Maenioceras ornatum Korn & Bockwinkel 2021, sp. nov.
Creators: name: Korn, Dieter
name: Bockwinkel, Jürgen
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Ammonoidea
Maenioceratidae
Maenioceras
Maenioceras ornatum

description: Maenioceras ornatum sp. nov.
urn:lsid:zoobank.org:act: D40EFEA4-C79A-4A01-A3AD-4DDB2AF923C5
Figs 6–7; Table 2
Maeneceras terebratum – Holzapfel 1895: 107, pl. 4 figs 14, 18, pl. 6 figs 6–7, 9 (only). — Foord & Crick 1897: 123, text-fig. 57. — Frech 1897: pl. 32a fig. 17a–b; 1902: 54, text-fig. 15. — Wedekind 1918: 114, pl. 16 fig. 7, text-fig. 23a.
Maenioceras terebratum – Walliser 1970: 121, pl. 2 figs 1–2, text-fig. 5d. — House 1971: 28, pl. 2 fig. 5. — Walliser et al. 1995: 111, text-fig. 6d. — Korn & Klug 2002: text-figs 132, 133a.
Diagnosis
Maenioceras with thinly discoidal, involute conch at 25 mm dm (ww / dm ~0.45; uw/ dm ~0.05). Whorl profile slightly compressed (ww / wh ~ 0.90); flanks flattened and nearly parallel, venter broadly rounded. Growth lines coarse, lamellar, strongly biconvex; ventrolateral shoulder with a distinct spiral groove.
Etymology
Named after the Latin ‘ ornatum ’, meaning ‘decorated’, because of the shell ornament.
Material examined
Holotype GERMANY • Rhenish Mountains, Oberscheld (possibly Caroline Mine); middle Givetian (Red Ironstone); MB.C.30229.1. (Fig. 6C)
Paratypes GERMANY • 13 specimens; Rhenish Mountains, Oberscheld (possibly Caroline Mine); middle Givetian (Red Ironstone); MB.C.30229.2 to MB.C.30229.14 • 1 specimen; Rhenish Mountains, Oberscheld (Caroline Mine, 128 m level); middle Givetian (Red Ironstone); Möbus Coll.; MB.C.30230.
Description
The description is based on three specimens:
Holotype MB.C.30229.1: weakly deformed, comparatively well-preserved specimen with 23 mm conch diameter in red ironstone (Fig. 6C).
Paratype MB.C.30229.2: laterally deformed, incomplete, rather poorly preserved specimen with about 35 mm conch diameter in red ironstone (Fig. 6A).
Paratype MB.C.30229.3: laterally deformed, rather poorly preserved specimen with about 25 mm conch diameter in red ironstone (Fig. 6B).
The three type specimens listed above allow the study of conch geometry and ornament between 20 and 35 mm conch diameter. They show thinly discoidal conchs with parallel flanks; the whorl profile is widest near the midflank, from where the flanks slowly converge towards the umbilicus and a little faster towards the venter. Flanks and venter are separated by a narrowly rounded shoulder that is accompanied, on the flank side, by a shallow longitudinal groove.
Particularly in the holotype MB.C.30229.1, the ornament is well-preserved and shows lamellar growth lines with a broadly rounded dorsolateral projection, a slightly narrower lateral sinus, a very high and narrow ventrolateral projection and a very deep, narrow ventral sinus. Remains of the wrinkle-layer are preserved in the dorsal whorl area; they show very delicate lines.
Remarks
The new species was previously described by Holzapfel (1895) from well-preserved material from the Roteisenstein from Adorf (Fig. 7A). The large specimen illustrated by Holzapfel agrees very well with the specimens from Oberscheld in terms of conch form and ornament. Holzapfel already recognized the differences between the specimens from the Stringocephalus Limestone of Villmar (M. terebratum) and from the Roteisenstein of Oberscheld (M. ornatum sp. nov.) in the strength of the growth lines. However, he considered both forms to belong to M. terebratum.
The new species differs from Maenioceras terebratum in the stouter conch (ww /dm = 0.40–0.45 in M. ornatum sp. nov. at 30 mm conch diameter but 0.25–0.30 in M. terebratum), the wider and slightly flattened venter and the much coarser ornament with lamellar growth lines.
description: Published as part of Korn, Dieter & Bockwinkel, Jürgen, 2021, The pharciceratid ammonoids from the Roteisenstein Formation of Dillenburg (Cephalopoda, Ammonoidea), pp. 1-79 in European Journal of Taxonomy 771 on pages 9-11, DOI: 10.5852/ejt.2021.771.1503, http://zenodo.org/record/5536097