Goniatites spirifer Roemer, 1850

Goniatites spirifer Roemer, 1850 View in CoL

Figs 12–13 View Fig View Fig ; Tables 6–7 View Table 6 View Table 7 , A 3 View Table 3

Goniatites spirifer Roemer, 1850: 51 View in CoL , pl. 8 fig. 16.

Goniatites striatus View in CoL – Delépine 1941: 67, pl. 5 figs 1–2.

Glyphioceras striatum spirifer – Kobold 1933: 489, pl. 22 figs 5–6.

Goniatites spirifer View in CoL – Korn 1988: 93, pl. 23 figs 3 – 4, pl. 59 figs 5 – 6; 1990: 33, pl. 11 figs 1–10, pl. 12 figs 9–11, text-fig. 12a–b; 1997: 50, pl. 4 figs 10–11. — Gischler & Korn 1992: 282, text-figs 4g, 6c – d, 7a.

non Goniatites striatus spirifer View in CoL – Nicolaus 1963: 107, pl. 1 fig. 6, pl. 2 figs 2–4, pl. 4 figs 8–11, pl. 5 figs 8–10.

Diagnosis

Species of Goniatites reaching a conch diameter of 80 mm. Conch thickly globular at 10 mm diameter (ww/dm ~ 1.00), thickly pachyconic at 30 mm diameter (ww/dm ~ 0.80) and thinly pachyconic at 50 mm diameter (ww/dm ~ 0.70). Umbilicus very narrow at 10 mm dm (uw/dm ~ 0.05), in the adult stage slightly opening; umbilical wall rounded. Coiling rate in the adult stage low (WER ~ 1.50). Ornamentation with spiral lines that are coarser than the growth lines, which are rursiradiate and biconvex with moderate dorsolateral projection and lower ventrolateral projection; external sinus shallow. Suture line with a Y-shaped, moderately narrow external lobe (0.60 of the external lobe depth, 1.20 of the adventive lobe width) and a moderately high median saddle (0.45 of the external lobe depth). Flanks of the external lobe weakly sinuous, ventrolateral saddle acute, adventive lobe V-shaped with convex flanks.

Type material

Holotype

GERMANY – Harz Mountains • Lautenthal ,without more precise information;“ Posidonomyenschiefer ” ( Late Viséan ); Roemer Coll.; GPIC Nr. 389 ; illustrated by Roemer (1850: pl. 6 fig. 16) and Gischler & Korn (1992: text-fig. 7a).

Material examined

GERMANY – Harz Mountains • 2 specs; Winterberg quarry near Bad Grund ; dyke fillings of the Goniatites spirifer Zone ( Late Viséan ); 2015; Knappe leg.; MB.C. 32222.1 , MB.C. 32222.2 .

MOROCCO – Central Meseta • 5 specs; Sidi Lamine , sample 4; Goniatites spirifer Zone ( Late Viséan ); 2007; Korn and Ebbighausen leg.; MB.C. 32208.1 to MB.C. 32208.5 . – Jerada Basin • 13 specs; OujdaBerguent road, 4 km south of the junction with the road to Jerada ; Goniatites spirifer Zone ( Late Viséan ); 2007; Korn and Ebbighausen leg.; MB.C. 32220.1 to MB.C. 32220.13 .

Description

Specimen MB.C.32208.1 ( Fig. 12A View Fig ) is an incomplete, partly crushed conch about 70 mm in diameter, with a fairly well-preserved shell ornament. The ornamentation consists of spiral lines, with around 90 visible between the centre of the venter and the umbilical margin. The spiral lines are typically evenly spaced and slightly narrower than the gaps between them. Very fine granulation appears at the intersections with the much finer biconvex growth lines.

Specimen MB.C.32208.2 ( Fig. 12B View Fig ) is an incomplete, deformed internal mould with a diameter of about 65 mm. The shell ornament is partially preserved, though some of it has been imprinted onto the internal mould. Four constrictions of the internal mould are clearly visible at 90-degree intervals. These constrictions run in a concave arc across the flanks and tend to form a ventral projection.

Specimen MB.C.32220.1 ( Fig. 12C View Fig ) is an internal mould of a specimen with a conch diameter of 47 mm. It is thinly pachyconic and involute (ww/dm = 0.69; uw/dm = 0.12), with a very low coiling rate (WER = 1.46). The whorl profile shows a broad venter and nearly subparallel flanks, with a rounded umbilical margin. The body chamber spans at least one complete volution and displays three constrictions, each with a low, wide dorsolateral projection that extends almost straight across the outer flank and venter. The shell ornament is impressed on the internal mould, consisting of fine spiral lines that are nearly as wide as the spaces between them.

The cross sections of the comparative specimens MB.C.32222.1 ( Fig. 13A View Fig ) and MB.C.32222.2 ( Fig. 13B View Fig ) from Bad Grund in the Harz Mountains provide valuable insights into the ontogenetic development of conch geometry, which is not possible for the Moroccan specimens. Both specimens display almost identical conch geometry and ontogeny, reflected in parallel ontogenetic trajectories ( Fig. 13C–E View Fig ). The whorl profile is C-shaped in all stages beyond 2 mm conch diameter, but the ww/dm ratio decreases steadily from 1.20 to 0.80 as the conch diameter increases from 2 to 48 mm. Simultaneously, the ww/ wh ratio drops from 2.60 to 1.60.

The ontogenetic trajectory of the coiling rate exhibits noticeable oscillation. An early ontogenetic stage with a low coiling rate (WER = 1.60) up to 2 mm shell diameter is followed by an accelerated coiling rate, reaching about 1.90 between 5 and 7 mm diameter, before decreasing again to approximately 1.50 between 30 and 50 mm diameter.

Remarks

Specimens of Goniatites spirifer from Sidi Lamine were previously illustrated by Delépine (1941: pl. 5 figs 1–2) under the name “ Goniatites striatus ”. These show a preservation state very similar to the newly collected material.

Goniatites spirifer is a common species in the Rhenish Mountains ( Korn 1988, 1990), though reports of well-preserved three-dimensional specimens are rare. As a result, the species has occasionally been misinterpreted, as in the case of Nicolaus (1963), who incorrectly attributed stratigraphically older forms to G. spirifer .