Pharciceras kruegeri, Korn & Bockwinkel, 2021

Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), European Journal of Taxonomy 771, pp. 1-79 : 26-30

Pharciceras kruegeri sp. nov.

urn:lsid:zoobank.org:act:CC6C112F-D0AB-41EE-AE54-45905BD1F6B2

Figs 20–22 ; Tables 10–11

Diagnosis

Species of Pharciceras with thinly pachyconic, subevolute conch at 30 mm dm (ww / dm ~ 0.62; uw/ dm ~ 0.35); thinly discoidal, subinvolute at 60 mm dm (ww/ dm ~ 0.40; uw / dm ~ 0.28). Whorl profile depressed at 30 mm dm (ww / wh ~1.55) and rounded-triangular at 60 mm dm (ww /wh ~ 1.00); whorl expansion rate low to moderate. Preadult and adult stages with broadly convex flanks, strongly converging to the narrowly rounded venter. Growth lines coarse, strongly biconvex; ventrolateral shoulder with two faint spiral grooves. Outer suture line with symmetric, lanceolate prongs of the external lobe, a U-shaped lateral lobe, a small V-shaped U 2 lobe and a shallow and wide U 4 lobe.

Etymology

Named after the teacher Krüger (Hagen), who provided an important collection of fossils from the Red Ironstone.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); Krüger 1873 Coll.; MB.C.22170 . ( Fig. 20A )

Paratypes GERMANY • 1 specimen; Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); Krüger 1873 Coll.; MB.C.22162 • 1 specimen; Rhenish Mountains , Oberscheld (Tiefe Grube); late Givetian (Red Ironstone); Etzold 1910 Coll.; MB.C.3654 • 1 specimen; Rhenish Mountains , Langenaubach (Grube Constanze); late Givetian (Red Ironstone); Koch Coll.; MB.C.22163 • 1 specimen; Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); Dannenberg Coll.; MB.C.22198 • 1 specimen; Rhenish Mountains , Weilburg (Grube Georg-Joseph); late Givetian (Red Ironstone); Menk 1914 Coll.; MB.C.30236 • 1 specimen; Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); SMF.Mbg.6359 .

Description

Five specimens are selected for description and illustration:

Holotype MB.C.22170: laterally deformed, incomplete specimen with 65 mm conch diameter in haematitic ironstone; the last volution belongs almost completely to the body chamber ( Fig. 20A ).

Paratype SMF.Mbg.6359: laterally strongly deformed specimen with 94 mm conch diameter in haematitic ironstone; the last volution belongs almost completely to the body chamber ( Fig. 21 ).

Paratype MB.C.22162: incomplete, weakly deformed specimen with total 75 mm diameter in haematitic, micritic limestone; conch dimensions can be obtained at 54 mm diameter ( Fig. 20B ).

Paratype MB.C.22163: strongly deformed, moderately preserved specimen with 74 mm conch diameter in ironstone ( Fig. 20C ).

Paratype MB.C.3654: slightly deformed, well-preserved steinkern specimen with 32 mm conch diameter filled with sparry calcite. Nearly the entire last volution belongs to the body chamber ( Fig. 20D ).

Holotype MB.C.22170 and paratype MB.C.22162 are, at 65 and 54 mm conch diameter, similar in their proportions and represent the adult stage of the species ( Fig. 20A–B ). In this stage, the conch is discoidal and subinvolute with moderate coiling rate; the whorl profile rounded triangular with steep umbilical wall, rounded umbilical margin and strongly converging flanks. The evenly rounded venter is separated from the flanks by two shallow spiral grooves. Both specimens possess ornament with lamellar, biconvex growth lines.

The smaller paratype MB.C.3654 with 32 mm conch diameter ( Fig. 20D ) is attributed to this species because it shows a conch geometry that is present in the earlier whorls of the two larger individuals. The conch is thinly pachyconic and subevolute; the whorl profile is depressed with rather steep umbilical wall and broadly rounded flanks and venter. Two very shallow spiral grooves are visible on the ventrolateral shoulder on both sides. Only some shell remains are preserved, they indicate coarse biconvex growth lines with a very high and narrow ventrolateral projection, which has a position at the spiral grooves. The suture line has, at a conch diameter of about 22 mm, a very wide external lobe with subparallel flanks and two V-shaped lobes on the flank, of which the outer (lateral lobe) has the size of the prongs of the external lobe, and the inner one (U 2 lobe) is small ( Fig. 22A ), the U 4 lobe is shallow and wide.

The large paratype SMF.Mbg.6359 with 94 mm diameter shows that the conch proportions change towards a more slender conch geometry with a narrower venter. The specimen shows that the longitudinal grooves are still present in this stage ( Fig. 21 ).

Remarks

Among the species from the Red Ironstone, Pharciceras kayseri is most similar but differs in the slenderer conch (ww/ dm ~0.30; ww / wh ~ 0.65) from P. kruegeri sp. nov. (ww /dm ~ 0.40; ww / wh ~ 1.05) at 60 mm diameter. The ornament consists of very delicate growth lines in P. kayseri but coarse growth lines in P. kruegeri sp. nov.

The wide conch with the rounded-triangular whorl profile makes it rather easy to separate P. kruegeri sp. nov. from the other species of Pharciceras .

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Figures

Fig. 20. Pharciceras kruegeri sp. nov. A. Holotype MB.C.22170 (Krüger 1873 Coll.) from Oberscheld. B. Paratype MB.C.22162 (Krüger 1873 Coll.) from Oberscheld. C. Paratype MB.C.22163 (Koch Coll.) from Langenaubach (Constanze Mine). D. Paratype MB.C.3654 (Etzold 1910 Coll.) from Oberscheld (‘Tiefe Grube’). Scale bar units = 1 mm.

Fig. 21. Pharciceras kruegeri sp. nov., large paratype SMF.Mbg.6359 from Oberscheld. Scale bar units = 1 mm.

Fig. 22. Pharciceras kruegeri sp. nov. A. Suture line of paratype MB.C.3654 (Etzold 1910 Coll.) from Oberscheld (‘Tiefe Grube’), at dm=20 mm, ww =15.5 mm, wh= 6.5 mm. B–E. Ontogeneric trajectories of the cardinal conch parameters. Abbreviations: see Material and methods. Scale bar units = 1 mm.