Maenioceras beckeri Bockwinkel & Korn 2024, sp. nov.
Creators: name: Bockwinkel, Jürgen
name: Korn, Dieter
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Agoniatitida
Maenioceratidae
Maenioceras
Maenioceras beckeri

description: Maenioceras beckeri sp. nov.
urn:lsid:zoobank.org:act: 48EAD7CA-D85E-40E0-B32C-7A6C5A078A7C
Fig. 7; Table 4
Maenioceras excavatum – Petter 1959: 124, pl. 6 fig. 11.
? Maenioceras cf. excavatum – Petter 1959: 125, pl. 6 fig. 13. — Bensaïd 1974: pl. 2 fig. 5.
? Maenioceras n. sp. III – Becker et al. 2004: pl. 1 figs 11–12.
Diagnosis
Species of Maenioceras with thickly discoidal and subinvolute conch at 17 mm dm (ww/dm ~0.50; uw/dm ~ 0.30) with weakly depressed whorl profile (ww/wh ~ 1.20) and low coiling rate (WER~ 1.55). Whorl profile at 17 mm conch diameter horseshoe-shaped with flattened, nearly parallel, weakly convergent flanks, subangular ventrolateral shoulder and broad, nearly flat venter. Ventrolateral shoulder with a faint groove in adult specimens. Growth lines coarse, strongly biconvex. Suture line with extremely wide external lobe, deep, U-shaped E 2 lobe, inverted U-shaped ventrolateral saddle and blunt, tongue-shaped lateral lobe.
Etymology
Named after R. Thomas Becker, who possibly already recognised this species as new.
Type material
Holotype
MOROCCO • Anti-Atlas, Hassi Nebech, section 2; middle Givetian; Bockwinkel and Ebbighausen Coll.; MB.C.31952.1 (illustrated in Fig. 7A).
Paratypes
MOROCCO • 2 specs; same collection data as for holotype; MB.C.31952.2, MB.C.31952.3.
Description
Holotype MB.C.31952.1 is a limonitic internal mould of a fully chambered specimen (Fig, 7A) with 17 mm conch diameter; it is rather well-preserved only on the right side. The conch is thickly discoidal and subinvolute (ww/dm = 0.49; uw/dm = 0.24) with low coiling rate (WER = 1.57). The whorl profile is weakly depressed (ww/wh = 1.18) with slightly convex flanks. The ventrolateral shoulder forms a rather distinct margin separating the flanks and the almost flat, but slightly convex venter. The growth lines are bundled with a strongly biconvex course. The suture line is somewhat unusual for Maenioceras with an extremely wide external lobe and a symmetrically rounded E 2 lobe that is half as deep as the E 1 lobe. On the flank follow a narrowly rounded asymmetrical ventrolateral saddle and a deep, tongue-shaped lateral lobe (Fig, 7C).
Paratype MB.C.31952.2 shows the same conch proportions as the holotype with a ww/dm ratio of 0.49 and an estimated uw/dm ratio of 0.30 at 15 mm dm. Numerous dense growth lines are visible in this specimen (Fig, 7B).
Paratype MB.C.31952.3 is, with a ww/dm ratio of 0.45 and a uw/dm ratio of 0.36 at 14.5 mm conch diameter, slightly more slender and more evolute than the other two type specimens.
Remarks
The deep E 2 lobe in Maenioceras beckeri sp. nov. is the cardinal character to separate the new species from the other species of the genus, which possess a shallow E 2 lobe.
description: Published as part of Bockwinkel, Jürgen & Korn, Dieter, 2024, Ammonoids of the Middle Devonian family Maenioceratidae in the Anti-Atlas of Morocco, pp. 1-35 in European Journal of Taxonomy 921 (1) on pages 13-15, DOI: 10.5852/ejt.2024.921.2413, http://zenodo.org/record/10590243