Paradumortieria elmii Seyed−Emami, 2008

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 : 251

Paradumortieria elmii Seyed−Emami sp. nov.

Fig. 5A–D, Q.

1985 Dumortieria aff. schaireri Seyed−Emami, 1985 ; Seyed−Emami and Nabavi 1985: 260, fig. 6a–c.

Type material: The holotype is a complete microconch form with lappet (050511−3/1; Fig. 5A 1 , A 2). Paratypes: specimens 050511−3/2 and −3/6. Hypotype: 14−2−3 (originally figured as Dumortieria aff. schaireri Seyed−Emami by Seyed−Emami and Nabavi 1985: fig. 6a–c).

Type horizon: Shemshak Group , Upper Toarcian, Pleydella aalensis Zone, Kuhe Bashm section, level V at 245 m ( Fig. 2) .

Type locality: Kuhe Bashm, 13.5 km east of Shahmirzad , about 25 km north of Semnan .

Derivation of the name: In honour of the Late Prof. Dr. S. Elmi (1936–2007)

Material.—Seven, mostly well−preserved specimens from the Kuhe Bashm section (050511−3 and earlier collections by K.S.−E.: 7−21−1, 14−2−3, 14−49).

Diagnosis.—Small, evolute microconchs with elongated lappets and rectangular to high−ovate whorl cross−section. Venter tectiform with a distinct keel. Ribbing relatively coarse, slightly flexuous, ventrolaterally strongly projecting forward. Body whorl about 3/4 of the last whorl.

Dimensions (in mm)

Specimen D U H W

050511−3/1 (holotype) 30 42 34 24 (end of body−chamber) 25 40 36 26

14−2−3 (hypotype) 27 41 36 24

7−21−1 27 41 33 23

050511−3/6 (paratype) 31 40 35 –

Description.—Small (D: 27–32 mm), evolute microconchs with rectangular to high−ovate whorl cross−section. The venter is tectiform with a distinct keel, persisting up to the end of body whorl. Ribs are slightly flexuous, relatively coarse, spaced, and projecting strongly forward ventrolaterally. Towards the end of the body whorl the ribs become finer, denser and irregularly paired. The body whorl occupies about 3/4 of the last whorl and carries elongated, spatula−like lappets.

Discussion.—The new species is intermediate between P. schaireri , P. explanata (Buckman 1904: suppl. 104, pl. 22: 28–30), and P. tabulata (Buckman 1904: suppl. 185, pl. 22: 25–27). From the closely related P. schaireri the new species differs in having coarser and wider spaced ribs. Compared to P. explanata and P. tabulata the new species is less coarsely ribbed and its final size is probably smaller. Similarly, the new taxon differs from P. tectiforme Elmi and Caloo, 1985 by its finer ribbing and distinctly smaller final size.

Stratigraphic and geographic range.—The new species was found, together with P. schaireri , P. explanata , and several specimens of the Dumortieria radiosa / moorei group, in a single concretion from Kuhe Bashm, level V.

Figures

Fig. 1. Distribution of the Shemshak Group in the central and eastern Alborz, northern Iran. 1: Position of the Shahmirzad and Kuhe Bashm−e−Dehsufian sections; 2: Position of the Sharif Abad section.