Pluripharciceras ahlburgi, 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 : 62-66

Pluripharciceras ahlburgi sp. nov.

urn:lsid:zoobank.org:act:A582D7F8-2FDE-4A6A-BE12-D45E39487A06

Figs 46–48 ; Tables 28–29

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

Diagnosis

Pluripharciceras with thinly discoidal conch at 20 mm dm (ww/ dm ~0.40) and extremely discoidal conch at 40 mm dm (ww/ dm ~0.30); with very narrow to closed umbilicus. Whorl profile slightly compressed (ww / wh ~ 0.90) at 20 mm dm and weakly compressed at 40 mm dm (ww /dm ~0.60); conch widest in the midflank area. WER moderate to high. Flanks and venter continuously rounded; venter narrowly rounded. Outer suture line with parallel-sided, usually pointed, E 2, L and U 2 lobes meandering with separating saddles. Inner flank and umbilical wall with acute U 4, U 6, U 8 and U 10 lobes.

Etymology

Named after Johannes Ahlburg (1883–1919), who assembled a collection of Roteisenstein fossils including the type of the new species.

Material examined

Holotype GERMANY • Rhenish Mountains , Oberscheld (Westfeld der Grube Königszug, Firste der 120–150 m Sohle); late Givetian (Red Ironstone); Ahlburg Coll.; MB.C.3644 . ( Fig. 46B )

Paratypes GERMANY • 12 specimens; Rhenish Mountains , Oberscheld (Westfeld der Grube Königszug, Firste der 120–150 m Sohle); late Givetian (Red Ironstone); Ahlburg Coll.; MB.C.3625 , MB.C.3632 , MB.C.3640 , MB.C.3659 to 3661 , MB.C.30265.1 to 30265.6 • 3 specimens; Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); Jung 1902, Lotz 1901–1902 Coll.; MB.C.3639 , MB.C.22155 , MB.C.22188 • 1 specimen; Rhenish Mountains , Oberscheld (Tiefe Grube); late Givetian (Red Ironstone); SMF.Mbg.2319 • 1 specimen; Rhenish Mountains , Oberscheld (Tiefe Grube); late Givetian (Red Ironstone); Etzold 1910 Coll.; MB.C.22179 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Neuerburg); late Givetian (Red Ironstone); Kauth Coll.; MB.C.30262 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Königszug, 90 m Sohle); late Givetian (Red Ironstone); Teese 1902 Coll.; MB.C.30263 • 2 specimens; Rhenish Mountains , Oberscheld (Grube Königszug, 60 m Sohle); late Givetian (Red Ironstone); Lotz 1901, Jung 1901 Coll.; MB.C.493 , MB.C.30264 .

Description

Nine specimens are selected for description and illustration:

Paratype SMF.Mbg.2319: rather well-preserved specimen with 75 mm conch diameter in red ironstone; the specimen was figured by Wedekind (1918, pl. 20. fig. 4) ( Fig. 48 ).

Paratype MB.C.493: rather well-preserved specimen with 35 mm conch diameter, showing shell ornament, on a block of haematitic ironstone ( Fig. 46A ).

Holotype MB.C.3644: fairly well-preserved specimen with 52 mm conch diameter in red ironstone; approximately half of the last preserved volution belongs to the body chamber ( Fig. 46B ).

Paratype MB.C.3639: steinkern specimen with 51 mm conch diameter in iron-rich micritic limestone ( Fig. 46C ).

Paratype MB.C.3640: rather well-preserved specimen with 41 mm conch diameter in iron-rich micritic limestone ( Fig. 46D ).

MB.C.3659: deformed but rather well-preserved specimen with 35 mm conch diameter in iron-rich micritic limestone ( Fig. 46E ).

Paratype MB.C.22155: laterally deformed specimen with 36 mm conch diameter in haematitic ironstone ( Fig. 46F ).

Paratype MB.C.3632: laterally deformed specimen with 29 mm conch diameter in iron-rich micritic limestone ( Fig. 46G ).

Paratype MB.C.22179: sectioned specimen with 21 mm conch diameter in red ironstone ( Fig. 47A ).

The ontogeny of the principal conch parameters shows triphasic and biphasic trajectories ( Fig. 47 D–G ). The ww / dm trajectory is triphasic with a short early juvenile phase (ww/ dm decreasing from 0.50 at 1 mm dm to 0.45 at 2 mm dm), a short second phase (ww/ dm increasing from 0.45 at 2 mm dm to 0.55 at 8 mm dm) and a longer third phase with decrease of the ww / dm ratio from 0.55 to 0.25 at 75 mm conch diameter. The uw/ dm trajectory has a biphasic course with a short first phase (increase of the uw/ dm ratio to 0.45 at 3 mm dm) and a second phase with a discontinuous decrease eventually closing the umbilicus.

The whorl profile is crescent-shaped in the juvenile stage up to about 10 mm conch diameter; thereafter the whorls increase rapidly in height. At the same time, the widest point of the conch migrates from the umbilicus to the midflank area. Specimens larger than 20 mm show a very shallow umbilical wall. The venter becomes continuously narrower during ontogeny; above 60 mm conch diameter it is very narrowly rounded or subacute.

Remains of the shell ornament are visible in several specimens. The growth lines are very fine and in paratype MB.C.493, they extend with a moderately deep lateral sinus and a prominent, narrow ventrolateral salient across the flanks. Runzelschicht is preserved in a number of specimens.

In specimen MB.C.3644, some parts of the suture line are visible, showing six acute lobes on the middle and inner flank.

Remarks

Pluripharciceras ahlburgi sp. nov. differs from Synpharciceras clavilobum in the shape of the whorl profile, which in P. ahlburgi sp. nov. is widest in the midflank area but in S. clavilobum is widest near the umbilicus. Furthermore, S. clavilobum has a conspicuously meandering suture line, while in P. ahlburgi sp. nov. the lobes are V-shaped and acute.

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

Figures

Fig. 46. Pluripharciceras ahlburgi sp. nov. A. Paratype MB.C.493 (Lotz 1901 Coll.) from Oberscheld (Königszug Mine). B. Holotype MB.C.3644 (Ahlburg Coll.) from Oberscheld (Königszug Mine). C. Paratype MB.C.3639 from Oberscheld. D. Paratype MB.C.3640 (Ahlburg Coll.) from Oberscheld (Königszug Mine). E. Paratype MB.C.3659 (Ahlburg Coll.) from Oberscheld (Königszug Mine). F. Paratype MB.C.22155 (Jung 1902 Coll.) from Oberscheld. G. Paratype MB.C.3632 (Ahlburg Coll.) from Oberscheld (Königszug Mine). Scale bar units = 1 mm.

Fig. 47. Pluripharciceras ahlburgi sp. nov. A. Cross section of paratype MB.C.22179 (Etzold 1910 Coll.) from Oberscheld (Tiefe Grube), at dm =22.2 mm, ww =9.9 mm, wh =10.6 mm. B. Suture line of holotype MB.C.3644 (Ahlburg Coll.) from Oberscheld (Königszug Mine), at ww = 10.0 mm, wh= 16.0 mm.C. Suture line of paratype MB.C.3639 from Oberscheld, at ww =12.0 mm, wh=20.5 mm. D–G. Ontogeneric trajectories of the cardinal conch parameters. Abbreviations: see Material and methods. Scale bar units = 1 mm.

Fig. 48. Pluripharciceras ahlburgi sp. nov, paratype SMF.Mbg.2319 from Oberscheld (Tiefe Grube), reproduction from Wedekind (1918: pl. 20 fig. 4). Scale bar units = 1 mm.