Holcophylloceras polyolcum ( Benecke, 1866 )

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 : 516

Holcophylloceras polyolcum ( Benecke, 1866) ( Fig. 4C )

Ammonites polyolcus Benecke, 1866: 182, pl. 8, figs 1, 2.

Phylloceras zignodianum – Gemmellaro 1871: 251; 1876: 47, pl. 9, figs 1, 2 (non Phylloceras zignodianum d’Orbigny, 1847 ).

Holcophylloceras polyolcum – Joly 2000: 101, textfig. 208, pl. 25, fig. 4, synonymy list. — Pavia 2002: 57, fig. 24c, d.

MATERIAL EXAMINED. — MI4N 8d/1, MI4N 8c/2, MI4W 8b/c/1, MI4W 8top/1. Specimens determined as H. cf. polyolcum due to insufficient preservation: MI4N 6e/1, MI4N 8 “top”/4.

STRATIGRAPHIC DISTRIBUTION. — This species is rather common from bed 8c to 8d of section Monte Inici East, which have been assigned with doubt to the Hauffianum Subzone of the Late Oxfordian Bimammatum Zone. The species probably appears in a layer because a specimen identified as H. cf. polyolcum has been found in bed 6e, which has been assigned to the Transversarium Zone. This species is commonly reported from Lower Kimmeridgian to Tithonian strata ( Sarti 1993). The studied material suggests for this species an earlier appearance than previously tought.

DESCRIPTION

Compressed, involute shell with elliptical whorl section. The umbilicus of this species is relatively wide when compared with the general phylloceratid morphology. Seven to nine furrows per whorl spring from the inner (dorsal) part of the umbilical margin. These furrows are radiate or prorsiradiate in the lower half of the flank but in a point roughly located slightly above the mid flank, they become shallower and larger; in the upper third of the flank the furrows are deeply excavated and rursiradiate. A ridge is developed on the adoral edge from the upper fourth of the flank and on the venter, where the furrows are adapically convex. No shell remains are preserved. Measurements: see Table 3.

DISCUSSION

The first report of this species from beds older than the basal Kimmeridgian ( Cecca et al. 2001) can cast doubts on the identification of the studied specimens. They have been assigned to H. polyolcum because of their more numerous furrows, with a less sharply falcoid aspect than H. zignodianum (d’Orbigny, 1848) and H. mediterraneum ( Neumayr, 1871) (the latter can be considered a synonym of the former as summarised by Pavia 2002).

Suborder AMMONITINA Hyatt, 1889

Figures

FIG. 4. — A, Calliphylloceras benacense (Catullo,1847),specimen MI4N 8b/2 from bed 8b of section Monte Inici East;B, Sowerbyceras tortisulcatum (d’Orbigny,1841),specimen MI4N 6c/1 from bed 6c of section Monte Inici East;C, Holcophylloceras polyolcum (Benecke, 1866), specimen MI4W 8b/c/1 from bed 8c of section Monte Inici East; D, Tornquistes (T.) cf. romani (Douvillé, 1912), specimen MI3 9/7 from bed 9 of section Castello Inici; E, Streblites frotho (Oppel, 1863), specimen MI4N 8b/1 from bed 8b of section Monte Inici East. All figures natural size. Arrows indicate the beginning of the body chamber.