Afromaenioceras bensaidi, 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 : 19-21

Afromaenioceras bensaidi sp. nov.

urn:lsid:zoobank.org:act:5066DF05-35BC-424A-A3C1-AD7598BD3405

Fig. 10 ; Table 7

Afromaenioceras n. sp. – Aboussalam & Becker 2011: text-fig. 8.5–6.

Diagnosis

Species of Afromaenioceras with thinly pachyconic and subinvolute conch at 10 mm dm (ww/dm~ 0.60; uw/dm ~ 0.20); conch thickly discoidal and involute at 22 mm dm (ww/dm ~0.45; uw/dm ~0.05) with moderately compressed whorl profile (ww/wh~ 0.85) and moderately high coiling rate (WER~ 1.85). Whorl profile at 22 mm conch diameter horseshoe-shaped with convex, weakly convergent flanks, broadly rounded ventrolateral shoulder and flattened venter. Ventrolateral shoulder with faint or pronounced spiral groove. Growth lines coarse, bundled, strongly biconvex. Suture line with wide external lobe, small, subangular E 2 lobe, inverted U-shaped ventrolateral saddle and asymmetric, tongue-shaped lateral lobe.

Etymology

Named after Mohamed Bensaïd, to honour his contribution to Moroccan palaeontology.

Type material

Holotype

MOROCCO • Anti-Atlas , Oued Mzerreb-W ; beds 10/11 (middle Givetian); Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31959.1 (illustrated in Fig. 10A ).

Paratypes

MOROCCO • 10 specs; same collection data as for holotype; MB.C.31959.2 to MB.C.31959.11 .

Description

Holotype MB.C.31959.1 is a moderately well-preserved, somewhat corroded specimen with 22 mm conch diameter ( Fig. 10A ). The conch is thinly discoidal and involute (ww/dm = 0.46; uw/dm = 0.06); the whorl profile is weakly compressed (ww/wh = 0.86) and the coiling rate moderately high (WER = 1.83). The flanks are slightly convex and terminated by a striking spiral groove on the ventrolateral shoulder; the venter is flattened. The internal mould shows traces of coarse, lamellar growth lines with strongly biconvex course. The suture line is not well-preserved, but possesses a wide external lobe with stair-shaped flanks, a high asymmetrically rounded ventrolateral saddle and a deep, asymmetrically rounded lateral lobe.

Paratypes MB.C.31959.4 ( Fig. 10B ) and MB.C.31959.2 ( Fig. 10C ) are thinly pachyconic, involute conchs with 10 mm dm (ww/dm~0.60; uw/dm~ 0.20) with a weakly depressed whorl profile (ww/ wh~ 1.25) and a moderate coiling rate. Paratype MB.C.31959.2 shows the typical Afromaenioceras suture line with a Y-shaped external lobe with stair-shaped flanks, an asymmetrically rounded, inverted U-shaped ventrolateral saddle and a deep, asymmetrically rounded lateral lobe ( Fig. 10E ).

Paratype MB.C.31959.3 is an internal mould with a conch diameter of 9.5 mm ( Fig. 10D ). The conch is thinly pachyconic and subinvolute (ww/dm = 0.62; uw/dm = 0.17) with a weakly depressed whorl profile (ww/wh = 1.29) and a low coiling rate (WER = 1.70). The flanks are convex and the venter broadly rounded.

Paratype MB.C.31959.5 was sectioned and shows the ontogenetic development of the conch geometry between diameters of 4.5 and 10 mm ( Fig. 10F ). Three volutions can be studied; they show only minor ontogenetic changes in the shape of the whorl profiles. A trend toward a more slender conch with a narrower umbilicus can be observed. During this growth interval, the whorl profile changes from crescent-shaped to C-shaped.

Remarks

Afromaenioceras bensaidi sp. nov. is characterised by the involute conch in the adult stage and is thus clearly separate from the other species of the genus.

Figures

Fig. 10. Afromaenioceras bensaidi sp. nov. from Oued Mzerreb-W, beds 10/11. A. Holotype MB.C.31959.1. B. Paratype MB.C.31959.4. C. Paratype MB.C.31959.2. D. Paratype MB.C.31959.3. E. Paratype MB.C.31959.2; suture line at wh = 5.2 mm. F. Paratype MB.C.31959.5; cross section. Scale bar units = 1 mm.