Diagnoza

Fragments of juvenile ammonoid conchs commonly occur in samples processed for conodonts. In older samples from the Dzikowiec section they are mostly of rather generalised morphology and uniform size (Fig. 30C-E) that does not allow more precise identification, except that these are prionoceratids. In sample Dz-2L,however, there is more diversity in protoconch morphologies and along with typical prionoceratid protoconchs of significantly smaller size, possibly representing Eocanites (Fig. 30B), as well as extremely large ones, occur. The latter protoconch type is virtually indistinguishable in size and shape from that attributed to a prodromitid from the Exshaw Shale of Alberta by Schindewolf (1959) and House (1992). Only two larval septa are represented in the Dzikowiec specimen, so it is unclear whether the prodromitid subdivision of the ventral lobe was developed there. Probably not yet, as the age of the Dzikowiec sample is significantly older than the Exshaw Shale ammonoids, but phylogenetic affinity to the prodromitids seems clear. I find it also unlikely that the protoconch belonged to a genus unknown from the European or southern Chinese Tournaisian. This means that the ancestry of this still enigmatic North American lineage has to be sought among oxyconic Gattendorfia Stufe ammonoids exhibiting a tendency to subdivide the venkal lobe. At least two such forms are known: Voeringerites peracutus (Vdhringer, 1960) fiom Bed 5 at Oberrhcidinghausen (see Korn 1994), thus much older than the Dzikowiec species, and Karagandoceras? sp. n. I of Bartsch & Weyer (1988) from the S. sandbergi Zone of Thuringia, which is more or less coeval or a little older. Of similar age is also the most primitive Chinese prodromitid, Qiannites acutus Ruan, 1981. The Dzikowiec species may belong to the same lineage being somewhat older than Eoprodromites from the S. crenulata Zone of the Hannibal Shale in Missouri, the ancestor of Prodromites (Work el al. 1988).

Porównanie

Autekologia

Występowanie geograficzne

Zasięg czasowy

Materiały muzealne

Literatura

Dzik, J. 1997. Emergence and succession of Carboniferous conodont and ammonoid communities in the Polish part of the Variscan sea. Acta Palaeontologica Polonica 42, 57-170.