Trimaenioceras fuscina, 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 : 30-31

Trimaenioceras fuscina gen. et sp. nov.

urn:lsid:zoobank.org:act:C5B0E733-6BD9-48EB-A89A-009451C83B6F

Fig. 15 ; Table 12

Diagnosis

Species of Trimaenioceras gen. nov. with thinly discoidal and subinvolute conch at 20 mm dm (ww/dm ~ 0.40; uw/dm ~ 0.15) with weakly compressed whorl profile (ww/wh ~ 0.85) and low coiling rate (WER ~ 1.70). Whorl profile at 20 mm conch diameter horseshoe-shaped with flattened subparallel flanks, rounded ventrolateral shoulder and rounded venter. Ventrolateral shoulder without spiral groove. Growth lines very fine. Suture line with wide external lobe, moderately deep, cuneiform E 2 lobe, rounded ventrolateral saddle and V-shaped, acute lateral lobe.

Etymology

After the Latin nomen ‘ fuscina ’ = ‘trident’, because of the shape of the external lobe.

Type material

Holotype

MOROCCO • Anti-Atlas , south-eastern Tafilalt , Hassi Nebech , section 2; middle Givetian ; Bockwinkel and Ebbighausen 2002–2004 Coll.; MB.C.31970.1 (illustrated in Fig. 14B ).

Paratype

MOROCCO • 1 spec.; same collection data as for holotype; MB.C.31970.2 (illustrated in Fig. 14A ).

Description

Holotype MB.C.31970.1 is a fully septate internal mould of a specimen with 21 mm conch diameter ( Fig. 15B ). The conch is thinly discoidal with a rather small umbilicus (ww/dm = 0.42; uw/dm = 0.15); a weakly compressed whorl profile (ww/wh = 0.89) and a low coiling rate (WER = 1.71). The specimen shows that the umbilicus is being narrowed, caused by increased overlap of the flanks upon the umbilicus, during the last preserved volution.

Paratype MB.C.31970.2 is a specimen with 21.5 mm conch diameter ( Fig. 15A ), which in size and proportions of the conch closely resembles the holotype (ww/dm = 0.40; uw/dm = 0.14). The suture line shows a very wide external lobe that is subdivided into three almost equally wide and deep prongs, of which the E 2 lobes are asymmetric and cuneiform. The median saddle reaches about two thirds of the depth of the external lobe. The ventrolateral saddle is nearly symmetric and inclined towards the venter; the lateral lobe is V-shaped with gently convex flanks ( Fig. 15C ). The last phragmocone volution has about 16 chambers.

Remarks

Trimaenioceras fuscina gen. et sp. nov. is the species of the genus with the most slender conch. At about 20 mm conch diameter, its ww/dm ratio is ~0.40, while it is~ 0.50 in T. klugi gen. et sp. nov. and T. eculeus gen. et sp. nov. Trimaenioceras fuscina differs from T. klugi in the less deep sutural elements of the external lobe. A suture line very similar to T. fuscina can be seen in T. eculeus , but this species differs in the wider umbilicus (uw/dm~ 0.20) at 20 mm conch diameter (uw/dm is only ~ 0.15 in T. fuscina ).

Figures

Fig. 15. Trimaenioceras fuscina gen. et sp. nov. from Jebel Ouaoufilal. A. Paratype MB.C.31970.2. B. Holotype MB.C.31970.1. C. Paratype MB.C.31970.2; suture line at wh = 9.5 mm. Scale bar units = 1 mm.

Fig. 14. Trimaenioceras eculeus gen. et sp. nov., from Hassi Nebech. A. Holotype MB.C.31969.1. B. Paratype MB.C.31969.2. C. Paratype MB.C.31969.3. D. Holotype MB.C.31969.1; suture line at wh = 13.5 mm. E. Paratype MB.C.31969.4; suture line at wh = 9.5 mm. F. Paratype JB HN 1; cross section. Scale bar units = 1 mm.