Afromaenioceras crassum ( 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 : 23-25

Afromaenioceras crassum ( Bensaïd, 1974)

Fig. 12 ; Table 9

Maenioceras crassum Bensaïd, 1974: 105 , text-fig. 12c 1, c 2, pl. 2 fig. 11, 11a.

Afromaenioceras crassum – Becker et al. 2004: pl. 1 figs 5–6.

non Bensaidites crassus – Korn & Klug 2002: 141, text-fig. 133e, i.

Diagnosis

Species of Afromaenioceras with thickly pachyconic and subinvolute conch at 5 mm dm (ww/dm~ 0.80; uw/dm ~ 0.35); conch thinly pachyconic and subinvolute at 16 mm dm (ww/dm~ 0.65; uw/dm~0.25) with weakly depressed whorl profile (ww/wh~ 1.45) and low coiling rate (WER ~1.60). Whorl profile at 16 mm conch diameter C-shaped with convex, weakly convergent flanks, broadly rounded ventrolateral shoulder and rounded venter. Ventrolateral shoulder with faint spiral groove. Growth lines coarse, strongly biconvex. Suture line with wide external lobe, small, subangular E 2 lobe, inverted U-shaped ventrolateral saddle and U-shaped lateral lobe.

Material examined

Holotype

MOROCCO • Anti-Atlas, Oued Mzerreb ; middle Givetian ; IGPB-Bensaid-22 (illustrated by Bensaïd 1974: pl. 2 fig. 11).

Additional material

MOROCCO • 25 specs; Anti-Atlas, Oued Mzerreb-W ; beds 10/11 (middle Givetian ); Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31965.1 to MB.C.31965.25 • 46 specs; Anti-Atlas, Jebel Ouaoufilal ; middle Givetian ; Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31966.1 to MB.C.31966.46 .

Description

Specimen MB.C.31965.1 is a limonitic internal mould with 15.5 mm conch diameter, which is well preserved on the left side ( Fig. 12A ). The conch is thinly pachyconic and subinvolute (ww/dm = 0.64; uw/dm = 0.26); the umbilicus starts closing at 12 mm conch diameter. The whorl profile is weakly depressed (ww/wh = 1.46) and the coiling rate is low (WER = 1.62). The flanks are broadly convex and the venter is slightly flattened. A faint spiral groove marks the ventrolateral shoulder. Traces of coarse growth lines on the internal mould show a strongly biconvex course. The suture line has a Y-shaped external lobe with stair-shaped flank, and inverted U-shaped ventrolateral saddle and a deep, U-shaped lateral lobe ( Fig. 12D ). Housean pits are present on the outer flank. The last phragmocone volution has only eleven chambers.

Specimen MB.C.31965.2 is a limonitic internal mould with 10 mm conch diameter, which is well-preserved on the left side ( Fig. 12B ). It is a thinly pachyconic, subevolute conch (ww/dm = 0.67; uw/dm = 0.33) with a moderately depressed whorl profile (ww/wh 1.79) and a low coiling rate (WER = 1.65). The ventrolateral shoulder shows a poorly developed spiral groove. The suture line has an external lobe with strongly pouched, divergent flanks and a broad and deep lateral lobe ( Fig. 12E ). The last phragmocone volution has only ten chambers.

Specimen MB.C.31965.3 ss a well-preserved small limonitic internal mould with 5 mm conch diameter ( Fig. 12C ). It is thickly pachyconic and subevolute (ww/dm = 0.81; uw/dm = 0.34) with a strongly depressed whorl profile (ww/wh = 2.11) and a moderately high coiling rate (WER = 1.78). The umbilical wall is steep, flanks and venter are broadly convex. The suture line of the juvenile specimen shows a V-shaped external lobe with gently convex flanks and a wide, broadly rounded lateral lobe ( Fig. 12F ).

Remarks

Afromaenioceras crassum has a stouter and wider umbilicate conch (ww/dm ~ 0.65; ww/wh ~ 1.50; uw/dm ~ 0.25) at 15 mm dm than A. brumale sp. nov. (ww/dm ~ 0.55; ww/wh ~ 1.15; uw/dm ~ 0.20).

Figures

Fig. 12. Afromaenioceras crassum (Bensaïd, 1974) from Oued Mzerreb-W, bed 10/11. A. Specimen MB.C.31965.1. B. Specimen MB.C.31965.2. C. Specimen MB.C.31965.3. D. Specimen MB.C.31965.1; suture line at wh = 6.6 mm. E. Specimen MB.C.31965.2; suture line at wh = 4.5 mm. F. Specimen MB.C.31965.3; suture line at wh = 1.5 mm. Scale bar units = 1 mm.