Domatoceras multituberculatum, Korn & Ghaderi, 2025

Domatoceras multituberculatum sp. nov.

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Fig. 9 View Fig ; Table 2 View Table 2

Diagnosis

Species of Domatoceras with extremely discoidal, subevolute conch (ww/dm ~0.28; uw/dm ~ 0.38), weakly compressed, inverted trapezoidal whorl profile (ww/wh ~0.75) and very high coiling rate (WER ~ 2.35) at a conch diameter of 75–100 mm. Whorl profile with flat venter, subangular ventrolateral shoulder, gently convergent, flattened flanks and narrowly rounded umbilical margin. Ornament with fine growth lines and with small ventrolateral conical tubercles in the preadult stage. Suture line with a narrow and shallow external lobe and a much larger and deeper, broadly rounded lateral lobe.

Etymology

Combination of the Latin ‘ multus ’ (adj., m.) =‘many’ and ‘ tuberculum ’ (noun, n.) =‘tubercle’; because of the ventrolateral sculpture.

Type material

Holotype

IRAN – West Azerbaijan • Aras Valley; Araxoceras Beds of the Julfa Formation (early Wuchiapingian); 2011; Korn et al. leg.; illustrated in Fig. 9A–D View Fig ; MB.C.31997 .

Paratypes

IRAN – West Azerbaijan • 1 specimen; same data as for holotype; illustrated in Fig. 9G–I View Fig ; MB.C.31998 • 1 specimen; Aras Valley; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 9G–I View Fig ; MB.C.31999 • 1 specimen; Aras Valley; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 9J–K View Fig ; MB.C.32000 • 1 specimen; Aras Valley ; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; MB.C.32001 . – East Azerbaijan • 1 specimen; Ali Bashi 4; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 9L–M View Fig ; MB.C.32002 .

Description

Holotype MB.C.31997 is a quarter volution of a phragmocone with a maximum whorl height of 36 mm, meaning that the phragmocone diameter was about 100 mm. It allows the study of three whorls, in which the ontogenetic change of conch geometry and sculpture can be observed ( Fig. 9A View Fig ). While the ww/wh ratio is 0.87 in the penultimate volution, it is reduced to 0.75 in the last volution. Furthermore, the venter shows increased flattening during this growth interval. However, even the last 90 degrees of the phragmocone show some variation; the shape of the venter varies from slightly concave to slightly convex ( Fig. 9B–C View Fig ). The flanks are nearly flat, the umbilical margin is narrowly rounded and the flattened umbilical wall is oblique.

There is no sculpture visible on the last whorl, but the two whorls before show shallow and broad ventrolateral tubercles, which in the third-last whorl even shows a prolongation into ribs that are connected with barely visible umbilical nodes. The specimen has rather narrowly standing septa; on the last quarter volution of the phragmocone there are nine septa with a trend to crowding at the end ( SD ~10 degrees in average). The terminal suture line has a very shallow external lobe, a broadly rounded lateral lobe and a very shallow, ventrally inclined lobe on the umbilical wall ( Fig. 9D View Fig ).

Paratype MB.C.31998 is, though incomplete, one of the best in the available material ( Fig. 9G View Fig ). It is a fully septate specimen with an estimated diameter of about 73 mm and allows the study of two whorls of the phragmocone. The estimated ww/dm and uw/dm ratios are 0.31 and 0.37, respectively. The whorl profile is weakly compressed (ww/wh =0.79) with a nearly flat venter, a pronounced subangular ventrolateral shoulder and flattened, weakly convergent flanks. The whorls are widest at the narrowly rounded umbilical margin ( Fig. 9H View Fig ).

The last whorl of the phragmocone appears to be free of sculpture, but the penultimate whorl shows rather coarse, low ventrolateral conical nodes, which are arranged in distances of about 15 degrees. The suture line has a very shallow external lobe, a subangular ventrolateral saddle (with a position at the ventrolateral shoulder) and a broadly rounded, shallow lateral lobe. Additionally, a very shallow, small and rounded lobe is visible on the umbilical wall ( Fig. 9I View Fig ). Both the last and the penultimate whorl show six chambers on a quarter of a volution ( SD ~ 15 degrees).

A complete suture line is visible in the fragmentary paratype MB.C.32000. It shows a rather narrow and shallow external lobe, a broadly rounded lateral lobe that has three times the depth of the external lobe. The specimen shows a rather narrow internal lobe of three quarters the depth of the lateral lobe ( Fig. 9K View Fig ). The smaller fragmentary paratypes MB.C.31999 ( Fig. 9E–F View Fig ) and MB.C.32002 ( Fig. 9L–M View Fig ) show the variation of the depth of the external lobe.

Remarks

Domatoceras multituberculatum sp. nov. differs from D. elegantulum sp. nov. in the conical ventrolateral nodes of the preadult whorls, the slightly more evolute and stouter conch, the less compressed whorl profile and the narrowly rounded umbilical margin.

Domatoceras multituberculatum sp. nov. differs from D. convergens by the less strongly convergent flanks and the much wider whorl profile (ww/wh ~ 0.80 in contrast to D. convergens with ~ 0.60) at a conch diameter of 75 mm. The venter is much wider in D. elegantulum sp. nov. when compared to D. convergens .