Tardunautilus nimius, Korn & Ghaderi, 2025

Tardunautilus nimius gen. et sp. nov.

urn:lsid:zoobank.org:act:

Figs 30–31 View Fig View Fig ; Table 17 View Table 17

Diagnosis

Species of Tardunautilus gen. nov. with thickly discoidal, evolute conch (ww/dm ~0.53; uw/dm ~0.47), moderately depressed whorl profile (ww/wh ~ 1.80) and moderately high coiling rate (WER ~ 1.95) at a conch diameter of 150 mm. Whorl profile rounded trapezoidal with strongly divergent flanks; venter broadly rounded, area of flanks and umbilical wall weakly concave. Sculpture with two rows of ventrolateral nodes in the intermediate growth stage. Suture line with very broad and shallow external lobe, slightly deeper, broadly rounded lateral lobe and broadly rounded internal lobe.

Etymology

From the Latin ‘ nimius ’ (adjective, m.) =‘very large’; because of the large size of the conch.

Type material

Holotype

IRAN – East Azerbaijan • Zal ; Zal Member of the Ali Bashi Formation ( early Changhsingian); 2018; Ghaderi leg.; illustrated in Fig. 30–31 View Fig View Fig ; MB.C.32057 .

Description

The single holotype MB.C.32057 is a fragment consisting of about a quarter of two volutions; the reconstructed diameter of the specimen is approximately 148 mm ( Fig. 30 View Fig ). The reconstructed conch is thickly discoidal and evolute (ww/dm ~0.53; uw/dm ~0.47). The whorl profile is moderately depressed (ww/wh ~ 1.80) and rounded trapezoidal with a broadly convex venter, a pronounced ventrolateral shoulder and a slightly concave zone consisting of flanks and umbilical wall; the whorl overlap is very small ( Fig. 31A–B View Fig ). It appears that the last preserved whorl slowly detaches from the preceding whorl. The profile of the penultimate whorl shows a more flattened venter, a more pronounced ventrolateral shoulder and flattened flanks.

The sculpture is well-preserved on the penultimate whorl. It consists of paired conical nodes on the flank; one row of nodes is located in the midflank area and the other row has a position on the ventrolateral shoulder. The nodes of each pair are connected by a low rib. Six of these node pairs occur on a quarter volution. On the last whorl, no nodes are visible.

The suture line extends with a very shallow external lobe, a broadly rounded and shallow lateral lobe and a rounded internal lobe ( Fig. 31C View Fig ). The chambers are rather short; the septa are arranged in distances of about 14 degrees. The siphuncle has a dorsocentral position near the centre of the septum.

Remarks

Tardunautilus nimius gen. et sp. nov. differs from T. minor gen. et sp. nov. in the presence of two rows of conical nodes on the flank, while T. minor has only one such row on the ventrolateral shoulder. Furthermore, the whorl profile is much more depressed in T. nimius (ww/wh ~1.80) than in T. minor (ww/wh ~ 1.50).