Accardia aff. diadematoides ( Mayer, 1871 )

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 : 255

Accardia aff. diadematoides ( Mayer, 1871)

Fig. 6N.

1871 aff. Ammonites diadematoides ; Mayer 1871: 243, pl. 8: 9. 2006 aff. Accardia diadematoides ( Mayer, 1871) ; Seyed−Emami et al. 2006: 269, figs. 5/8a, b, 16a, b (with synonymy).

Material.—A specimen preserved one side from Sharif−Abad (050512−11/10).

Dimensions (in mm)

Specimen D U H W

050512−11/10 57 35 39 ~39

76 34 39 ~32

Description.—Coarsely ribbed Hammatoceratinae with a high hollow−floored keel. The whorl cross−section on the inner whorls is broad−ovate, becoming triangular high−ovate at the last preserved whorl. On the inner whorls the ribbing consists of short and blunt primaries ending in strong tubercles (about 15 tubercles at D = 50 mm). From a diameter of 50 mm onwards, the nodes give way to short, strong, and radiate primaries, often bifurcating below the mid−flank into slightly sinuous secondaries. On the venter the ribs curve slightly forward and end at the keel.

Discussion.—The figured specimen matches well the original of Mayer (1871) figured by Rieber (1963: pl. 8: 5, 7). Compared with a larger specimen from the Shemshak Group of the Tazareh section, described by Seyed−Emami et al. (2006), the present specimen has a greater number and more densely spaced tubercles.

Stratigraphic and geographic range.—Sharif−Abad, level G. Late Aalenian, Otoceras concavum Zone.