Girtyoceratidae Wedekind, 1918

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 : 87-88

publication ID	https://doi.org/ 10.5281/zenodo.13272527
persistent identifier	https://treatment.plazi.org/id/03BE87DE-5A60-FFD5-FCF8-FF7974D5FC53
treatment provided by	Felipe
scientific name	Girtyoceratidae Wedekind, 1918
status

Treatment

Family Girtyoceratidae Wedekind, 1918 View in CoL Winchelloceras Ruzhencev, 1965

Type species: Goniatites allei Winchell, 1862 .

Winchelloceras antiatlanteum sp. nov.

Figs. 28 View Fig , 29 View Fig , 30A–C View Fig .

Derivation of name: After the Anti−Atlas of Morocco.

Holotype: Specimen MB.C.3968 (coll. Klug), Fig. 30B View Fig .

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

Material.— 52 specimens, many of them are complete phragmocones, 5 to 17 mm in diameter.

Diagnosis.— Winchelloceras with thickly discoidal conch at 8 mm diameter (ww/dm 0.55) and at 15 mm diameter (ww/dm 0.45). Umbilicus narrow between 8 and 15 mm diameter (uw/dm0.20to0.28),umbilicalmarginsubangular.Steinkerns with four to six constrictions. Suture line with wide, V−shaped external lobe, low median saddle, broadly rounded ventrolateral saddle, and asymmetrical adventive lobe.

Description.—Specimens of all growth stages show a similar conch geometry with angular umbilical margin and convex flanks and venter ( Fig. 28 View Fig ). As can be seen in the table of dimensions, there are two ontogenetic trends observable. Firstly the whorl width/ conch diameter ratio decreases from 0.60 to 0.45between6and16mmdiameter,andsecondlytheaperture becomes higher in larger growth stages, with the whorl expansion rate rising from 1.70 to 2.00. The umbilical width is a rather plastic character, with a uw/dm varying between 0.15 and 0.28, and there appears to be no dependence on the ontogenetic stage.

There are four to six constrictions per volution. They begin at the subangular umbilical edge and follow a biconvex course across the flank with low dorsolateral projection, very shallow lateral sinus, low ventrolateral projection, and deep ventral sinus across the venter. In the interspaces between the constrictions, a faint undulation, following the course of the constrictions can be seen.

In the holotype MB.C.3969 ( Fig. 29 View Fig ), the suture line shows a wide and V−shaped external lobe with a low median saddle. The flanks of the external lobe are slightly sinuous, and the two prongs are very narrow. The wide and broadly rounded ventrolateral saddle is almost symmetrical, and the adventive lobe is symmetrical and V−shaped with gently curved flanks .

Dimensions.—(in mm). Comparisons.—It is difficult to compare the species of Winchelloceras of different sizes. Also it is not clear, which of the many specimens illustrated by Miller and Garner (1955) do in fact belong to W. allei ( Winchell 1862) . At least the holotype of this species has an almost closed umbilicus and is thus dissimilar to W. antiatlanteum sp. nov. The holotype of W. ruzhencevi Kusina, 1971 is of large size (69 mm). At this stage, the venter is acute, the steinkern has no constrictions,andthesuturelinehasamuchnarrowerventrolateral saddle than W. antiatlanteum sp. nov. W. minutum Kusina, 1980 has a very narrow umbilicus (uw/dm 0.06) and also narrow sutural elements with an almost parallel−sided external lobe. W. dzhaprakense ( Popov, 1965) has a compressed conch (ww/dm less than 0.30), and that of W.(?) sonkulense ( Popov, 1965) is almost involute with closed umbilicus. W. palentinum Wagner−Gentis, 1982 is based on insufficient material, but the umbilicus is almost closed and the conchismorecompressedthanin W. antiatlanteum sp.nov. It is unclear if W. delepinei Kusina, 1971 belongs to this genus. The specimen was originally described by Delépine (1941) as “ Muensteroceras ”? ou “ Sagittoceras ”? sp. nov. from Erfoud is a lenticular and nearly involute conch.