Afromaenioceras hiemale, 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 : 17-19

Afromaenioceras hiemale sp. nov.

urn:lsid:zoobank.org:act:6D5CA601-FB40-471A-9A07-34526CBE4CD6

Fig. 9 ; Table 6

Diagnosis

Species of Afromaenioceras with thickly pachyconic and subevolute conch at 6 mm dm (ww/dm~ 0.75; uw/dm ~ 0.45); conch thinly pachyconic and subevolute at 16 mm dm (ww/dm~ 0.65; uw/dm~0.40) with moderately depressed whorl profile (ww/wh ~ 1.90) and low coiling rate (WER ~ 1.55). Whorl profile at 16 mm conch diameter C-shaped with convex, weakly convergent flanks, broadly rounded ventrolateral shoulder and flattened venter. Ventrolateral shoulder without 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 U-shaped lateral lobe.

Etymology

After the Latin adjective ‘ hiemalis, - e ’ = ‘winterly’; the conch resembles a winter tire.

Type material

Holotype

MOROCCO • Anti-Atlas , Tafilalt , Jebel Ouaoufilal ; middle Givetian ; Bockwinkel and Ebbighausen 2002–2004 Coll.; MB.C.31956.1 (illustrated in Fig. 9A ).

Paratypes

MOROCCO • 25 specs; same collection data as for holotype; MB.C.31956.2 to MB.C.31956.26 • 1 spec.; Anti-Atlas , Oufrane-W ; bed 11 (middle Givetian ); Bockwinkel and Ebbighausen 2002–2004 Coll.; MB.C.31957 • 1 spec.; Anti-Atlas , Oued Mzerreb-W ; bed 11 (middle Givetian ); Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31958 .

Description

Holotype MB.C.31956.1 is a limonitic internal mould with 16 mm conch diameter, of which the left side well-preserved and the right side is somewhat corroded ( Fig. 9A ). The conch is thinly pachyconic and subevolute (ww/dm = 0.64; uw/dm = 0.39) with a low coiling rate (WER = 1.57); the umbilicus starts closing at 14 mm diameter. The whorl profile is moderately depressed (ww/wh = 1.88) with broadly rounded flanks and a nearly flat venter. The internal mould shows riblet-like traces of bundled growth lines, which extend with a strongly biconvex course; they form small tubercles at the umbilical margin. The suture line has a Y-shaped external lobe with stair-shaped flanks, a rectangular and blunt E 2 lobe, a slightly asymmetric, inverted U-shaped ventrolateral saddle and a deep, broadly rounded U-shaped lateral lobe ( Fig. 9D ). On the outer flank and the ventrolateral region occurs, on both sides of the conch, a sequence of densely arranged Housean pits (compare De Baets et al. 2011). The last phragmocone volution has only eleven chambers.

Paratype MB.C.31957 is a well-preserved internal mould with nearly 10 mm conch diameter ( Fig. 9B ). The conch is thickly pachyconic and subevolute (ww/dm = 0.73; uw/dm = 0.40); the whorl profile is strongly depressed (ww/wh = 2.22) and the coiling rate is moderate (WER = 1.72). The internal mould shows traces of riblets and weak constrictions with strongly biconvex course.

Paratype MB.C.31956.2 is a well-preserved small internal mould with 6 mm conch diameter ( Fig. 9C ). It is thickly pachyconic and evolute (ww/dm = 0.76; uw/dm = 0.45) with a strongly depressed whorl profile (ww/wh = 2.46) and a low coiling rate (WER = 1.65). The internal mould shows traces of riblets with strongly biconvex course. The suture line has a V-shaped, unsubdivided external lobe with slightly curved flanks and a shallow, broadly rounded lateral lobe ( Fig. 9E ).

Remarks

The conch of Afromaenioceras hiemale sp. nov. is, with a ww/dm ratio of about 0.65 and a uw/dm ratio of about 0.40 at 16 mm conch diameter, significantly stouter and more evolute than the conch of A. sulcatostriatum with the ratios ww/dm~ 0.50 and uw/dm~ 0.30 at 12 mm conch diameter.

Figures

Fig. 9. Afromaenioceras hiemale sp. nov. A. Holotype MB.C.31956.1 from Jebel Ouaoufilal. B. Paratype MB.C.31957 from Oufrane. C. Paratype MB.C.31956.2 from Jebel Ouaoufilal. D. Holotype MB.C.31956.1 from Jebel Ouaoufilal; suture line at wh = 4.5. E. Paratype MB.C.31956.2 from Jebel Ouaoufilal; suture line at wh =1.6 mm. Scale bar units = 1 mm.