Shahrezanautilus ghaderii, Korn & Hairapetian, 2025

Shahrezanautilus ghaderii gen. et sp. nov.

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Fig. 31 View Fig ; Table 24 View Table 24

Diagnosis

Species of Shahrezanautilus gen. nov. with thinly pachyconic, involute conch (ww/dm ~ 0.62; uw/dm ~0.13), weakly depressed whorl profile (ww/wh ~1.10) and extraordinarily high coiling rate (WER ~ 3.10) at a conch diameter of 80 mm. Whorl profile with convex venter, convex and convergent flanks, a subangular umbilical margin, a steep umbilical wall and a moderately deep imprint zone ( IZR ~0.25). Suture line with a very shallow external lobe and a weakly asymmetric, broadly rounded lateral lobe.

Etymology

Named after Abbas Ghaderi (Mashhad), in honour of his contribution in studying the Permian–Triassic boundary.

Type material

Holotype

IRAN – Esfahan Province • Baghuk Mountain ; Hambast Formation, Vedioceras beds ( late Wuchiapingian); 2011; Korn et al. leg.; illustrated in Fig. 31 View Fig ; MB.C.32150 .

Description

Holotype MB.C.32150 is a largely chambered specimen with a conch diameter of 84 mm ( Fig. 31B View Fig ), which is heavily corroded on the last half volution. Some of the conch parameters on the last half volution can only be reconstructed. The conch is thinly pachyconic and involute (ww/dm ~ 0.62; uw/dm=0.13) with an extraordinarily high coiling rate (WER =3.09) and a moderately deep whorl overlap ( IZR = 0.25). The whorl profile is weakly depressed (ww/wh ~ 1.08) with a convex venter, convex convergent flanks, a narrowly rounded umbilical margin and a steep umbilical wall ( Fig. 31A View Fig ). The suture line shows a very shallow, rounded lobe on venter and a broadly rounded, nearly symmetric lateral lobe ( Fig. 31C View Fig ).

Remarks

Shahrezanautilus ghaderii gen. et sp. nov. differs from S. weyeri gen. et sp. nov. in having a much narrower umbilicus; the uw/dm ratio is about 0.15 in S. ghaderii but about 0.25 in S. weyeri . This difference parallels a difference in the whorl overlap rate, which is about 0.25 in S. ghaderii , but only 0.07 in S. weyeri and in the coiling rate, which is lower in S. ghaderii (WER ~ 3.00 compared to about 3.40 in S. weyeri ).

Shahrezanautilus ghaderii gen. et sp. nov. has some similarities with Julfanautilus ashourii Korn & Ghaderi, 2025 from Julfa. Like S. ghaderii , J. apertum has a stout, involute conch (ww/dm ~ 0.65), which is more umbilicated in J. apertum (uw/dm ~ 0.25 in J. apertum, but only 0.15 in S. ghaderii ). The main difference between the two species is the shape of the venter, which is convex in S. ghaderii and concave in J. apertum.