Vestinautilus inflexus, Korn & Bockwinkel, 2022

Korn, Dieter & Bockwinkel, Jürgen, 2022, Early Carboniferous nautiloids from the Central Sahara, southern Algeria, European Journal of Taxonomy 831, pp. 67-108 : 89-91

Vestinautilus inflexus sp. nov.

urn:lsid:zoobank.org:act:

Figs 18–19 , Table 10

Diagnosis

Species of Vestinautilus with moderately depressed, rounded-triangular whorl profile (ww/wh ~ 1.95), venter weakly flattened, smooth, ventrolateral shoulder angular. Whorls not embracing. Ornament with three weak but sharp ridges on the flank. Septa inflexed to produce a deep external lobe.

Etymology

From the Latin ‘ inflexus ’, referring to the incurved septum.

Type material

Holotype ALGERIA • Mouydir , south of Oued Temertasset (locality MOU-D1); Argiles de Teguentour ( Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian); Korn et al. 2002 Coll.; illustrated in Fig. 18B ; MB.C.30472.1 .

Paratypes ALGERIA • 2 specimens; Mouydir , south of Oued Temertasset (locality MOU-D1); Argiles de Teguentour ( Upper Pericyclus-Progoniatites Assemblage; early late Tournaisian); Korn et al. 2002 Coll.; illustrated in Fig. 18A, C ; MB.C.30472.2 – MB.C.30472.3 .

Description

Holotype MB.C.30472.1 is a phragmocone fragment from a quarter whorl with 15 mm whorl height ( Fig. 18B ). It has a moderately depressed whorl profile (ww/wh = 1.94) with a flattened venter and broadly rounded lateral and dorsal zones. The ventrolateral shoulder is subangular and reinforced by two sharp longitudinal ridges; there are two more, weaker ridges on the outer flank ( Fig. 19B ). The suture line shows a broad external lobe, flattened at the base. This particular shape is caused by an inflexion of the septum on the middle of the venter. There is a narrowly rounded saddle on the ventrolateral shoulder and a shallow, broadly rounded lobe on the flank ( Fig. 19C ).

Paratype MB.C.30472.2 is a desert-polished specimen with half a whorl preserved; it has a diameter of 24.5 mm ( Fig. 18A ). It was sectioned and shows one and a half whorls, which possess a similar profile. The last preserved whorl does, at 24 mm conch diameter, not touch the preceding, but this may be caused by the lack of the original shell wall ( Fig. 19A ). The longitudinal ridges are only barely visible and rather weak when compared with the holotype. The suture line shows a deeper external lobe, which is less flattened at the base.

The smaller paratype MB.C.30472.3 ( Fig. 18C ) with 6 mm whorl height has a less depressed whorl profile, but shows very clearly the ventral inflexion of the septum and the resulting very deep external lobe ( Fig. 19E ).

Remarks

Vestinautilus inflexus sp. nov. belongs to the species of the genus with a moderately depressed whorl profile (ww/wh ~1.95) and thus ranges between the more slender species V. angulatus sp. nov. (ww/wh ~1.50) as well as V. papilio sp. nov. (ww/wh ~ 1.70) and the stouter species V. bicristatus sp. nov. (ww/ wh ~2.15). The new species differs from those species of the genus with a similar whorl profile in the very weak longitudinal ridges.

Figures

Fig. 18. Vestinautilus inflexus sp. nov. from Oued Temertasset (both Korn et al. 2002 Coll.). A. Paratype MB.C.30472.2. B. Holotype MB.C.30472.1. C. Paratype MB.C.30472.3. Scale bar units= 1 mm.

Fig. 19. Vestinautilus inflexus sp. nov. from Oued Temertasset (both Korn et al. 2002 Coll.). A. Cross section of paratype MB.C.30472.2. B. Whorl profile of holotype MB.C.30472.1. C. Suture line of holotype MB.C.30472.1, at ww =15.2 mm, wh=7.2 mm. D. Whorl profile of paratype MB.C.30472.3. E. Suture line of paratype MB.C.30472.3, ww =8.7 mm, wh=5.8 mm. Scale bar units =1 mm.