Amaltheus subnodosus ( Young and Bird, 1828 )

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 : 246

Amaltheus subnodosus ( Young and Bird, 1828)

Fig. 4E.

1828 Ammonites subnodosus ; Young and Bird 1828: 258, pl. 13: 3. 1958 Amaltheus subnodosus (Young and Bird) ; Howarth 1958: 8, pl. 2:

11–18; text−fig. 6 (with synonymy).

Material.—One fairly well preserved specimen with parts of the body whorl (050514−6/1) and two fragments (050514− 6/4, 050514−6/9) from Shahmirzad.

Dimensions (in mm)

Specimen D U H W ribs/whorl

050514−6/1 23 37 39 ~35 15 (end of phragmocone)

31 38 35 ~24 18 (on the body whorl)

Description.—The figured specimen is a rather small, evolute and coarsely ribbed Amaltheus with elliptical whorl cross−section and a prominent crenulated keel. On the inner part of the flank ribs are strong, radiate−straight, with tubercles about the mid−flank. Near the venter, the ribs bend forward, become fainter, and bifurcate indistinctly. On the body chamber, the ribbing is slightly denser and less coarse and the tubercles gradually fade.

Discussion.—The described specimen matches well the neotype of A. subnodosus , designated by Howarth (1958: pl. 2: 11). Another very similar specimen is A. margaritatus forme subnodosus of Meister (1988: pl. 1: 6).

Stratigraphic and geographic range.—Shahmirzad, level II. A. subnodosus is reported to occur in the lower part of the Amaltheus margaritatus Zone ( A. subnodosus Subzone ).