Dimorphism and evolution of the goniatite Tornoceras in the Famennian of the Holy Cross Mountains
Henryk Makowski
A cephalopod limestone intercalation in the Early Farnennian Łagów beds of Janczyce (eastern Holy Cross Mountains, Poland) contains, in each of its five layers, abundant fossil assemblages of goniatites. The lineage of Tornoceras is
especially well represented there. It starts from typical T. jrechi with rounded venter and ends in T. sublentiforme with sharp-edged venter. A bed-by-bed biometrical study has shown a bimodal size frequency distribution of conchs in
each layer which is interpreted as sexual dimorphism. T. frechi parvurn subsp. n. and T. subacutum sp. n., are proposed new, forms that represent successive comecting links within the lineage.
Key words: ammonites, Late Devonian, Poland, evolution, sexual dimorphism.
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