Irinoceras minutum, Korn & Bockwinkel & Ebbighausen & Klug, 2003

Korn, Dieter, Bockwinkel, Jürgen, Ebbighausen, Volker & Klug, Christian, 2003, Palaeobiogeographic and evolutionary meaning of an early Late Tournaisian ammonoid fauna from the Tafilalt of Morocco, Acta Palaeontologica Polonica 48 (1), pp. 71-92 : 79-80

publication ID	https://doi.org/ 10.5281/zenodo.13272527
persistent identifier	https://treatment.plazi.org/id/03BE87DE-5A78-FFCE-FCF8-FAD275F6FD17
treatment provided by	Felipe
scientific name	Irinoceras minutum
status	sp. nov.

Treatment

Irinoceras minutum View in CoL sp. nov.

Figs. 11G, H View Fig , 14 View Fig , 15 View Fig .

Derivation of name: After the small conch, unlike the type species.

Holotype: Specimen MB.C.3916 (coll. Ebbighausen), Fig. 11H View Fig .

Type locality and horizon: Taouz, Jebel Ouaoufilal, locality A east of Ksar Bouhamed (Tafilalt, Morocco); Oued Znaïgui Formation, early Late Tournaisian.

Material.— 17 specimens, mostly fragmentarily preserved, 5 to 24 mm in diameter.

Diagnosis.—Small−sized Irinoceras with pachyconic conch between 8 mm and 15 mm diameter (ww/dm 0.60 to 0.65). Umbilicusat8mmdiameterslightlyopened(uw/dm0.10)and almost closed at 16 mm diameter. Steinkern with weak constrictions but otherwise smooth. Suture line with V−shaped, almost symmetrical adventive lobe.

Description.—All growth stages are very similar ( Fig. 14 View Fig ). Only the width of the umbilicus changes, juveniles show a narrow opening, but in adults the umbilicus is punctiform. The steinkern is smooth except for very weak constrictions which are irregularly arranged with a low projection over the flank and a rather deep ventral sinus.

As it is characteristic for Irinoceras , the external lobe is bulb−shaped with strongly sinuous flanks, followed by an asymmetrical, ventrally inclined ventrolateral saddle and by an almost symmetrical adventive lobe ( Fig. 15 View Fig ). As the holotype MB.C.3916 shows, the V−shaped adventive lobe is almost symmetrical with a gently curved ventral flank ( Fig. 15A View Fig ) .

Dimensions.—(in mm). Comparisons.—Inadequate knowledge of some Irinoceras species makes comparison between the species difficult. The majority of species, such as I. arcuatum Ruzhencev, 1947 , I. ornatissimum (de Koninck, 1881) , I. latecostatum ( Nicolaus, 1963) , I. schulzei ( Kullmann, 1963) , and I. stevanovici ( Kullmann, 1962) possess coarse growth lines or riblets. As far as the sutures are known from these species, the adventive lobe is asymmetrical, with a concave dorsal flank, and thus different from I. minutum sp. nov. I. altayense Wang, 1983 , I. romingeri ( Winchell, 1862) , I. tuba Campbell et al., 1983 , and I. weyeri Work and Nassichuk, 2000 do not have constrictions. I. bamberi WorkandNassichuk,2000 hasasimilar suture line and also constrictions, but the whorl cross section is almost circular and widest in the midflank area, in contrast to I. minutum sp. nov. where the conch is thickest near the umbilicus.