Hildaites calamantis, Sassaroli & Venturi, 2012

Sassaroli, Stefano & Venturi, Federico, 2012, Early Toarcian (post-OAE) Hildoceratinae (Ammonitina) fauna from the Marchean Apennines (Italy), Revue de Paléobiologie 31 (1), pp. 85-114 : 101-102

Hildaites calamantis n. sp.

Pl. IV, fig. 6; Pl. V, figs. 1a-c; Fig. 7, F-G; Fig. 8

Material: Six specimens of large and medium size, all coming from Marconessa quarry.

Derivatio nominis: From the surname of the owner of the SIELPA Company, which mine at Marconessa quarry and well known for his rudeness and discourtesy towards all fossil collectors and deep indifference for the advancement of science.

Holotype: A well preserved specimen of large size with the body chamber MSA85 from Marconessa quarry section 3, bed 4b (Pl. V, figs. 1a-b-c; Fig.7, F-G).

Stratus typicus: Nodular limestone and grey marls of the early Toarcian (Bugarone Formation).

Diagnosis: Evolute compressed shell with moderately overlap of the whorls, flattened sides, from subrectangular to swollen almost sub-quadrate whorl section mainly in the body chamber. The wide venter varies from tabulate in the inner whorls to rounded in the outer whorls with a strong and low keel. The umbilical wall is high and almost vertical and the umbilical edge is rounded. Sparse, fine not raised and bifurcating ribs, which have a sinuous retroverted appearance, showing a short not angled proximal segment and a moderate projection on the ventro-lateral edge. The ammonitic suture is more or less frilled, with well developed L and U 2 lobes.

Holotype measurements. D: 149 mm - U: 78 mm - U/D: 0.52 - Wb: 30 mm - Wh: 37 mm - Wh/Wb: 1.23 - Wb/ Wh: 0.81.

Description: Evolute compressed shell characterized by flattened sides, a whorl section which is from subrectangular in the inner whorls to almost sub-quadrate in the outer whorls. The wide keeled venter varies from tabulate not sulcated in the inner whorls to rounded without a sharply delimited ventral area in the outermost whorl. The umbilical edge is rounded and the umbilical wall is high and almost vertical. The sinuous ribs are fine, spaced, retroverted, usually bifurcating, rarely trifurcating, and almost faded in the proximal segment, where occasionally some gentle reliefs and dips occurs. The ribs are characterized by an almost straight (not angled backward) short proximal segment and by a moderate projection on the ventro-lateral edge. We count 60 ribs in the last whorl of the phragmocone. The little frilled suture show the E lobe shorter than L lobe, which is long with lanceolate accessory lobes. The U 2 lobe is narrow and about the half length of L. The U 3 lobe is shorter and placed on the umbilical wall. The ES saddle is gently slanting, twice as wide as the LS 1 saddle and it shows two additional lobes.

Paratypes: The paratypes have an essential uniformity with the species features for the shell coiling, venter, ornament and suture. Nevertheless, some differences can be observed in the whorl section for a more or less flattened appearance, for a more o less high and vertical umbilical wall. The not bedded paratype MSA193 shows single ribs in the innermost whorls and the paratypes MSA113 has finer and denser ribs, mainly in the inner whorls .

Remarks and comparative diagnosis: The ornament of H. calamantis remind that Hildaites subserpentinus (with reference to BUCKMAN’ s holotype only), but it differs chiefly for the wider tabulate and rounded venter, for rib-density and usually bifurcating ribs. The shell size and the occurrence are very unlike too. It is possible, however, a descent of H. calamantis from the forms of the gr. H. subserpentinus .

Occurrence: Uppermost Striatus zone and lower