Euaspidoceras cf. oegir (Oppel, 1863)

Cecca, Fabrizio & Savary, Bérengère, 2007, Palaeontological study of Middle Oxfordian- Early Kimmeridgian (Late Jurassic) ammonites from the Rosso Ammonitico of Monte Inici (north-western Sicily, Italy), Geodiversitas 29 (4), pp. 507-548 : 534-536

Euaspidoceras cf. oegir (Oppel, 1863) ( Fig. 7C)

MATERIAL EXAMINED. — MI4N 6d/1.

STRATIGRAPHIC DISTRIBUTION. — The specimen has been collected in bed 6d of section Monte Inici East, assigned to the Transversarium Zone. According to Bonnot & Gygi (2001), this species occurs within the Transversarium Zone from the top of the Antecedens Subzone up to the top of the Luciaeformis Subzone. In Bert’s (2004) stratigraphic scheme this stratigraphic range corresponds to an interval spanning from the top of the Antecedens Subzone of Plicatilis Zone sensu Bert 2004 up to the top of the Luciaeformis Subzone of the Transversarium Zone sensu Bert 2004.

DESCRIPTION

The specimen is an entirely septated internal mould showing an evolute coiling. The whorl section is subquadratic, the flanks are flat. Neither the umbilical edge, nor the umbilical wall, is developed. The sculpture is made of two rows of tubercles, periumbilical and ventrolateral. The periumbilcal tubercles are rather bullae, i.e. they are shortly stretched along the height, whereas the ventrolateral tubercles have the aspect of spines. An extremely weak rib links the tubercles of the two rows. The preservation of the early whorls does not allow precise measurement of the diameter where tubercles begin. Nevertheless, the first visible ventrolateral spine occurs at a diameter of almost 16 mm, whereas the first ventrolateral bulla is visible at an approximate diameter of 18 mm. Measurements: see Table 19.

DISCUSSION

The preservation of this single specimen is far from satisfactory. However, its visible characters suggest the comparison with E. oegir . Our specimen shows, at the same diameter, close ornamental characters to the well preserved specimens of this species recently illustrated by Bonnot & Gygi (2001) and only differs because of its lower whorl height.

Euaspidoceras paucituberculatum ( Arkell, 1927) ( Fig. 11 )

Aspidoceras paucituberculatum Arkell, 1927 : pl. 2, fig. 2.

Aspidoceras (Euaspidoceras) paucituberculatum – Arkell 1940: 210, pl. 45, figs 2-5, pl. 46, figs 1-4, pl. 47, figs 1, 2, text-fig. 74, synonymy list.

Euaspidoceras paucituberculatum – Bonnot & Gygi 2001: 431, pl. 1, fig. 4.

MATERIAL EXAMINED. — MI3 8 top-9/1.

STRATIGRAPHIC DISTRIBUTION. — The specimen has been collected at the boundary between beds 8 and 9 of Castello Inici section and possibly it belongs to the very base of bed 9. This species is reported from the Middle Oxfordian Plicatilis Zone.

DESCRIPTION

Incomplete specimen of a large individual characterized by an evolute shell whose diameter could have reached almost 210 mm. The visible inner whorls are preserved as a cast while the last whorl is an inner mould. Up to a diameter of almost 22 mm the sole sculptural elements preserved are external tubercles (these corresponded to spines almost perpendicular to the flank as demonstrated by their impression on the sediment) located on the ventrolateral edge. An umbilical row of tubercles is visible at 30 mm but probably appears around 22-24 mm. The two rows of tubercles correspond to extremities of shallow ribs. The interspaces between two ribs bear fine, radial growth-lines. Between 80 and 115 mm the sculptural characteristics are poorly visible, with the exception of growth-lines that appear to be rursi-radiate on the wide, oblique, umbilical wall. The second half of the last whorl belongs to the body chamber and is characterized by spaced ribs that bear umbilical and ventrolateral tubercles.

DISCUSSION

The preservation of the studied specimen does not allow a firm identification. The succession of ornamental stages is similar to the one described by Arkell (1940: 212, 213) but in our specimen the onset of the two rows of tubercles is recorded at lower diameters. Two laevaptychi are visible at the end of the last whorl but it is difficult to state whether they belonged to this individual or not.

Figures

FIG. 11. — Euaspidoceras paucituberculatum (Arkell,1927),specimen MI3 8 top-9/1 from the boundary between beds 8 and 9 of Castello Inici section. The two asterisks indicate two laevaptychi. The arrow indicates the beginning of the body chamber. Scale bar: 5 cm.