Stenopharciceras lotzi, 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 : 56-58

Stenopharciceras lotzi sp. nov.

urn:lsid:zoobank.org:act:88748636-7B2F-4BC3-850E-9A42BE35A9DF

Figs 41–42 ; Tables 25–26

Diagnosis

Stenopharciceras with thickly discoidal conch at 20 mm dm (ww / dm ~ 0.50) and thinly discoidal conch at 40 mm dm (ww/ dm ~0.40); with very narrow to closed umbilicus. Whorl profile slightly compressed (ww / wh ~ 0.95) at 20 mm dm and more strongly compressed at 40 mm dm (ww / dm ~0.75); conch widest in the midflank area. Flanks and venter continuously rounded. Outer suture line with bell- or funnel-shaped E 1 lobe, parallel-sided, usually pointed, E 2, L and U 2 lobes separated by rounded saddles. Inner flank and umbilical wall with blunt or rounded U 4, U 6, U 8 and U 10 lobes.

Etymology

Named after the geologist Heinrich Lotz (1873–1943), who provided an important collection of fossils from the Red Ironstone.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld (Grube Prinzkessel); late Givetian (Red Ironstone); Lotz 1901 Coll.; MB.C.30254 ; illustrated in Fig. 41C .

Paratypes GERMANY • 1 specimen; Rhenish Mountains , Oberscheld (Grube Königszug, 90 m Sohle); late Givetian (Red Ironstone); Lotz 1902 Coll.; MB.C.30255 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Prinzkessel); late Givetian (Red Ironstone); Lotz 1901 Coll.; MB.C.30256 • 3 specimens; Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); MB.C.2280 , MB.C.30257 , MB.C.30258 .

Description

Four specimens are selected for description and illustration:

Paratype MB.C.2280: rather well-preserved specimen with nearly 40 mm conch diameter in haematitic ironstone ( Fig. 41A ).

Paratype MB.C.30255: deformed specimen with 35 mm conch diameter in haematitic ironstone ( Fig. 41B ).

Holotype MB.C.30254: deformed specimen with 27 mm conch diameter in haematitic ironstone ( Fig. 41C ).

Paratype MB.C.30256: fully chambered, deformed specimen with 23 mm conch diameter in haematitic ironstone; some parts of the shell preserved ( Fig. 41D ).

The material allows the study of a rather short ontogentic interval between about 20 and 40 mm conch diameter. During this interval, the conch becomes slenderer (ww/dm decreases from 0.55 to 0.40; ww / wh decreases from 1.00 to 0.70). The flanks are convex and the venter is continuously rounded. Specimens MB.C.30254 and MB.C.2280 show a shell ornament with fine, widely spaced growth lines that extend with a lateral sinus and a high, linguiform ventrolateral salient across the flanks.

The suture line of the specimens closely resemble each others. They show that, between 22 and 35 mm conch diameter, the shape of the external lobe is rather stable, but that this lobe becomes more dominant in its size during ontogeny ( Fig. 42A–D ). While in holotype MB.C.30254, at 22 mm conch diameter, the lateral lobe is almost as deep as the external lobe, this proportion has shifted towards a much shorter L lobe in specimen MB.C.30255 at 35 mm diameter. The shape of the lateral lobe changes from lanceolate in holotype MB.C.30254 to tongue-shaped in paratype MB.C.30255. The E 1 lobe is bell-shaped in MB.C.30255 but V-shaped in the smaller specimens MB.C.30254 or MB.C.2280

Remarks

Stenopharciceras lotzi sp. nov. superficially resembles Pluripharciceras ahlburgi sp. nov. but possesses a stouter conch (ww / dm ~0.40 at 35 mm dm in contrast to 0.35 in P. ahlburgi sp. nov.). The main differences are in the suture line; S. lotzi sp. nov. possesses fewer, rounded lobes on the flank while these lobes are V-shaped in P. ahlburgi sp. nov.

Stenopharciceras lotzi sp. nov. differs from Synpharciceras clavilobum , which it closely resembles in conch shape, in the suture line which is not meandering as in S. clavilobum in the general outline. Furthermore, 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 .

Figures

Fig. 41. Stenopharciceras lotzi sp. nov. A. Paratype MB.C.2280 from Oberscheld. B. Paratype MB.C.30255 (Lotz 1902 Coll.) from Oberscheld (Königszug Mine). C. Holotype MB.C.30254 (Lotz 1901 Coll.) from Oberscheld (Prinzkessel Mine). D. Paratype MB.C.30256 (Lotz 1902 Coll.) from Oberscheld (Anna Mine). Scale bar units = 1 mm.

Fig. 42. Stenopharciceras lotzi sp. nov. A. Suture line of holotype MB.C.30254 (Lotz 1901 Coll.) from Oberscheld (Prinzkessel Mine), at dm =22.2 mm, ww = 9.9 mm, wh =10.6 mm. B. Suture line of paratype MB.C.30256 (Lotz 1901 Coll.) from Oberscheld (Prinzkessel Mine), at dm =22.8 mm, ww =10.1 mm, wh =11.2 mm.C. Suture line of paratype MB.C.2280 from Oberscheld, at ww =12.6 mm, wh= 14.7 mm. D. Suture line of paratype MB.C.30255 (Lotz 1901 Coll.) from Oberscheld (Königszug Mine), at dm =35.0 mm, ww =13.5 mm, wh =19.5 mm. E–H. Ontogeneric trajectories of the cardinal conch parameters. Abbreviations: see Material and methods. Scale bar units = 1 mm.