Pleuroceras solare solitarium ( Simpson, 1855 )

Bardin, Jérémie, Rouget, Isabelle & Cecca, Fabrizio, 2013, Late Pliensbachian (Early Jurassic) ammonites from Lac de Charmes (Haute-Marne, France): Systematic, biostratigraphy and palaeobiogeography, Geodiversitas 35 (2), pp. 309-334 : 326

Pleuroceras solare solitarium ( Simpson, 1855) ( Table 3)

Ammonites solitarius Simpson, 1855: 83 ; 1884: 133.

Paltopleuroceras solitarium – Buckman 1912: pl. 52.

? Amaltheus solitarius – Frentzen 1937: pl. 6, figs 8-11.

? Amaltheus solitarius var. tuberculata – Frentzen 1937: pl. 6, figs 12, 13.

Pleuroceras solare var. solitarium – Howarth 1958: 31, pl.5, fig. 10. —? Bourdenet 1964: pl. 1, fig. 5.

TYPE MATERIAL. — Ľe holotype (Whitby museum, WHITM:WM500) described by Simpson (1855: 93) is the specimen figured by Buckman (1912: pl. 52).

SPECIMEN AVAILABLE. — UPMC-203.

STRATIGRAPHICAL DISTRIBUTION. — Apyrenum subchronozone. Haute-Marne: bed 16a.

GEOGRAPHIC DISTRIBUTION. — Eastern France, Franche- Comté ( Bourdenet 1964) and Haute-Marne (this work); North-West Germany ( Jordan 1971); South-West Germany ( Frentzen 1934); England ( Howarth 1958); Morocco, Moyen-Atlas ( Morard 2004).

DESCRIPTION

Ľe shell is evolute with a whorl section higher than large. Ľe distinction of the ventro-lateral edge can occur late in the ontogeny and be slightly pronounced. Whorl section is trapezoid: whorl breadth on ventro-lateral edges is inferior to the one on dorso-ventral edges. Small tubercles can be observed up to a diameter of 20 mm. Ribs are sharp-raised.

DISCUSSION

Our specimen can be identified as P. solare solitarium because it shows tubercles in the inner whorls and a decreasing rib density along the growth. However, first, its whorl section is not as high as specimens undoubtedly attributed to P. solare solitarium ; second, rib density is intermediate between P. solare and P. spinatum . Tubercles are reduced starting from a diameter of 40 mm. Ľe identification problem is similar to the one discussed for A. margaritatus s.s. and A. gibbosus . It is necessary to study the extension of these ontogenetic stages to confirm the existence of different morphological taxa ranked at the species level or higher. Few specimens of this taxon have been found ( Simpson 1855; Buckman 1912; Frentzen 1937; Howarth 1958; Bourdenet 1964). Because of its uncertain identification, this specimen has not been taken into account for the biostratigraphic discussion.