Ammonitina Hyatt, 1889

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 : 243

Suborder Ammonitina Hyatt, 1889 Superfamily Psiloceratoidea Hyatt, 1867 Family Echioceratidae Buckman, 1913

Genus Paltechioceras Buckman, 1927 Paltechioceras cf. oosteri (Dumortier, 1867)

Fig. 4F.

1867 cf. Ammonites oosteri ; Dumortier 1867: 164, pl. 30: 3, 4.

1977 Arnioceras mendax rariplicata Fucini ; Nabavi and Seyed−Emami 1977: 80, fig. 9 (2, 3).

1991 cf. Paltechioceras cf. oosteri (Dumortier) ; Schlatter 1991: 44, pl. 5: 8–11; text−fig. 29.

1998 cf. Paltechioceras oosteri (Dumortier, 1867) ; Blau 1998: 213, pl. 10: 14, 17, 19; pl. 14: 2.

2002 cf. Paltechioceras oosteri (Dumortier, 1867) ; Hillebrandt 2002: 107, pl. 11: 14–21.

Material.—One external mould (050510−2) and several juvenile specimens from Shahmirzad.

Dimensions (in mm)

Specimen D U H W ribs/whorl 050510−2 27 ~59 24 – 36 69−N−183b 34 58 26 26 36

Description.—The figured specimen is extremely evolute, tricarinate−bisulcate, with a nearly quadrate whorl cross−section. Ribs are strong, sharp and radiate. At the ventrolateral edge the ribs thicken slightly, bend forward and die out near the ventral grooves. In a smaller specimen (050510−3/1) the suture line is visible. It is relatively simple with minor indentations.

Discussion.—With respect to the number and coarseness of ribs, which slightly thicken towards the venter, as well as in dimensions our specimens are closely comparable with P. oosteri , especially the specimens figured by Schlatter (1991: pl. 5: 8) and Blau (1998: pl. 10: 4).

Previous records of Vermiceras and Arnioceras ( Nabavi and Seyed−Emami 1977) from the same locality and probably from the same level, are most likely misidentifications and also belong to the genus Paltechioceras . Similarly, Vermiceras scylla (Reynès, 1879) in Nabavi and Seyed−Emami (1977: 80, fig. 9/1) is probably a Paltechioceras . Except for the venter, which does not seem to be tricarinate, the latter closely resembles P. aplanatum ( Hyatt, 1889) of Schlatter (1991: pl. 7: 2).

Stratigraphic and geographic range.—Shahmirzad, level I. Paltechioceras oosteri is widely distributed in the Late Sinemurian of Europe, being also recorded from North and South America ( Hillebrandt 2002). Blau (1998: 234) recorded P. oosteri from the Paltechioceras aplanatum Subzone of the Echioceras raricostatum Zone , Upper Sinemurian (Lotharingian). This is the first record of Paltechioceras from Iran.