Afromaenioceras sulcatostriatum ( Bensaïd, 1974 )

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 : 15-17

Afromaenioceras sulcatostriatum ( Bensaïd, 1974)

Fig. 8 ; Table 5

Maenioceras sulcatostriatum Bensaïd, 1974: 105 , pl. 2 figs 2–3, 6, 8–9, text-fig. 13.

Maenioceras (Afromaenioceras) sulcatostriatum – Göddertz 1987: 179, pl. 12 figs 10–12, pl. 13 fig 2, fig 1?, text-figs 27b, 28f–k.

Afromaenioceras sulcatostriatum – Korn & Klug 2002: 140, text-fig. 133b.

Diagnosis

Species of Afromaenioceras with thinly pachyconic and subevolute conch at 7 mm dm (ww/dm~ 0.60; uw/dm~ 0.40); conch thickly discoidal and subinvolute at 12 mm dm (ww/dm~0.50; uw/dm~0.30) with weakly depressed whorl profile (ww/wh ~ 1.15) and low coiling rate (WER ~1.65). Whorl profile at 12 mm conch diameter C-shaped with convex, weakly convergent flanks, broadly rounded ventrolateral shoulder and broadly rounded venter. Ventrolateral shoulder with more or less deep spiral groove. Growth lines pronounced, bundled, forming nodes at the ventrolateral shoulder. Suture line with wide external lobe, incipient, subangular E 2 lobe, inverted U-shaped ventrolateral saddle and semicircular lateral lobe.

Type material

Holotype

MOROCCO • Anti-Atlas, Oufrane ; middle Givetian ; IGPB-Bensaid-15 (illustrated by Bensaïd 1974: pl. 2 fig. 3).

Additional material

MOROCCO • 19 specs; Anti-Atlas , Oufrane-E ; bed 10 (middle Givetian); Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31953.1 to MB.C.31953.19 • 5 spec; Anti-Atlas , Oufrane-E ; bed 11 (middle Givetian); Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31954.1 to MB.C.31954.5 • 2 specs; Anti-Atlas , Oufrane-E ; beds 14/15 (middle Givetian); Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31955.1 , MB.C.31955.2 .

Description

Specimen MB.C.31953.1 is a partially corroded but otherwise rather well-preserved limonitic internal mould with 12.2 mm conch diameter ( Fig. 8A ). The conch is thickly discoidal and subinvolute (ww/ dm = 0.52; uw/dm = 0.30) with a low coiling rate (WER = 1.65); the whorl profile is weakly depressed (ww/wh = 1.15). The internal mould shows traces of pronounced, partly bundled growth lines, which produce faint tubercles at the ventrolateral shoulder. On the last volution, there are 13 constrictions of the internal mould; these extend with a low dorsolateral projection, a shallow lateral sinus, an extremely high, subacute ventrolateral projection and a very deep and narrow ventral sinus. These constrictions are deepest in the outer flank area. The specimen possesses a long body chamber and therefore, the suture line not visible.

Specimen MB.C.31953.2 is a well-preserved limonitic internal mould with 8 mm conch diameter, of which half of the last volution belong to the body chamber ( Fig. 8C ). The conch is thickly discoidal and subevolute (ww/dm = 0.54; uw/dm = 0.36) with a low coiling rate (WER = 1.71); the whorl profile is weakly depressed (ww/wh = 1.38). Traces of the growth lines shows that these are bundled at the umbilical margin and that they extend with a strongly biconvex course.

Specimens MB.C.31955.2 (8 mm conch diameter; Fig, 8D) and MB.C.31955.1 (11 mm conch diameter; Fig. 8B ) show somewhat weaker indications of growth lines and weaker constrictions of the internal mould when compared with the specimens MB.C.31953.1 and MB.C.31953.2, but agree in the general conch ratios.

Specimen MB.C.31953.3 was used for the production of a cross section ( Fig. 8F ), in which three volutions up to a conch diameter of nearly 11 mm can be studied. The cross section shows that the ontogenetic changes in the shape of the whorl profiles do not significantly change between 3.5 and 11 mm conch diameter; there is a trend toward a more slender conch with a narrower umbilicus. During this growth interval, the whorl profile changes from crescent-shaped to C-shaped.

The suture line of the specimen MB.C.31954.1 shows, at 3 mm whorl height, a wide external lobe with parallel flanks in its upper half ( Fig. 8E ); the stair-shaped E 2 lobe has a position on the flanks of the external lobe. The ventrolateral saddle is asymmetrically rounded and the lateral lobe is U-shaped and slightly asymmetric. The lateral lobe has only one third of the depth of the external lobe.

Remarks

Afromaenioceras sulcatostriatum is more involute and more slender than A. hiemale sp. nov.

Figures

Fig. 8. Afromaenioceras sulcatostriatum (Bensaïd, 1974) from Oufrane-E. A. Specimen MB.C.31953.1, bed 10. B. Specimen MB.C.31955.1, bed 14/15. C. Specimen MB.C.31953.2, bed 10. D. Specimen MB.C.31955.2, bed 14/15. E. Specimen MB.C.31954.1, bed 11; suture line at wh = 3.0 mm. F. Specimen MB.C.31953.3, bed 10; cross section. Scale bar units = 1 mm.