Serometacoceras dorashamense (Shimansky, 1965), 2025

Korn, Dieter & Ghaderi, Abbas, 2025, Late Permian nautiloids from Julfa (NW Iran), European Journal of Taxonomy 1018, pp. 1-113 : 38-41

Serometacoceras dorashamense (Shimansky, 1965) gen. et comb. nov.

Fig. 18 ; Table 10

Metacoceras dorashamense Shimansky, 1965b: 157 , pl. 14 fig. 3.

Pleuronautilus sp. indet. 1 – Teichert & Kummel 1973: 418, pl. 1 figs 3–4.

Pleuronautilus sp. – Gliwa et al. 2020: text-fig. 17b.

non Metacoceras dorashamense – Teichert & Kummel 1973: 416, pl. 4 figs 5–6.

Diagnosis

Species of Serometacoceras gen. nov. with thickly discoidal, subevolute conch (ww/dm =0.45–0.50; uw/dm= 0.35–0.40), weakly depressed whorl profile (ww/wh = 1.20–1.30) and very high coiling rate (WER =2.30–2.50) at a conch diameter of 50 mm. Whorl profile nearly rectangular, usually with gently divergent flanks; venter and flanks flattened. Sculpture with 10–12 low ventrolateral nodes per volution; the nodes are connected by slightly curved ribs with weak nodes on the umbilical margin. Suture line with a broad and shallow external lobe and a usually slightly deeper, broadly rounded lateral lobe.

Type material

Holotype

AZERBAIJAN • Dorasham ; Araxoceras Beds (early Wuchiapingian); illustrated by Shimansky (1965b: pl. 14 fig. 3); PIN 1572 /246.

Material examined

IRAN – West Azerbaijan • 1 specimen; Aras Valley; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2013; Korn et al. leg.; illustrated in Fig. 18A–C ; MB.C.29347 • 1 specimen; same data as for preceding; 2018; Korn et al. leg.; illustrated in Fig. 18D–F ; MB.C.32029 • 1 specimen; same data as for preceding; 2018; Ghaderi leg.; illustrated in Fig. 18G–I ; MB.C.32030 • 1 specimen; same data as for preceding; 2018; Ghaderi leg.; illustrated in Fig. 18J–L ; MB.C.32031 • 5 specimens; same data as for preceding; 2018; Ghaderi leg.; MB.C.32032 to MB.C.32036 • 1 specimen; same data as for preceding; 2011; Korn et al. leg.; MB.C.32037 • 2 specimens; same data as for preceding; Korn et al. 2013, 2018 Coll.; MB.C.32038 , MB.C.32039 . – East Azerbaijan • 2 specimens; Ali Bashi 4; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; MB.C.32040 , MB.C.32041 • 1 specimen; Ali Bashi main valley; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; MB.C.32042 • 1 specimen; Zal; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; MB.C.32043 .

Description

Specimen MB.C.29347 is a 120-degree long segment consisting of part of the body chamber and two chambers of the phragmocone. The total diameter can be estimated at approximately 60 mm ( Fig. 18B ). The specimen has a subquadrate whorl profile with a flattened venter, a rounded ventrolateral shoulder, slightly divergent and weakly concave flanks and a rounded umbilical margin ( Fig. 18A ).

The sculpture consists of coarse ribs that deviate slightly from the radial direction towards the aperture. They emerge on the inner flank near the umbilical margin with a slightly tubercular thickening, become more prominent in the middle of the flank and, after tapering further, end close to the ventrolateral shoulder in a blunt and elongated tubercle. Ribs and nodes are asymmetrically arranged and not arranged in exact correspondence on both sides of the conch.

Specimen MB.C.32029 is a phragmocone segment of 120 degrees length ( Fig. 18E ). Its maximum whorl height is 20 mm, which corresponds to a conch diameter of about 50 mm. The whorl profile is weakly depressed and subquadrate (ww/wh= 1.30) and almost widest at the rounded umbilical margin, from where the flanks very slowly diverge towards the rounded ventrolateral shoulder ( Fig. 18D ). The venter is flattened and possesses a very shallow concave depression at the beginning of the whorl segment. The sculpture shows five prominent ribs on the segment. These ribs originate at the umbilical margin and extend radially across the flanks; in the outer flank area they strengthen significantly to form large and rounded nodes. The suture line has a rather small and shallow external lobe and a large rounded lateral lobe with asymmetric shape (the ventral side is much longer than the dorsal) and a very shallow, small lobe on the umbilical wall ( Fig. 18F ).

The fragmentary specimen MB.C.32030 ( Fig. 18G ; 21 mm whorl height) has a similar shape as specimen MB.C.32029, but is less depressed (ww/wh = 1.19). The ribs are not as coarse as in the other specimens and the suture line possesses a deeper external lobe ( Fig. 18I ). The septa are densely arranged at intervals averaging about 10 degrees only.

Specimen MB.C.32031 ( Fig. 18J ) is a fragment with 22 mm whorl height and possesses a subquadrate whorl profile (ww/wh=1.19) with weakly divergent flanks ( Fig. 18K ). Its sculpture consists of coarse and sharp ribs and the suture line shows a comparatively narrow and deep external lobe ( Fig. 18L ). The septa are spaced at intervals averaging about 15 degrees.

Remarks

Serometacoceras dorashamense gen. et comb. nov. was established by Shimansky (1965b) mainly on the basis of a rather small holotype with a conch diameter of only 35 mm. The type specimen still shows some early ontogenetic features, such as the distinctly angular umbilical margin and the rather coarse ribs. Although the new material from Iran only consists of fragments, their juvenile morphology can also be seen in the inner whorls of several of the larger specimens. Therefore, an assignment of this material to S. dorashamense is fairly certain. The larger specimens from Iran show weakening of the ribs and nodes.

Serometacoceras dorashamense gen. et comb. nov. differs from S. dorsoarmatum gen. et comb. nov. in possessing rather coarse ribs on the flanks and small tubercles around the umbilicus. The umbilicus is somewhat narrower in S. dorashamense (uw/dm = 0.35–0.40 when compared to 0.40–0.45 in S. dorsoarmatum ).

Another species with similar morphology is S. verae gen. et comb. nov. but this differs from S. dorashamense gen. et comb. nov. in the more clearly developed umbilical nodes and the occasional presence of an additional row of nodes in the midflank region. A further distinguishing feature is the shape of the venter; in S. dorashamense it is flattened and in S. verae broadly rounded.

Figures

Fig. 18. Serometacoceras dorashamense (Shimansky, 1965) gen. et comb. nov. from the Araxoceras Beds of the Julfa Formation. A. Specimen MB.C.29347 (Korn et al. 2013 Coll.) from Aras Valley, reconstruction of apertural view.B. The same specimen, lateral and ventral views. C. The same specimen, suture line at ww =19.8 mm, wh= 20.4 mm. D. Specimen MB.C.32029 (Korn et al. 2018 Coll.) from Aras Valley, whorl profile. E. The same specimen; lateral and ventral views. F. The same specimen, suture line at ww =20.8 mm, wh =15.8 mm. G. Specimen MB.C.32030 (Ghaderi 2018 Coll.) from Aras Valley, ventral and lateral views. H. The same specimen, whorl profile. I. The same specimen, suture line at ww =21.5 mm, wh=19.5 mm. J. Specimen MB.C.32031 (Ghaderi 2018 Coll.) from Aras Valley, lateral view. K. The same specimen, whorl profile. L. The same specimen; suture line at ww =24.2 mm, wh= 18.9 mm. Scale bar units =1 mm.

Fig. 21. Serometacoceras cingulum gen. et sp. nov., holotype MB.C.32050 (Korn et al. 2013 Coll.) from the Araxoceras Beds of the Julfa Formation of Zal. A. Lateral and ventral views. B. Whorl profile. C. Suture line at ww =28.4 mm, wh=19.3 mm. Scale bar units =1 mm.

Tables

Table 10. Conch dimensions (in mm) and ratios of Serometacoceras dorashamense Shimansky, 1965 gen. et comb. nov.; reconstructed dimensions and ratios in italics.

Nr.	dm	ww	wh	uw	ah	ww/dm	ww/wh	uw/dm	WER	IZR
MB.C.29347	60.0	24.2	21.5	19.0	20.5	0.40	1.13	0.32	2.31	0.05
MB.C.32031	57.1	26.4	22.2	21.1	20.5	0.46	1.19	0.37	2.44	0.08
MB.C.32030	54.3	27.4	21.2	19.8	19.2	0.50	1.29	0.36	2.39	0.09
MB.C.32029	48.7	23.6	18.2	18.0	17.0	0.48	1.30	0.37	2.36	0.07