Tardunautilus aperimos sp. nov.

urn:lsid:zoobank.org:act: E08EF718-C2F6-44E2-9D15-A879DA51D394

Fig. 19; Table 13

Diagnosis

Species of Tardunautilus with thinly discoidal, evolute conch (ww/dm ~ 0.35; uw/dm ~ 0.50), weakly depressed whorl profile (ww/wh ~1.50) and low coiling rate (WER ~ 1.70) at a conch diameter of 60 mm. Whorl profile rounded trapezoidal with flattened venter, rounded ventrolateral shoulder, strongly divergent flanks and very small imprint zone. Sculpture with 20 conical nodes on the outer flank per volution. Suture line with a very shallow external lobe and a very shallow lateral lobe.

Etymology

From the Greek ‘ἀπό’=‘from’ and ‘ἐρῆμος’=‘desert’; because of the origin of the material.

Type material

Holotype

IRAN – Esfahan Province • Baghuk Mountain; Hambast Formation, Prototoceras beds (early Wuchiapingian); 2012; Korn et al. leg.; illustrated in Fig. 19; MB.C.32125.

Description

Holotype MB.C.32125 is an internal mould with a conch diameter of 58 mm; it is nearly fully chambered (Fig. 19B). The conch is thinly discoidal and evolute (ww/dm =0.37; uw/dm =0.53) with a low coiling rate (WER= 1.70); the whorl profile is weakly depressed (ww/wh = 1.49) and rounded trapezoidal with a flattened venter, a rounded ventrolateral shoulder and strongly convex and divergent flanks (Fig. 19A). The specimen shows a whorl that only slightly embraces the preceding; the umbilical seam has a position on the venter of the preceding whorl. The sculpture consists of 20 blunt conical nodes in ventrolateral position. These nodes are slightly narrower than their interspaces. The suture line shows very shallow, broadly rounded lobes on the venter and the flank (Fig. 19C).

Remarks

Tardunautilus aperimos sp. nov. differs from the similar species T. minor of Julfa in the lower number of ventrolateral nodes (20 per whorl, but about 25 in T. minor) and the wider umbilicus (uw/dm ~ 0.53 in T. aperimos, but only ~ 0.47 in T. minor) at comparable conch diameters. Tardunautilus nimius from Julfa differs in the broader whorls and the double row of ventrolateral nodes.