Hildaites wrighti SPATH, 1913

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 : 95-96

Hildaites wrighti SPATH, 1913

Pl. I, fig. 1a-b; Fig. 6, A-B

?1870. Ammonites radians REINECKE. - MENEGHINI, pl. 11, fig. 7.

1884. Harpoceras normaniaum (D’ ORBIGNY) . - WRIGHT, pl. 83, figs. 1-2 (holotype).

1913. Protogrammoceras wrighti SPATH , p. 553 (nom. nov. holotype).

?1969. Protogrammoceras sp. , PINNA, pl. 4, fig.6.

?1980. Hildaites striatus GUEX. - WIEDENMAYER, pl. 32, figs. 1-5.

1992. Hildaites wrighti SPATH. - HOWARTH, pl.30, figs. 7a-b (holotype).

?2001. Hildaites wrighti SPATH. - MACCHIONI, pl. 6, fig. 14.

?2002a. Hildaites wrighti SPATH. - MACCHIONI, fig. 4.9.

?2006. Hildaites wrighti SPATH. - BÉCAUD, pl. 32, fig. 1.

Material: Only one medium sized specimen MSA 60 with the body chamber partly preserved and the shell strongly encrusted by pyrite, coming from Marconessa quarry.

Diagnosis: Moderately evolute and compressed shell, almost elliptical whorl section, narrow and gently bisulcate or tabulate keeled venter, high almost vertical umbilical wall in the outer whorls and rounded umbilical edge. The venter is gently bisulcate with a strong and raised keel. The fine, dense and gently sigmoidal ribs start gently backward from the umbilical wall and they end moderately projected on the ventro-lateral edge.

Description: Compared to the holotype refigured by HOWARTH (1992, pl. 30, figs. 7a-7b) our specimen seems to have a more compressed whorl section and lesser falcate ribs. HOWARTH (1992) states that the holotype has « a narrow tricarinate-bisulcate venter », but we think that this statement overemphasizes the same HOWARTH’ s figure (7b), which like our specimen really shows the weak sulci jointed with a strong and raised keel, which also shows a narrow and gently bisulcate venter in the fragmocone and a narrow and flattened venter in the body chamber. HOWARTH has not provided a draw or description of the suture line of SPATH’ s holotype. Our specimen has a simple not jagged suture, with a wide L lobe and moderately developed umbilical lobes.

Discussion and comparative diagnosis: HOWARTH (1992) inferred that WRIGHT’ s holotype, which is the only sample collected in Britain, comes from Somerset (Ilmister, Barrington) and probably it was found in the Fish and Insect Bed, which is Exaratum subzone, Falciferum zone in age. Contrary to HOWARTH’ s (1992) opinion we think that H. wrighti is not a synonym of Hildaites striatus GUEX, 1973 , because the latter shows lesser sigmoidal, finer and denser ribs, bundled or bifurcating near the umbilical wall with typical streaking appearance as well as a narrower and not sulcated venter with a thin keel. On the other side, H. wrighti shows a bisulcate venter with strong keel and usually single ribs. Besides, H. striatus has a more compressed and evolute shell than H. wrighti , whose umbilical wall is high and rounded, not sloped and flattened as that of striatus . Consequently, we cannot share HOWARTH’ s opinion. The Italian specimens figured by MENEGHINI (1870, pl. 11, fig. 7), ZANZUCCHI (1963, pl. 18, figs. 1-6) and PINNA (1969, pl. 1, fig. 16) have an uncertain taxonomy, as well as the little and badly preserved small sized fragment of the GEMELLARO’ s collection, recently revisioned by MACCHIONI (2002b, p. 147). However, they have not stratigraphical recording. We also doubt whether to ascribe the specimens figured by WIEDENMAYER (1980, pl. 32, figs. 3-5) to H. wrighti .

Occurrence: HOWARTH (1992) believes that the holotype occurs in the Exaratum subzone (lower Falciferum zone), thus it should be the earliest occurrence of Hildaites in Britain. However, the Apennines specimen occurs in the early Striatus zone.