Maenioceras beckeri, Bockwinkel & Korn, 2024

Bockwinkel, Jürgen & Korn, Dieter, 2024, Ammonoids of the Middle Devonian family Maenioceratidae in the Anti-Atlas of Morocco, European Journal of Taxonomy 921 (1), pp. 1-35 : 13-15

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.

Figures

Fig. 7. Maenioceras beckeri sp. nov. from Hassi Nebech.A. Holotype MB.C.31952.1. B. Paratype MB.C.31952.2. C. Holotype MB.C.31952.1; suture line at wh = 6.4 mm. Scale bar units = 1 mm.