Pericyclus mercatorius, Korn & Bockwinkel & Ebbighausen & Klug, 2003

Korn, Dieter, Bockwinkel, Jürgen, Ebbighausen, Volker & Klug, Christian, 2003, Palaeobiogeographic and evolutionary meaning of an early Late Tournaisian ammonoid fauna from the Tafilalt of Morocco, Acta Palaeontologica Polonica 48 (1), pp. 71-92 : 85-86

Pericyclus mercatorius sp. nov.

Figs. 23E, F, 25 , 26 .

Derivation of name: After mercatura (Lat. merchandise), because of the origin of the material.

Holotype: Specimen MB.C.3962 (coll. Klug), Fig. 23E.

Type locality and horizon: Taouz, Jebel Ouaoufilal, locality B east of Ksar Bouhamed (Tafilalt, Morocco); Oued Znaïgui Formation, early Late Tournaisian.

Material.— 6 specimens (between 5 and 15 mm diameter) and thus rare in The Ksar Bouhamed fauna.

Diagnosis.— Pericyclus which is pachyconic at 8 mm diameter (ww/dm 0.65) and thickly discoidal at 15 mm (ww/dm 0.55). Umbilicus moderately wide (uw/dm 0.30 to 0.40). Umbilical margin rounded. Up to 35 rursiradiate, often dichotomising ribs per volution, which are strongest on the flanks and wedge out on the venter. Suture line with symmetrical adventive lobe.

1 10 100 conch diameter Description.—Apart from the general tendency in many Carboniferous goniatites to have more globose juveniles, no significant ontogenetic trend in the conch geometry of this species can be observed ( Fig. 25 ). In all stages available for study, the whorl cross section is depressed with broadly rounded flanks and venter. The umbilical margin is also rounded, and the umbilical wall is rather steep.

Specimens smaller than 4 mm (inner whorls of paratype MB.C.3966) are smooth except for four or more steinkern constrictions. In larger specimens (e.g., the holotype MB.C.3962) a coarse ornament is expressed even on the steinkern, with approximately 30 to 35 sharp ribs which begin immediately at the umbilical margin. From there they run in backward direction and form a shallow lateral sinus and a barely visible ventrolateral salient. On the venter they turn back to form a deeply, rounded chevron−shaped sinus, but on the midventer they wedge out and thus are hardly visible on the midventer. Many of the ribs dichotomise on the umbilical margin. The constrictions of the steinkern become fewer during ontogeny. The holotype possesses only one, which parallels the ribs .

In the suture line of the holotype MB.C.3962 ( Fig. 26 ), all elements are low and wide. The external lobe is V−shaped with sinuous flanks, and the median saddle is low (less than 0.20 of the external lobe depth). Both the broadly rounded ventrolateral saddle and the V−shaped adventive lobe are symmetrical .

Dimensions.—(in mm). Comparisons.— Pericyclus isagenuswithspecieswhichwere described mainly in the 19 th century and thus revision is required for most of them. P. princeps (de Koninck, 1844) has a very similar conch, but a narrower umbilicus (uw/dm less than 0.30) and has ribs which cross the venter. P. ryckholti (de Koninck, 1880) and P. divisus (de Koninck 1880) have a very narrow umbilicus (uw/dm less than 0.20) and faint ribs. P. foordi Crick, 1899 and P. trapezoidalis Crick, 1899 are based on large specimens (more than 100 mm in diameter) and thus difficult to compare. Finally, P. latumbilicatus Kusina, 2000 resemblesthenewspeciesinitsornament,buthasawiderumbilicus (uw/dm more than 0.45) than P. mercatorius sp. nov.

Figures

Fig. 25. Whorl width/ conch diameter and umbilical width/ conch diameter ratios of Pericyclus mercatorius sp. nov.

Fig. 26. Suture line of Pericyclus mercatorius sp. nov.; holotype MB.C.3962 at dm 11.4 mm, ww 7.1 mm, wh 4.7 mm; × 10.