Gatunek typowy
Polygnathus nodocostata Branson & Mehl, 1934 from the Famennian at Dixie or Noel (not specified) of Missouri 

Opis

Platform of P1 elements with tubercles tending to be arranged in ridges parallel to the blade, other elements robust, similar to those of Mehlina.

That Polynodosus is a derivative of Mehlina is suggested not only by the similarity of their apparatuses, in fact quite generalized, but also by the common development of a peniculus in at least some species (P. nodoundatus and P. diversus). There are at least four separate lineages within the genus. The least derived is represented by P. transitus and P. lauriformis, with relatively small and simple platform. In the lineage of P. confluens → P. triphyllatus the platform is extensive, and develops a constriction at mid-length. Even earlier in ontogeny the platform in the P. diversus → P. nodoundatus lineage originated. P. perplexus may or may not be a continuation of the latter, but the transition has not been traced. Probably it gave rise to Hemilistrona, in which an elaborate platform developed in the P1 elements. Late members of Polynodosus are almost homeomorphic to Polygnathus and they were earlier believed to originate from that lineage of ancient platform-bearing polygnathids.

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.