Oregonites cf. imlayi Wiedenmayer, 1980

Seyed-Emami, Kazem, Fürsich, Franz T., Wilmsen, Markus, Majidifard, Mahmoud R. & Shekarifard, Ali, 2008, Lower and Middle Jurassic ammonoids of the Shemshak Group in Alborz, Iran and their palaeobiogeographical and biostratigraphical importance, Acta Palaeontologica Polonica 53 (2), pp. 237-260 : 248

Oregonites cf. imlayi Wiedenmayer, 1980

Fig. 4J.

Material.—A fragmentary inner whorl with a small portion of the body−whorl, starting at a diameter of ca. 24 mm, from Shahmirzad (050510−9).

Dimensions (in mm)

Specimen D U H W

050510−9 20 ~50 30 42

Description.—The small specimen is evolute, tricarinate−bisulcate with a depressed, broad−elliptical whorl cross−section and a strong keel bordered by rather deep sulci. The strong and slightly rursiradiate ribs start irregularly paired at the umbilical margin. On the venter, the ribs bend forward and fade before reaching the sulci.

Discussion.—The evolute specimen resembles Oregonites imlayi Wiedenmayer, 1980 . Oregonites differs from the similar genus Fontanelliceras (Fucini, 1931) by more depressed whorls, a distinctly tricarinate−bisulcate venter and paired ribs.

Stratigraphic and geographic range.—Shahmirzad, level II. Oregonites is a very rare taxon, being known so far only from the Late Pliensbachian of the Mediterranean area ( Wiedenmayer 1980) and North America ( Imlay 1968; Smith and Tipper 1996).