Nebrodites, Burckhardt, 1910

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 : 526

Nebrodites aff. contortus ( Neumayr, 1871) ( Fig. 8A, B )

MATERIAL EXAMINED. — MI4N 8d/2.

STRATIGRAPHIC DISTRIBUTION. — The specimen has been collected in bed 8d top of section Monte Inici East, which has been assigned with doubt to the Hauffianum Subzone of the Late Oxfordian Bimammatum Zone.

DESCRIPTION

Evolute, serpenticone, shell. Only the last whorl is preserved. The whorl section is elliptical, with flat to slightly rounded flanks and rounded venter. The umbilical edge is rounded and no umbilical wall is developed. The ornamentation consists of numerous radial to slightly prorsiradiate single and biplicate ribs which branch in the upper third of the flank. The ribs are attenuated on the venter. Two deep and oblique constrictions are visible in the last whorl: they are adorally bounded by strong, swollen, ribs. A third, final constriction precedes the mouth, which is marked by an abrupt lateral expansion of the whorl that acquires a subcircular section. Measurements: see Table 12.

DISCUSSION

This single specimen shows the typical characters of the genus Nebrodites (i.e. evolute coiling, biplicate ribs branching in the upper third of the flank, deep constrictions and attenuated ribbing on the venter), whose first appearance is generally recorded at the beginning of the Kimmeridgian. The morphological characters of this specimen are clear-cut and certainly do not allow its assignment to the genus Passendorferia , thus suggesting the appearance of the genus Nebrodites since the upper part of the Bimammatum Zone. This supports the recent reappraisal of the age of the type level of the species Nebrodites macerrimus by Schweigert & Callomon (1997).

Neumayr (1871: 369, pl. 21, fig. 1) described the species Simoceras contortum , which shows Nebrodites characters, from limestones of an unknown Oxfordian horizon. The specimen found at Monte Inici differs from this species because of its narrower whorls, the higher position of the point of bifurcation (upper third of the flank instead of mid flank) and, probably, the lower number of constrictions.

Figures

FIG. 8. — Nebrodites aff. contortus (Neumayr, 1871), specimen MI4N 8d/2 of bed 8d top of section Monte Inici East; A, lateral view; B, ventral view; C, Nebrodites passendorferiiforme Caracuel, Olóriz & Rodriguez-Tovar, 1999, specimen MI4W 10top/2 from bed 10 of section Monte Inici East; D, Nebrodites cf. hospes (Neumayr, 1873), specimen MI4W 10top/3 from bed 10 of section Monte Inici East; E,?“Passendorferia” aff. teresiformis Brochwicz-Lewinski, 1973, specimen MI4N 8 “top”/5 from bed 8d of section Monte Inici East. All figures natural size. Arrows indicate the beginning of the body chamber.