Tainoceras latecostatum, Korn & Ghaderi, 2025

Tainoceras latecostatum sp. nov.

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Fig. 35 View Fig ; Table 21 View Table 21

Diagnosis

Species of Tainoceras with discoidal, subevolute conch (ww/dm ~ 0.45; uw/dm ~ 0.33) and weakly depressed whorl profile (ww/wh ~1.15) at a conch diameter of about 100 mm. Whorl profile hexagonal with gently convergent flanks; venter tectiform with broad longitudinal midventral groove, flanks flattened, umbilical margin narrowly rounded. Sculpture with about 20 sharp, coarse ribs on the flank per volution; venter with one row of hump-like, low nodes adjacent to the longitudinal groove. Suture line with a rather deep, tongue-shaped external lobe and a broadly rounded lateral lobe.

Etymology

Combination of the Latin ‘ late ’ (adv.) = ‘broadly’ and ‘ costatum ’ (adj., n.) = ‘ribbed’; because of the coarse ribs on the flanks.

Type material

Holotype

IRAN – East Azerbaijan • Ali Bashi 4 ; Vedioceras Beds of the Julfa Formation ( late Wuchiapingian); 2018; Ghaderi leg.; illustrated in Fig. 35 View Fig ; MB.C.32061 .

Description

Holotype MB.C.32061 is a fragment of a phragmocone with an estimated conch diameter of 95 mm ( Fig. 35B View Fig ). It is slightly tectonically distorted, but nevertheless allows the conch geometry to be recognised quite well; it can be estimated that the width of the umbilicus is about one third of the conch diameter. The whorl profile is weakly depressed with a whorl width of 45 mm and a whorl height of 39 mm; the venter is convex and has a median longitudinal groove with a width of about 12 mm. The weakly convergent flanks are flattened and bordered by a rounded ventrolateral shoulder and a rounded umbilical margin ( Fig. 35A View Fig ).

The sculpture consists of a combination of ribs and nodes. On the flank, five very strong ribs are present on a quarter of a volution; these begin at a short distance from the umbilical margin and extend in slight forward direction with a shallow lateral sinus across the flank. In the ventrolateral region they increase in strength and form sharp ridges ending in ventrolateral nodes. These continue a short distance towards the lateral side of the venter, where they are directed backwards. Very low and bluntly rounded hump-like conical nodes occur immediately adjacent to the median longitudinal groove; these nodes correspond to the ribs on the flanks. The suture line shows a tongue-shaped external lobe and a broadly rounded lateral lobe ( Fig. 35C View Fig ).

Remarks

A new species is established here, although only one fragmentary specimen is available. The reason for this is the peculiar sculpture of Tainoceras latecostatum sp. nov., which consists of a combination of ribs on the flanks and one row of very low, hump-like nodes on the venter. It is especially the coarse ribs that give the new species a unique position in the genus; other species possess conical nodes on the flanks instead.

In lateral view, with the narrowly rounded umbilical margin, the flattened flanks and the somewhat concave ribs, the new species bears some resemblance to the species of the genus Serometacoceras gen. nov., but differs in the ventral longitudinal groove and the ventral nodes.