & Sandberger, 1851)

Korn, Dieter & Bockwinkel, Jürgen, 2022, The early gephuroceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 823, pp. 10-47 : 40-42

Acanthoclymenia forcipifera (Sandberger & Sandberger, 1851)

Figs 19–20

Goniatites forcipifer Sandberger & Sandberger, 1851: 81 , pl. 6 fig. 3.

Gephyroceras forcipiferum – Wedekind 1913: 51; 1918: 122, text-fig. 28f.

Ponticeras forcipiferum – Matern 1931: 84.

Probeloceras forcipiferum – House in House & Ziegler 1977: 80, pl. 3 figs 28–29.

Acanthoclymenia forcipifer – Korn & Klug 2002: 119, text-fig. 123d.

Acanthoclymenia genundewa – Dzik 2002: text-fig. 50f–i.

non Probeloceras forcipiferum – Petter 1959: 155, pl. 11 figs 11–12, text-fig. 40e. — Ruan 1981: 42, pl. 9 figs 1–5, 8, text-fig. 16.

Diagnosis

Species of Acanthoclymenia reaching about 40 mm conch diameter with extremely discoidal, subinvolute conch between 12 and 28 mm dm (ww/dm = 0.20–0.25; uw/dm ~ 0.28); coiling rate very high (WER increasing from 2.25 to 2.60). Whorl profile strongly compressed (ww/wh ~ 0.50); umbilical wall shallow and rounded, whorl profile pear-shaped, ventrolateral margin angular, venter flat or slightly concave. Growth lines very fine, strongly biconvex.

Material examined

Lectotype GERMANY • Rhenish Mountains, Oberscheld ; early Frasnian (Red Ironstone); Wiesb. 36a. Illustrated by Sandberger & Sandberger (1850 –1856: pl. 6 fig. 3), re-illustrated by House in House & Ziegler (1977: pl. 3 figs 28–29) and here ( Fig. 19 ).

Additional material

GERMANY • 1 specimen; Rhenish Mountains , Oberscheld (Eiserne Hand, Betagrube); early Frasnian (Red Ironstone); Trempel Coll.; MB.C.30432 • 1 specimen; Rhenish Mountains , Oberscheld (Eiserne Hand, Grube Friedrich); early Frasnian (Red Ironstone); Kegel Coll.; MB.C.3669 • 9 specimens; Rhenish Mountains , Oberscheld ( Grube Anna ); early Frasnian (Red Ironstone); Koch Coll.; MB.C.22199.1 , MB.C.22199.2 , MB.C.22199.3 , MB.C.22200 , MB.C.30433.1 , MB.C.30433.2 , MB.C.30433.3 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Sahlgrund, 205 m-Sohle); early Frasnian (Red Ironstone); MB.C.30434 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Stillingseisenzug); early Frasnian (Red Ironstone); Möbus 1901 Coll.; MB.C.30435 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Ypsilanta); early Frasnian (Red Ironstone); Etzold 1910 Coll.; MB.C.30436 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Ypsilanta); early Frasnian (Red Ironstone); Lotz 1901–1902 Coll.; MB.C.30437 .

Description

Six specimens are selected for description and illustration:

Lectotype Wiesb. 36a: fully septate specimen with 16 mm conch diameter in haematitic ironstone ( Fig. 19 ).

MB.C.22199.1: rather well-preserved specimen with 28 mm conch diameter in haematitic iron ore; largely covered with shell ( Fig. 20A ).

MB.C.22199.2: well-preserved, slightly deformed specimen with 14 mm conch diameter in haematitic iron ore; largely covered with shell ( Fig. 20D ).

MB.C.30433.1: well-preserved, slightly deformed specimen with 27 mm conch diameter in haematitic iron ore; largely covered with shell ( Fig. 20B ).

MB.C.30433.2: well-preserved, slightly deformed specimen with 22 mm conch diameter in haematitic iron ore; largely covered with shell ( Fig. 20C ).

MB.C.30433.3: fragmentary specimen co-occurring in a block of haematitic iron ore together with a specimen Crickites Wedekind, 1913 .

The specimens MB.C.22199.2 (14 mm dm), MB.C.30433.2 (22 mm dm), MB.C.30433.1 (27 mm dm) and MB.C.22199.1 (28 mm dm) show that, during this growth interval, no significant changes in the conch proportions can be recognised ( Fig. 20 ). The conchs are extremely discoidal and subinvolute with very high coiling rate; the whorl profile is compressed. The umbilical wall is very shallow; the flanks converge towards the angular ventrolateral shoulder, the outer flanks are weakly incurved and the venter is flat. The ornament consists of fine growth lines with biconvex course; they extend with a very low dorsolateral projection on the umbilical margin and a high and narrow ventrolateral projection across the flanks. Faint short riblets are present around the umbilicus.

Remarks

When Sandberger & Sandberger (1850 –1856) described the new species Goniatites forcipifer , they did not make it clear whether the species name (“carrying a fire tong”) was a noun or an adjective. Since such species names are usually considered adjectives, we here decline it to the feminine form.

Acanthoclymenia forcipifera differs from the second species of the genus from Oberscheld, A. planorbis (Sandberger & Sandberger, 1851) , in the much narrower umbilicus at 12 mm conch diameter (uw/dm ~ 0.30 in A. forcipifera but ~ 0.50 in A. planorbis ).

Figures

Fig. 19. Acanthoclymenia forcipifera (Sandberger & Sandberger, 1851); lectotype 36a in the Wiesbaden collection from Oberscheld; photograph, dorsal reconstruction and reproduction of the figure of Sandberger & Sandberger (1850–1856: pl. 6 fig. 3, 3a). Scale bar units = 1 mm.

Fig. 20. Acanthoclymenia forcipifera (Sandberger & Sandberger, 1851), all Koch Coll from Oberscheld (Anna Mine). A. Specimen MB.C.22199.1. B. Specimen MB.C.30433.1. C. Specimen MB.C.30433.2. D. Specimen MB.C.22199.2. Scale bar units = 1 mm.