Gatunek typowy
Alternognathus regularis Ziegler et Sandberg, 1984 from the Famennian Three Forks Formation of Montana. 

Opis

Diagnosis. — P1 element with platform developing transverse ridges almost at the same level as the tips of nearby denticles of the blade, distinct shallow larval basal cavity of fusiform outline.

Remarks. — The oldest occurrence of the Alternognathus lineage in the Holy Cross Mountains is sample Md-2 from Miedzianka, where it co-occurs with C. (C.) inflexoidea, thus older than the entry of P. trachytera. P1 elements in this sample usually show very weak development of the platform, which remains incipient even in large specimens. A platform-icrion developed stronger on one side of the blade and axial symmetry may be involved there. In bed 24 at Jabłonna the lineage co-occurs with P. trachytera, but the platform remains relatively narrow. Mature elements with very wide platform occur abundantly in sample Wzd-10 at Ściegnia. Juveniles are virtually missing there. It remains thus undecided whether the difference in width of the platform between samples results from evolution or only expresses differences in population dynamics.
The P2 elements of Alternognathus differ from those of associated Pseudopolygnathus, Dasbergina and Pandorinellina in a significantly more prominent dorsal process. The differences between these genera in the rest of the apparatus are minor and it is hardly possible to separate them in samples where they occur in similar numbers.

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.