Aifinautilus icanus, Korn & Hairapetian, 2025

Aifinautilus icanus gen. et sp. nov.

urn:lsid:zoobank.org:act:

Figs 11–13 View Fig View Fig View Fig ; Table 7 View Table 7

Diagnosis

Species of Aifinautilus gen. nov. with thickly discoidal, subinvolute conch (ww/dm ~ 0.50; uw/dm ~ 0.25), weakly depressed whorl profile (ww/wh ~ 1.10) and very high coiling rate (WER ~ 2.30) at a conch diameter of 110 mm. Whorl profile with weakly concave venter, rounded ventrolateral shoulder, weakly convergent flanks, rounded umbilical wall, weakly concave umbilical wall and moderately deep imprint zone ( IZR ~ 0.25). Without sculpture. Suture line with a very shallow external lobe and a very shallow lateral lobe.

Etymology

From the Greek ‘ἱκανός‘ =‘competent’; because of the robust conch.

Type material

Holotype

IRAN – Esfahan Province • Baghuk Mountain ; Hambast Formation, Araxoceras beds ( early Wuchiapingian); 2010; Korn et al. leg.; illustrated in Figs 11–12 View Fig View Fig ; MB.C.32116 .

Paratypes

IRAN – Esfahan Province • 1 specimen; same data as for holotype; 2011; Korn et al. leg.; illustrated in Fig. 13 View Fig ; MB.C.32117 • 3 specimens; same data as for holotype; 2011; Korn et al. leg.; MB.C.32118 to MB.C.32120.

Description

Holotype MB.C.32116 is an almost complete, but partially corroded specimen with a conch diameter of 114 mm ( Figs 11 View Fig , 12A View Fig ). It is largely chambered; only a small part of the specimen belongs to the body chamber. The conch is, at a conch diameter of 114 mm, thickly discoidal and subinvolute (ww/ dm = 0.48; uw/dm = 0.24) with a very high coiling rate (WER= 2.31) and moderately wide whorl overlap ( IZR =0.23). The whorl profile is weakly depressed (ww/wh = 1.09) with a slightly concave venter that is bordered by a rounded ventrolateral shoulder; the flanks are broadly convex and weakly convergent. The umbilical margin is narrowly rounded and the umbilical wall is steep and weakly incurved. The last whorl shows a modification in the profile. At the beginning it is inverted trapezoidal with fairly convergent flanks and a subangular ventrolateral shoulder ( Fig. 12B View Fig ). The specimen does not show any traces of sculpture. The length of the phragmocone chambers shows considerable changes during the last volution. The first quarter of this whorl consists of six chambers (CLI = 15); considerable septal crowding at the end of the phragmocone causes the number to increase to about 12 (CLI =7.5). Especially the last six septa are very closely spaced. The suture line shows a shallow and broadly rounded external lobe, a narrowly rounded ventrolateral saddle, a shallow lateral lobe twice as deep than the external lobe and a very small umbilical lobe ( Fig. 12C View Fig ).

Paratype MB.C.32117 is an incomplete, fully chambered specimen with a conch diameter of 63 mm ( Fig. 13B View Fig ). It corresponds largely to the holotype in its conch proportions and also shows a weakly concave umbilical wall, almost parallel flanks, a rounded but pronounced ventrolateral shoulder and a weakly concave venter ( Fig. 13A View Fig ). The suture line has a shallow external lobe, a narrowly rounded ventrolateral saddle and a broadly rounded lateral lobe that is twice as deep as the external lobe ( Fig. 13C View Fig ).

Remarks

Specimens of Aifinautilus icanus gen. et sp. nov. can hardly be confused with any other species of Baghuk Mountain. Species of the genus Ocunautilus gen. nov. show similarities in conch shape, but there are some easily recognisable differences. In A. icanus , the flanks are almost parallel, while in the species of Ocunautilus they are distinctly convergent. Another distinguishing criterion is the coiling rate, which is considerably lower in A. icanus (WER ~ 2.25) than in Ocunautilus (WER mostly over 3.00).

There are great similarities of A. icanus gen. et sp. nov. to species of the Triassic genus Germanonautilus . For example, A. icanus shows very close agreement in conch morphology with G. bidorsatus (Schlotheim, 1820) , as was shown by Dzik (1984: 166, text-fig. 64). However, Germanonautilus differs from Aifinautilus gen. nov. by the presence of an annular lobe.