Opis

Diagnosis. — Large protoconch 0.7 to 1.0 mm in width; suture with pointed lateral and trifid dorsal lobes; conch aperture with oblique convex profile; relatively low whorl expansion rate.

Remarks. — Cheiloceras polonicum Sobolew, 1912 from the black clymeniid limestone at Łagów-Dule shows rare internal thickenings and the external part of its suture of Prionoceras morphology. It is stratigraphically transitional between the lowest occurrence of the true Prionoceras and the typical cheiloceratids. Unfortunately, the internal part of its suture remains unknown and no other specimen has been collected.
The characteristic barrel-shaped protoconch of unusually large size emerged together with first conchs of the Prionoceras morphology at Jabłonna  to continue into the Carboniferous. Probably this is the most characteristic evolutionary novelty (synapomorphy) do define the family, although its knowledge if far from being satisfactory.

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.