Ponticeras aequabile ( Beyrich, 1837 )

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 : 21-25

Ponticeras aequabile ( Beyrich, 1837)

Figs 4D , 8–10

Ammonites aequabilis Beyrich, 1837: 34 , pl. 2 fig. 1.

Gephyroceras Kayseri Wedekind, 1918: 123 , 167, pl. 21 fig. 13, text-fig. 28d.

Goniatites aequbilis – Roemer 1843: 34, pl. 9 fig. 14. — Sandberger & Sandberger 1850 –1856: 94, pl. 8 fig. 11.

Gephyroceras aequabile – Wedekind 1918: 123, 167, pl. 21 figs 5–6, text-fig. 28c.

Ponticeras aequabile – Matern 1931: 85. — Schindewolf 1969: 47, text-fig. 7a. — House in House & Ziegler 1977: 77, pl. 1 fig. 25. — Korn & Klug 2002: 98.

Ponticeras barroisi – House in House & Ziegler 1977: 78, pl. 1 figs 1–2.

Ponticeras kayseri – House in House & Ziegler 1977: 78, pl. 1 figs 3–4, 11–12.

? Probeloceras aequabile – Clausen 1969: 150, pl. 24 fig. 7, text-fig. 18h, h1–h3.

non Gephyroceras aequabile var. nov. – Wedekind 1913: 70, pl. 6 fig. 14, text-fig. 14b.

Diagnosis

Species of Ponticeras reaching about 120 mm conch diameter with extremely discoidal, subevolute conch between 40 and 60 mm dm (ww/dm = 0.20–0.25; uw/dm = 0.40–0.45); coiling rate low (WER = 1.70–1.75). Whorl profile weakly compressed (ww/wh = 0.65–0.75); umbilical wall oblique and flattened, venter narrowly rounded. Growth lines very fine, strongly biconvex. Flanks often with a spiral ridge on the outer side of the umbilicus parallel to the umbilical seam. Suture line with V-shaped external lobe; median saddle moderately high, E 2 lobe small, pointed, ventrolateral saddle and lateral lobe asymmetrically rounded.

Material examined

Lectotype GERMANY • Rhenish Mountains , Oberscheld (Sessacker); late Givetian (Red Ironstone); Beyrich 1835 Coll.; MB.C.4289.1 . Illustrated here in Fig. 8D .

Paralectotypes GERMANY • 1 specimen; Rhenish Mountains , Oberscheld (Sessacker); late Givetian (Red Ironstone); Beyrich 1835 Coll.; MB.C.30425 • 1 specimen; Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); Beyrich 1835 Coll.; MB.C.5600 .

Additional material

GERMANY • 1 specimen; Rhenish Mountains , Dillenburg; late Givetian (Red Ironstone); Erbreich Coll.; MB.C.4293 • 1 specimen; Rhenish Mountains , Dillenburg; late Givetian (Red Ironstone); MB.C.30419 • 1 specimen; Rhenish Mountains , Nanzenbach (Grube Königszug); late Givetian (Red Ironstone); Dannenberg Coll.; MB.C.30420 • 2 specimens; Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); Erbreich Coll.; MB.C.4289.2 , MB.C.5576 • 3 specimens; Rhenish Mountains , Oberscheld ; late Givetian (Red Ironstone); Kauth Coll.; MB.C.4290 , MB.C.30421.1 , MB.C.30421.2 • 1 specimen; Rhenish Mountains , Oberscheld; late Givetian (Red Ironstone); Liebe Coll.; MB.C.30422 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Königszug); late Givetian (Red Ironstone); Jung 1902 Coll.; MB.C.30423 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Volpertseiche); late Givetian (Red Ironstone); Kauth Coll.; MB.C.30424 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Volpertseiche); late Givetian (Red Ironstone); Koch Coll.; MB.C.4291 • 1 specimen; Rhenish Mountains , Oberscheld (Sessacker); late Givetian (Red Ironstone); Dannenberg Coll.; MB.C.30426 • 1 specimen; Rhenish Mountains , Oberscheld (Staatliche Grube); late Givetian (Red Ironstone); Hubach 1920 Coll.; MB.C.4300 • 1 specimen; Rhenish Mountains , Oberscheld (Grube Königszug); late Givetian (Red Ironstone); Meuhsen 1855 Coll.; SMF.Mbg.2324 • 1 specimen; Rhenish Mountains , Langenaubach; late Givetian (Red Ironstone); GZG 389-82 .

Description

Nine specimens are selected for description and illustration:

Holotype MB.C.4289.1: rather poorly preserved, worn specimen with 43 mm conch diameter in haematitic ironstone. Shell ornament barely visible ( Fig. 8D ).

MB.C.4291: fully septate, incomplete but rather well-preserved specimen with 61 mm conch diameter in haematitic limestone, phragmocone filled with white calcite ( Fig. 8A ).

MB.C.4290: rather well-preserved specimen with 50 mm conch diameter in haematitic ironstone; fully covered with shell ( Fig. 8B ).

MB.C.4289.2: moderately preserved specimen with 42 mm diameter in haematitic ironstone, phragmocone filled with white calcite ( Fig. 8E ).

MB.C.5576: incomplete specimen with 45 mm diameter in haematitic limestone; shell surface wellvisible ( Fig. 8C ).

MB.C.30421.1: rather well-preserved, laterally deformed specimen with 36 mm conch diameter in reddish-ochre limestone; almost fully covered with shell.

MB.C.30419: sectioned specimen with 60 mm conch diameter in haematitic limestone ( Fig. 9A ).

Specimen SMF.Mbg.2324, the holotype of “ Gephyroceras Kayseri ”, is a specimen with 58 mm diameter ( Fig. 4C ).

Specimen GZG 389-82, the invalid neotype of Ponticeras aequabile , is an incomplete specimen with about 105 mm conch diameter in haematitic limestone ( Fig. 10 ).

The material allows the study of conch geometry between 36 and 105 mm conch diameter. Only slight changes in proportions can be recognised in this growth interval ( Fig. 9A ). The conch is always extremely discoidal and subevolute to evolute (ww/dm = 0.20–0.25; uw/dm = 0.39–0.47) with a weak tendency towards a wider umbilicus at a larger diameter. The whorl profile of the sectioned specimen MB.C.30419

is always compressed (ww/wh = 0.64–0.70) with a broadly rounded or slightly flattened and oblique umbilical wall, a rounded umbilical margin, strongly converging flanks and a narrowly rounded venter. Rarely, as in specimen MB.C.4290, there is a weak depression visible in the ventrolateral area ( Fig. 8B ).

The ornament is preserved in several specimens. In specimen MB.C.4290 the shell is decorated with irregular coarse growth lines with a strongly biconvex course; the dorsolateral projection is low, the ventrolateral projection is very high and narrow and the ventral sinus is narrow and very deep. Specimen MB.C.4291 shows three faint spiral lines in the middle flank area ( Fig. 8A ).

Several of the specimens, such as MB.C.4291, possess a spiral ridge, of approximately 0.5 mm width, on the midflank parallel to the umbilical seem of the next volution. In specimen MB.C.4290, such a ridge is only developed on the right side.

Remarks

House in House & Ziegler (1977: 77: pl. 1 fig. 25) stated that the original specimen could not be traced and proposed a neotype from the Göttingen Collection (GZG 389-82), which was figured by Wedekind (1918: pl. 21 fig. 6). However, specimen MB.C.4289.1 (Beyrich 1835 Coll.) is stored in the MfN collection; it was figured by Beyrich (1837: pl. 2 fig. 1) and is re-illustrated here in Fig. 8D . As there were other specimens in the Beyrich collection, it is designated the lectotype here.

Wedekind (1913) regarded specimens with a weakly applanate venter as belonging to P. aequabile var. nov. In a later paper, Wedekind (1918) introduced the new species “ Gephyroceras Kayseri ” ( Fig. 4D ) that is characterised by a narrow, blunt venter but clearly shows the morphology of the lectotype of P. aequabile .

Ponticeras aequabile differs from P. materni sp. nov., which also occurs in the Oberscheld assemblages, in the narrowly rounded venter, which is flattened in the latter species.

Ponticeras aequabile is also distinguished from the other species of the genus by the closely rounded venter, which is either broadly rounded ( P. lebedeffi , P. uralicum , P altaicum , P. uchtense , P. discoidale ), flattened ( P. auritum ) or separated from the flanks by ventrolateral longitudinal grooves ( P. tschernyschewi , P. domanicense , P. keyserlingi , P. regale ).

Figures

Fig. 4. Specimens of Pseudoprobeloceras Bensaïd, 1974 and Ponticeras Matern, 1929; reproductions from Wedekind (1918). A. Pseudoprobeloceras pernai (Wedekind, 1918), lectotype SMF.Mbg.2322 (Welsch 1912 Coll.) from Oberscheld (Prinzkessel Mine). B. Pseudoprobeloceras applanatum (Wedekind, 1918), holotype SMF.Mbg.2323 (Welsch Coll.) from Oberscheld (Prinzkessel Mine). C. Pseudoprobeloceras pernai (Wedekind, 1918), holotype SMF.Mbg.2326 (Welsch 1913 Coll.) of “Gephyroceras Barroisi” from Oberscheld (Prinzkessel Mine). D. Ponticeras aequabile (Beyrich, 1837), holotype SMF.Mbg.2324 (Meuhsen 1855 Coll.) of “Gephyroceras Kayseri” from Oberscheld (Königszug Mine). Scale bar units = 1 mm.

Fig. 8. Ponticeras aequabile (Beyrich, 1837). A. Specimen MB.C.4291 (Koch Coll.) from Oberscheld. B. Specimen MB.C.4290 (Kauth Coll.) from Oberscheld. C. Specimen MB.C.5576 (Erbreich Coll.) from Oberscheld. D. Lectotype MB.C.4289.1 (Beyrich 1835 Coll.) from Oberscheld (Sessacker). E. Specimen MB.C.4289.2 (Erbreich Coll.) from Oberscheld. Scale bar units = 1 mm.

Fig. 9. Ponticeras aequabile (Beyrich, 1837). A. Cross section of specimen MB.C.30419 from the Dillenburg area. B. Suture line of lectotype MB.C.4289.1 (Beyrich 1835 Coll.) from Oberscheld (Sessacker), at dm = 31.5 mm, wh = 10.0 mm. C–F. Ontogenetic trajectories of the cardinal conch parameters. Scale bar units = 1 mm.

Fig. 10. Ponticeras aequabile (Beyrich, 1837); specimen GZG 389-82 from Langenaubach; the specimen erroneously proposed as neotype by House in House & Ziegler (1977). Scale bar units = 1 mm.