Gatunek typowy
Protornoceras polonicum Dybczyński, 1913 from the Famennian of Kielce.

Opis

Diagnosis. — Simplified suture with a very shallow flank lobe and usually almost straight course of its ventrolateral part; weak ventro-lateral vaultings may develop in the septum; open umbilicus. 

Remarks. — This seems to be a separate branch of the tornoceratids evolving towards the clymenoid appearance of the conch and suture. Various forms occur together in the black shale with pyritized ammonoids at Kowala, which suggests their immigration to the Holy Cross Mountains area with the sea transgression of the C. marginifera Zone (perhaps at its later stage). Probably the least derived of them is P. aphyllitiforme, with almost closed umbo, the most derived is P. mirabile. There was proposed the genus Tornia for the latter. Perhaps it would be truly reasonable to put the protornoceratids with narrow and wide umbilicus into different genera, but the type species of both Protornoceras and Tornia are widely umbilicate. Because of the high population variability, their separation seems superfluous. The phylogenetically closest Kirsoceras differs in the subventral position of the siphuncle. 

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.