Trimaenioceras klugi, 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 : 25-27

Trimaenioceras klugi gen. et sp. nov.

urn:lsid:zoobank.org:act:D659BF7F-C9C9-4150-9CF5-73B94B957BCE

Fig. 13 ; Table 10

Bensaidites n. sp. – Korn & Klug 2002: 141, text-fig. 133h, k.

Maenioceras n. sp. II – Aboussalam & Becker 2011: text-figs 8.3–4.

Diagnosis

Species of Trimaenioceras gen. nov. with thickly discoidal and involute conch at 20 mm dm (ww/ dm ~ 0.50; uw/dm ~ 0.05) with weakly compressed whorl profile (ww/wh ~ 0.95) and low coiling rate (WER ~ 1.55). Whorl profile at 20 mm conch diameter horseshoe-shaped with convex, weakly convergent flanks, rounded ventrolateral shoulder and rounded venter. Ventrolateral shoulder without spiral groove. Growth lines fine. Suture line with very wide external lobe, deep, cuneiform, weakly asymmetric E 2 lobe, symmetrically rounded ventrolateral saddle and V-shaped, slightly asymmetric, acute lateral lobe.

Etymology

Named after Christian Klug, who discovered the ammonoid assemblage.

Type material

Holotype

MOROCCO • Anti-Atlas , Tafilalt , Jebel Ouaoufilal ; middle Givetian ; Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31967.1 (illustrated in Fig. 13A ).

Paratypes

MOROCCO • 241 specs; same collection data as for holotype; MB.C.31967.2 to MB.C.31967.242 • 24 specs; Oued Mzerreb-W ; beds 10/11 (middle Givetian ); Bockwinkel and Ebbighausen 2004 Coll.; MB.C.31968.1 to MB.C.31968.24 .

Description

Holotype MB.C.31967.1 is a well-preserved limonitic internal mould with 19 mm conch diameter ( Fig. 13A ). The conch is thickly discoidal and involute (ww/dm = 0.50; uw/dm = 0.06) with a weakly compressed whorl profile (ww/wh = 0.93) and a low coiling rate (WER = 1.52). The flanks are nearly parallel; the ventrolateral shoulder and the venter are continuously rounded. The last phragmocone volution has 14 chambers.

Paratype MB.C.31967.2 has, at 18.5 mm diameter, a conch with very similar proportions like the holotype ( Fig. 13B ). The suture line has an extremely wide external lobe, which is subdivided in three almost identical prongs. The E 1 lobe is lanceolate and separated from the asymmetric, cuneiform E 2 lobe by a nearly symmetric median saddle that reaches three quarters of the depth of the external lobe. The ventrolateral saddle is inverted U-shaped and nearly symmetric; the lateral lobe is slightly asymmetric V-shaped with convex ventral flank and nearly straight dorsal flank ( Fig. 13E ). The last phragmocone volution has 14 chambers.

Paratypes MB.C.31968.1 (14 mm conch diameter; Fig. 13C ) and MB.C.31967.3 (11 mm conch diameter; Fig. 13D ) show the morphology of the intermediate growth stage, in which the umbilicus is being closed by increasing overlap of the inner flank upon the umbilicus. The suture line of paratype MB.C.31968.1 is similar to that of paratype MB.C.31967.2, but possesses less deep lobes ( Fig. 13F ). The ventrolateral saddle is narrowly rounded. The last phragmocone volution of paratype MB.C.31968.1 has 12 chambers.

Paratype MB.C.31967.4 was sectioned, but shows that the inner whorls are not preserved ( Fig. 13G ). However, it shows clearly that the whorl profile is, at 12 mm conch diameter, horseshoe-shaped. It is widest in the midflank area, from where the flanks converge towards the umbilicus and the continuously rounded venter. The umbilical wall is very low and strongly convex.

Remarks

Trimaenioceras klugi gen. et sp. nov. is similar to T. eculeus gen. et sp. nov., but differs in the more slender and narrowly umbilicate conch in comparative growth stages. At around 15 mm conch diameter, ~ 0. 50 and ~ 0.05 in T. klugi , but ww/dm~0.60 and uw/dm~ 0.25 in T. eculeus .

Figures

Fig. 13. Trimaenioceras klugi gen. et sp. nov. A. Holotype MB.C.31967.1 from Jebel Ouaoufilal. B. Paratype MB.C.31967.2 from Jebel Ouaoufilal. C. Paratype MB.C.31968.1 from Oued Mzerreb-W, beds 10/11. D. Paratype MB.C.31967.3 from Jebel Ouaoufilal. E. Paratype MB.C.31967.2 from Jebel Ouaoufilal; suture line at wh = 6.4 mm. F. Paratype MB.C.31968.1 from Oued Mzerreb-W, beds 10/11; suture line at wh = 6.4 mm. G. Paratype MB.C.31967.4 from Jebel Ouaoufilal; cross section. Scale bar units = 1 mm.