Merocanites Schindewolf, 1922

Genus Merocanites Schindewolf, 1922 View in CoL

Remarks

The co-occurrence of Merocanites and Goniatites has likely not been previously reported. Species of Merocanites are commonly found alongside much older ammonoid genera such as Ammonellipsites Parkinson, 1822 and Muensteroceras Hyatt, 1884 at the Tournaisian-Viséan boundary or slightly younger strata. They are particularly well known from Ireland ( Foord 1900), northern England ( Riley 1996), Belgium ( de Koninck 1880), the Rhenish Mountains and the Harz ( Holzapfel 1889; Schindewolf 1951; Korn 2006), the Cantabrian Mountains ( Kullmann 1963), the Montagne Noire ( Böhm 1935; Korn & Feist 2007), the Holy Cross Mountains in Poland ( Dzik 1997), the Tien Shan in Kyrgyzstan ( Popov 1968) and the Mouydir in Algeria ( Ebbighausen et al. 2010).

Another unusual fact is the remarkable size of the material from Gara el Itima. Specimen MB.C.32199.2 is a fragment of a phragmocone with a whorl height of over 70 mm. This suggests that the conch, including the body chamber, had a diameter of approximately 360 mm. Large specimens of Merocanites have so far been known from early Viséan strata. Holzapfel (1889: pl. 5) illustrated a specimen of “ Prolecanites ceratitoides von Buch ” (= Merocanites applanatus Frech, 1899 ) nearly 200 mm in size and mentioned even larger specimens ( Holzapfel 1889: 44). This material originates from the ‘Erdbach Limestone’ of the Kramberg near Erdbach in the Rhenish Mountains. Based on conodonts, this rock can be assigned to the early Viséan ( Krebs 1968).

Pareyn (1961: pl. 6) illustrated a specimen of Merocanites ogivalis Pareyn, 1961 with a phragmocone diameter of nearly 200 mm, belonging to a conch with a diameter of almost 400 mm. This specimen came from the ‘Série de Mazzer-Akacha’ in the Saoura Valley of western Algeria. This assemblage can also be placed in the late Viséan based on the conodont fauna ( Nemyrovska et al. 2006: 364).

In contrast, the representatives of Merocanites from the Tournaisian-Viséan boundary are often smaller. Merocanites merocanites Ebbighausen, Korn & Bockwinkel, 2010 from the Dalle à Merocanites of Timimoun in Algeria reaches a conch diameter 70 mm ( Ebbighausen et al. 2010: 199), M. djaprakensis Librovitch, 1927 attains 120 mm ( Popov 1968: 79) and M. applanatus from the ‘Erdbach Limestone’ of the Harz reaches a conch diameter about 150 mm (Korn 2006: 155). An exception is Merocanites quadrilobus Riley, 1996 from the Leagram Mudstone Member; the holotype has a phragmocone whorl height of 52 mm, corresponding to a total conch diameter of more than 250 mm ( Riley 1996).