Domatoceras ocomphalum, Korn & Hairapetian, 2025

Domatoceras ocomphalum sp. nov.

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Fig. 7 View Fig ; Table 3 View Table 3

Diagnosis

Species of Domatoceras with extremely discoidal, subevolute conch (ww/dm ~ 0.28; uw/dm ~ 0.38), weakly compressed whorl profile (ww/wh ~0.70) and extremely high coiling rate (WER ~2.60) at a conch diameter of 60 mm. Whorl profile with flat venter, angular ventrolateral shoulder, convergent flanks, subangular umbilical margin and steep and flattened umbilical wall. Whorl overlap very small. Without sculpture. Suture line with a small and narrow external lobe and a much larger and deeper, broadly rounded lateral lobe.

Etymology

From the Greek ‘ομφαλός’= ‘umbilicus’ and ‘ὀξύς’=‘sharp’; because of the subangular umbilical margin.

Type material

Holotype

IRAN – Esfahan Province • Baghuk Mountain ; Hambast Formation, Vedioceras beds ( late Wuchiapingian); 2010; Korn et al. leg.; illustrated in Fig. 7 View Fig ; MB.C.32109 .

Description

Holotype MB.C.32109 is a partially corroded specimen with a conch diameter of about 80 mm. It allows the study of two whorls ( Fig. 7B View Fig ). The conch is, at 62 mm diameter, extremely discoidal and subevolute (ww/dm = 0.28; uw/dm =0.38) with an extremely high coiling rate (WER =2.58); the whorl profile is compressed (ww/wh = 0.70) with a completely flat venter, an angular ventrolateral shoulder, weakly convex and convergent flanks, a subangular umbilical margin and a flattened and steep umbilical wall ( Fig. 7A View Fig ). The specimen is free of sculpture. The suture line shows a shallow, rounded external lobe and a three times larger, broadly rounded lateral lobe. A small, incipient lobe is visible on the umbilical wall ( Fig. 7C View Fig ).

Remarks

Domatoceras ocomphalum sp. nov. differs from D. canonium sp. nov. in the shape of the umbilicus. Its wall is flattened and steep in D. ocomphalum but convex and oblique in D. canonium . The umbilical margin is subangular in D. ocomphalum but rounded in D. canonium . Furthermore, D. ocomphalum lacks ventrolateral tubercles in the juvenile stage.

Domatoceras ocomphalum sp. nov. differs from D. myloide sp. nov. in the more strongly convergent flanks, which in the latter species are almost parallel and in the flat venter bounded by an angular ventrolateral shoulder, while the venter is convex and bounded by a rounded ventrolateral shoulder in D. myloide .

Domatoceras ocomphalum sp. nov. has conch proportions similar to D. elegantulum and D. multituberculatum from Julfa, but differs from these species in the lack of ventrolateral nodes in the intermediate stage and the more angular umbilical margin and ventrolateral shoulder.