Corotainoceras inerme, Korn & Ghaderi, 2025

Korn, Dieter & Ghaderi, Abbas, 2025, Late Permian nautiloids from Julfa (NW Iran), European Journal of Taxonomy 1018, pp. 1-113 : 74

Corotainoceras inerme gen. et sp. nov.

urn:lsid:zoobank.org:act:

Fig. 37 ; Table 22

Diagnosis

Species of Corotainoceras with thinly pachyconic, subevolute conch (ww/dm ~ 0.62; uw/dm ~ 0.30), weakly depressed whorl profile (ww/wh ~1.45) and extremely high coiling rate (WER ~ 2.55) at a conch diameter of 100 mm. Whorl profile inverted trapezoidal with gently convergent flanks; venter tectiform with broad longitudinal midventral groove, flanks flattened, umbilical margin broadly rounded. Sculpture with about 6 coarse blunt conical nodes on the umbilical margin per volution; venter without nodes. Suture line with shallow external lobe, very shallow ventrolateral lobe and broadly rounded lateral lobe.

Etymology

From the Latin ‘ inerme ’ (adjective, n.)=‘unarmed’; because of the lack of nodes on the venter.

Type material

Holotype

IRAN – East Azerbaijan • Zal; Araxoceras Beds of the Julfa Formation ( early Wuchiapingian); 2013; Korn et al. leg.; illustrated in Fig. 37 ; MB.C.32063.

Description

Specimen MB.C.32063 is a partly corroded, but otherwise fairly well-preserved, fully chambered specimen with a conch diameter of 101 mm; the total diameter including the body chamber has been about 150 mm. It allows the study of one volution ( Fig. 37A ). It is thinly pachyconic and subevolute (ww/dm= 0.62; uw/dm=0.30) with a weakly depressed whorl profile (ww/wh =1.44) and an extremely high coiling rate (WER= 2.53). The whorl profile is widest at the broadly rounded umbilical margin, from where the steep umbilical wall approaches the umbilical seam. The flanks converge strongly towards the broadly rounded but distinct ventrolateral shoulder. The shape of the venter in the whorl profile is tectiform with a 16 mm wide midventral groove ( Fig. 37B ). The sculpture consists of six prominent, isolated conical umbilical nodes in the last volution; these become weaker in the course of the last volution. No nodes are visible on the venter. The suture line has a prominent but rounded external lobe and a wide and shallow lateral lobe showing a weak subdivision by a low saddle (with the position at the ventrolateral shoulder; Fig. 37C ).

Remarks

Corotainoceras inerme gen. et sp. nov. has a conch shape similar to that of some species of Tainoceras and the new genus D to be described by Korn & Hairapetian (in press); this means that the whorl profile is inverted trapezoidal with rapidly converging flanks, a wide venter and a very steep umbilical wall. However, species such as T. duttoni , E. dorsoplicaum and E. lutense have rows of tubercles on the ventral side. The latter lacks the umbilical nodes, which are developed as longitudinal tubercles in T. duttoni .

Figures

Fig. 37. Corotainoceras inerme gen. et sp. nov., holotype MB.C.32063 (Korn et al. 2013 Coll.) from the Araxoceras Beds of the Julfa Formation at Zal. A. Lateral and apertural views. B. Reconstruction of apertural view. C. Suture line at ww =56.0 mm, wh =36.0 mm. Scale bar units =1 mm.