Trimaenioceras eculeus Bockwinkel & Korn 2024, gen. et sp. nov.
Creators: name: Bockwinkel, Jürgen
name: Korn, Dieter
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Agoniatitida
Maenioceratidae
Trimaenioceras
Trimaenioceras eculeus

description: Trimaenioceras eculeus gen. et sp. nov.
urn:lsid:zoobank.org:act: 9EBD0D9B-BFCE-4218-B3DA-A78113DF0399
Fig. 14; Table 11
Diagnosis
Species of Trimaenioceras gen. nov. with thickly discoidal and subinvolute conch at 15 mm dm (ww/ dm ~ 0.60; uw/dm ~ 0.25); conch thinly discoidal and subinvolute at 28 mm dm (ww/dm ~ 0.40; uw/ dm ~ 0.10) with weakly compressed whorl profile (ww/wh ~ 0.85) and low coiling rate (WER ~ 1.65). Whorl profile at 28 mm conch diameter horseshoe-shaped with convex, weakly convergent 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, strongly asymmetric E 2 lobe, rounded ventrolateral saddle and V-shaped, symmetric, acute lateral lobe.
Etymology
From the Latin nomen ‘ eculeus ’ = ‘a little horse’, because of the horseshoe-shaped whorl profile.
Type material
Holotype
MOROCCO • Anti-Atlas, south-eastern Tafilalt, Hassi Nebech, section 2; middle Givetian; Bockwinkel and Ebbighausen 2002–2004 Coll.; MB.C.31969.1 (illustrated in Fig. 14A).
Paratypes
MOROCCO • 27 specs; same collection data as for holotype; MB.C.31969.2 to MB.C.31969.28 • 5 specs; same collection data as for holotype except collected by locals; MB.C.31970.1 to MB.C.31970.5.
Description
Holotype MB.C.31969.1 is a well-preserved limonitic, fully chambered specimen with 28 mm conch diameter (Fig. 14A). It is thinly discoidal and involute (ww/dm = 0.41; uw/dm = 0.11) and shows that the umbilicus starts closing at about 25 mm conch diameter by overlap of the flanks. The whorl profile is weakly compressed (ww/wh = 0.84) and the coiling rate is low (WER = 1.64). The suture line shows a very wide external lobe that is subdivided into three parts, of which the E 1 lobe is wider and deeper than the asymmetric, cuneiform E 2 lobes. The median saddle reaches about two thirds of the depth of the external lobe. The ventrolateral saddle is nearly symmetric and rounded; the lateral lobe is V-shaped with gently convex flanks (Fig. 14D). The last phragmocone volution has 16 chambers.
Paratypes MB.C.31969.2 (20.5 mm conch diameter; Fig. 14B) and MB.C.31969.3 (15 mm conch diameter; Fig. 14C) demonstrate the ontogenetic transformation of the conch shape. Together with the holotype, they show that the conch width decreases, between 15 and 28 mm conch diameter, from a ww/ dm ratio of about 0.60 to about 0.40; parallel to this, the uw/dm ratio decreases from 0.25 to about 0.10. The last phragmocone volution of paratype MB.C.31969.2 has 13 chambers.
The suture line of paratype MB.C.31969.4 shows, at a whorl height of 9.5 mm, a very wide external lobe; the E 2 lobe is nearly V-shaped and blunt. The ventrolateral saddle is inverted U-shaped and the lateral lobe is V-shaped with a convex ventral flank (Fig. 14E).
Remarks
Trimaenioceras eculeus gen. et sp. nov. is similar to T. klugi gen. et sp. nov., but differs in the stouter and more widely umbilicate conch in comparative growth stages. At around 15 mm conch diameter, ww/ dm ~ 0.60 and uw/dm~ 0.25 in T. eculeus, but ~ 0. 50 and ~ 0.05 in T. klugi.
description: Published as part of Bockwinkel, Jürgen & Korn, Dieter, 2024, Ammonoids of the Middle Devonian family Maenioceratidae in the Anti-Atlas of Morocco, pp. 1-35 in European Journal of Taxonomy 921 (1) on pages 27-29, DOI: 10.5852/ejt.2024.921.2413, http://zenodo.org/record/10590243