Maenioceras mzerrebense, 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 : 9-11

Maenioceras mzerrebense sp. nov.

urn:lsid:zoobank.org:act:99A40866-EEC7-4B6C-90DC-E6F00D6C3E8F

Fig. 5 ; Table 2

? Maenioceras aff. terebratum – Aboussalam & Becker 2001: 89, pl. 1 figs 8–9.

Diagnosis

Species of Maenioceras with thinly pachyconic and subinvolute conch at 8 mm dm (ww/dm ~0.65; uw/ dm ~ 0.30); conch thickly discoidal and subinvolute at 13 mm dm (ww/dm~ 0.55; uw/dm~ 0.25) with weakly depressed whorl profile (ww/wh~ 1.15) and moderately high coiling rate (WER ~1.80). Whorl profile at 13 mm conch diameter horseshoe-shaped with convex, weakly convergent flanks, rounded ventrolateral shoulder and convex venter. Ventrolateral shoulder with a very faint spiral groove. Growth lines coarse, lamellar. Suture line with very wide external lobe, very shallow, asymmetrically rounded E 2 lobe, narrowly rounded ventrolateral saddle and blunt, V-shaped lateral lobe.

Etymology

Named after the type locality Oued Mzerreb.

Type material

Holotype

MOROCCO • Anti-Atlas , Oued Mzerreb-W ; bed 6, middle Givetian ; Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31950.1 (illustrated in Fig. 5B ).

Paratypes

MOROCCO • 10 specs; same collection as for holotype; MB.C.31950.2 to MB.C.31950.11 .

Description

Holotype MB.C.31950.1 is a well-preserved limonitic internal mould with parts of the body chamber preserved ( Fig. 5B ). It has, at 10.6 mm conch diameter, a thickly discoidal and subinvolute conch (ww/ dm = 0.53; uw/dm = 0.26) with low coiling rate (WER = 1.67). The whorl profile is weakly depressed (ww/wh = 1.17) with slightly arched flanks that converge towards the narrowly rounded ventrolateral shoulder, which forms a very inconspicuous margin of the rounded venter. The growth lines are impressed as lamellar, strongly biconvex remains on the surface of the internal mould. The last suture line shows, at 3.8 mm whorl height, a very wide external lobe, a very shallow E 2 lobe at the upper flank of the E lobe, a small and low, rounded ventrolateral saddle and a V-shaped lateral lobe with narrowly rounded base. ( Fig. 5E ). The last half volution of the phragmocone has eight septa, of which the last are more closely spaced.

Paratype MB.C.31950.3 is a well-preserved limonitic internal mould of a fully chambered specimen ( Fig. 5C ). It has at 8.4 mm diameter a thinly pachyconic and subinvolute conch (ww/dm = 0.62; uw/ dm = 0.29) with low coiling rate (WER = 1.72). The whorl profile is weakly depressed (ww/wh ~1.36); the flanks are slightly convex and converge towards the rounded ventrolateral shoulder and the rounded venter. The growth lines appear to be coarse, lamellar and strongly biconvex in their course. The last volution of the phragmocone has 12 chambers.

Paratype MB.C.31950.2 is a well-preserved limonitic internal mould ( Fig. 5A ). It has, at 12.6 mm diameter, a thickly discoidal and subinvolute conch (ww/dm = 0.55; uw/dm~ 0.25) and shows that the umbilicus starts closing at about 10 mm conch diameter. The flanks are convex and converge towards the ventrolateral shoulder, which appears to be subangular with a weak ventrolateral groove; the venter is nearly flat.

Remarks

Maenioceras mzerrebense sp. nov. is stouter and more evolute (ww/dm~ 0.55; uw/dm~ 0.25) than M. afroterebratum sp. nov. (ww/dm ~ 0.45; uw/dm~ 0.15) at a conch diameter of 13 mm. It is also much stouter and more widely umbilicate than M. oufranense sp. nov. (ww/dm~ 0.45; uw/dm~0.12).

Figures

Fig. 5. Maenioceras mzerrebense sp. nov. from Oued Mzerreb-W, bed 6. A. Paratype MB.C.31950.2. B. Holotype MB.C.31950.1. C. Paratype MB.C.31950.3. D. Paratype MB.C.31950.4. E. Holotype MB.C.31950.1; suture line at wh = 3.8 mm. F. Paratype MB.C.31950.5; cross section. Scale bar units = 1 mm.