Lunupharciceras kochi, 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 : 52-55

Lunupharciceras kochi sp. nov.

urn:lsid:zoobank.org:act:8A30D64E-E259-4EAA-8368-5EAEE216FA9F

Figs 39–40 ; Tables 23–24

Diagnosis

Lunupharciceras with extremely discoidal, evolute conch at 20 mm dm (ww/ dm ~ 0.30; uw/ dm ~0.47) and extremely discoidal, subevolute conch at 40 mm dm (ww / dm ~0.28; uw /dm ~0.42). Whorl profile nearly circular (ww/ wh ~ 1.00) at 20 mm dm and compressed at 40 mm dm (ww/ dm ~ 0.70). WER moderate. Umbilical wall steep, umbilical margin rounded, flanks converging to the continuously rounded venter. Whorl profile in the adult stage with weakly concave outer flanks, pronounced, subangular ventrolateral shoulder and weakly flattened venter. Without or with very weak ventrolateral riblets. Suture line with lanceolate E 2 and L lobes, three outer U lobes, the first and second U-shaped, the third small and asymmertric.

Etymology

Named after Carl Koch (1827–1882), who assembled a large collection of Roteisenstein fossils including the type of the new species.

Material examined

Holotype GERMANY • Rhenish Mountains , Langenaubach (Grube Constanze); late Givetian (Red Ironstone); Koch Coll.; MB.C.3627 . ( Fig. 39A )

Paratypes GERMANY • 3 specimens; Rhenish Mountains , Langenaubach (Grube Constanze); late Givetian (Red Ironstone); Stein Coll.; MB.C.22185 to 22187 • 2 specimens; Rhenish Mountains , Oberscheld (Grube Anna); late Givetian (Red Ironstone); Koch Coll.; MB.C.3628 , MB.C.30252 • 1 specimen; Rhenish Mountains , Dillenburg; late Givetian (Red Ironstone); Kauth Coll.; MB.C.22177 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Neuerburg); late Givetian (Red Ironstone); Emmel 1906 Coll.; MB.C.3611 • 1 specimen; Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); MB.C.7632 • 1 specimen; Rhenish Mountains , Oberscheld , Sessacker; late Givetian (Red Ironstone); Dannenberg Coll.; MB.C.22196 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Königszug); late Givetian (Red Ironstone); Dannenberg Coll.; MB.C.30253 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Prinzkessel, 100 m Sohle); late Givetian (Red Ironstone); Lotz 1902 Coll.; MB.C.22181 .

Description

Five specimens are selected for description and illustration:

Holotype MB.C.3627: incomplete, laterally partly deformed specimen with 83 mm conch diameter in sparitic, iron-rich limestone. It is a steinkern in which the right side is better preserved than the left side, the penultimate whorl shows suture lines. The last half of the terminal volution belongs to the body chamber ( Fig. 39A ).

Paratype MB.C.22186: incomplete specimen with 57 mm conch diameter in haematitic ironstone; about half of the last volution belongs to the body chamber ( Fig. 39B ).

Paratype MB.C.3628: rather well-preserved, fully septate, exfoliated specimen with 50 mm conch diameter in sparitic, iron-rich limestone ( Fig. 39C ).

Paratype MB.C.22177: rather well-preserved, fully septate, largely exfoliated specimen with 27 mm conch diameter in sparitic, iron-rich limestone ( Fig. 39D ).

Paratype MB.C.22181: rather well-preserved steinkern specimen with 24 mm conch diameter preserved haematitic ironstone ( Fig. 39E ).

Holotype MB.C.3627 with 83 mm conch diameter has a conch that is extremely discoidal and subevolute; the whorl profile is compressed and widest near the umbilical shoulder. The coiling rate is moderate, the umbilical wall is shallow and rounded and the flanks converge slowly towards the angular ventrolateral shoulder that delimits the flank from the slightly flattened venter ( Fig. 39A ). The steinkern shows traces of rhythmically strengthened growth lines, producing shallow folds on flanks and venter. These folds are particularly strong on the outer flank. Course of the growth lines is strongly biconvex with a rather high and wide dorsolateral projection, a shallow lateral sinus, and a narrow ventrolateral projection. The inner whorls appear to be smooth, but they are not well-preserved. However, they demonstrate that the conch shape of the juvenile stage is strikingly different from the adult stage, as it is serpenticonic with slowly expanding volutions.

The smaller paratype MB.C.22186 with 57 mm conch diameter shows the transformation from the preadult to the adult stage. It also has an extremely discoidal and subevolute conch with moderate coiling rate; the whorl profile is compressed with steep umbilical wall, rounded umbilical margin, and flattened, slowly converging flanks and narrowly rounded venter. Lamellar, biconvex growth lines are visible ( Fig. 39B ).

Specimen MB.C.22181 with 24 mm conch diameter allows the description of an intermediate growth stage. It has a discoidal and evolute conch; the whorl profile is nearly circular with oblique umbilical wall, flanks and venter broadly rounded ( Fig. 39E ). No traces of ventrolateral spiral grooves are visible.

The suture line of paratype MB.C.3628 has, at 44 mm phragmocone diameter, a general meandering outline with a high median saddle that attains more than 80 % of the external lobe depth ( Fig. 40A ). The prong of the E lobe as well as the shorter lateral lobe are lanceolate and weakly pouched with a pointed base. They are separated by a weakly inflated, narrow ventrolateral saddle. There are three umbilical lobes on the flank; they are much shorter than the lateral lobe. The first two are U-shaped and the third is small and asymmetric.

Remarks

Lunupharciceras lunulicosta has a similar adult conch shape, but differs from L. kochi sp. nov. in its narrower umbilicus. L. lunulicosta is subevolute at 20 mm conch diameter (uw / dm ~ 0.40), while

L. kochi sp. nov. is still evolute (uw /dm ~0.47). At 50 mm conch diameter, the difference is even larger (uw / dm ~ 0.30 in L. lunulicosta but more than 0.40 in L. kochi sp. nov.).

Figures

Fig. 39. Lunupharciceras kochi sp. nov. A. Holotype MB.C.3627 (Koch Coll.) from Langenaubach (Constanze Mine). B. Paratype MB.C.22186 (Stein Coll.) from Langenaubach (Constanze Mine). C. Paratype MB.C.3628 (Koch Coll.) from Oberscheld (Anna Mine). D. Paratype MB.C.22177 (Kauth Coll.) from Dillenburg. E. Paratype MB.C.22181 (Lotz 1902 Coll.) from Oberscheld (Prinzkessel Mine). Scale bar units = 1 mm.

Fig. 40. Lunupharciceras kochi sp. nov. A. Suture line of paratype MB.C.3628 (Koch Coll.) from Oberscheld (Anna Mine), at dm =44.5 mm, ww =13.0 mm, wh =14.3 mm.B–E. Ontogeneric trajectories of the cardinal conch parameters. Abbreviations: see Material and methods. Scale bar units = 1 mm.