Imitoceras Schindewolf, 1923

Korn, Dieter & Weyer, Dieter, 2023, The ammonoids from the Gattendorfia Limestone of Oberrödinghausen (Early Carboniferous; Rhenish Mountains, Germany), European Journal of Taxonomy 882, pp. 1-230 : 108

Genus Imitoceras Schindewolf, 1923

Type species

Ammonites rotatorius de Koninck, 1844: 565 ; original designation.

Genus diagnosis

Genus of the Imitoceratinae with large discoidal conch, reaching a diameter of 150 mm. Conch subinvolute or subevolute in early juveniles; umbilicus closes completely early in ontogeny. Coiling rate moderate to high (WER = 1.70–2.20). Suture line with slightly pouched, often very narrow external lobe; ventrolateral saddle strongly asymmetric and ventrally inclined; adventive lobe usually asymmetric and V-shaped with convex ventral flank and concave dorsal flank; adventive lobe much deeper than the external lobe (after Korn et al. 2010b, modified).

Genus composition

Central Europe (de Koninck 1844; Schindewolf 1926a): Ammonites rotatorius de Koninck, 1844 ;? Imitoceras Wurmi Schindewolf, 1926 .

North Africa ( Bockwinkel & Ebbighausen 2006; Korn et al. 2010a, 2010b): Imitoceras oxydentale Bockwinkel & Ebbighausen, 2006 ; Imitoceras altilobatum Korn, Ebbighausen & Bockwinkel, 2010 ; Imitoceras dimidium Korn, Bockwinkel & Ebbighausen, 2010 ; Imitoceras strictum Korn, Bockwinkel & Ebbighausen, 2010 .

Tibet ( Liang 1976): Imitoceras orientale Liang, 1976 ; Imitoceras xizangense Liang, 1976 .

British Columbia ( Work et al. 2000): Imitoceras tardum Work & Nassichuk in Work, Nassichuk & Richards, 2000.

American Midcontinent ( Hall 1860; Winchell 1862; Miller 1891; Miller & Gurley 1896; Smith 1903; Miller & Collinson 1951; Gordon 1965): Goniatites Ixion Hall, 1860 ; Goniatites propinquus Winchell, 1862 ; Goniatites indianensis Miller, 1891 ; Goniatites Jessiae Miller & Gurley, 1896 ; Aganides discoidalis Smith, 1903 ; Imitoceras abundans Miller & Collinson, 1951 ; Imitoceras brevilobatum Miller & Collinson, 1951 ; Imitoceras lentiforme Miller & Collinson, 1951 ; Imitoceras sinuatum Gordon, 1965 .

Remarks

Many of the species of Imitoceras require revision; it is not clear if all the species listed above really belong to the genus. Imitoceras possesses a set of sutural characters that clearly separates it from other genera, (1) the slightly pouched external lobe, (2) the strongly asymmetric, ventrally inclined ventrolateral saddle and (3) the asymmetric adventive lobe. Irinoceras has a much stronger pouched external lobe, and the possibly ancestral genus Nicimitoceras has a lanceolate external lobe. Triimitoceras has a rather symmetric adventive lobe and is also distinguished from Imitoceras by its conch ontogeny with a low coiling rate ( Korn et al. 2010b).