Gatunek typowy
Polygnathus streeli Dreesen, Dusar et Groessens, 1976 from the costatus Zone of Belgium.

Opis

S1 element with additional ventral process, P1 elements tend to develop a relatively wide, flat or inverted basal cavity delimited by an escarpment extending to the element tip.
As shown by the apparatus structure, the similarity to the Alternognathus lineage in the form of the basal cavity of P1 elements is a case of homeomorphy. Immognathus is probably a direct successor of the Ctenopolygnathus lineage and in the oldest samples (e.g., J-42) transitional morphologies of P1 elements between these genera occur, that is the platform does not reach the element tip in juveniles and the basal cavity may be rather small and narrow in the same elements. Such elements are associated (e.g., sample J-44) with S1 elements showing an additional ventral process. Notably, in the somewhat older bed 7 closely similar platform elements are associated with S1 elements of Ctenopolygnathus morphology. This suggests that an evolutionary transition is recorded in the Jabłonna section. Mature specimens of Immognathus developed asymmetry in platform shape similar to that in Polygnathus webbi. Polygnathus rarus of Baliński (1995) from the Dębnik area may be another member of this branch.

Synonimy

Zasięg czasowy

Literatura

Dzik, J. 2006. The Famennian „Golden Age” of conodonts and ammonoids in the Polish part of the Variscan sea. Palaeontologia Polonica 63, 1-359.