Evolutionary lineages in some Ordovician Chitinozoa

Three new species of chitinozoans are described from the Ordovician Simcoe Group in southern Ontario, Hercochitina lindsayiensis sp. nov., H. pinguis sp. nov., and H. spinetum sp. nov. In addition, two new combinations, Hercochitina concava (Finger 1978) and Hercochitina respinata (Schallreuter 1981), are proposed.

Hercochitina lindsayiensis and H. pinguis appear to be evolutionarily intermediate forms between Hercochitina respinata (Schallreuter) n. comb., and H. crickmayi (Jansonius 1964) and H. minuta (Achab 1977), respectively. This evolutionary transition is manifest as a change in surface ornamentation.

This lineage is compared with a previously described evolutionary lineage involving similar species of Belochitina and Hercochitina. Some taxonomic revisions are made on taxa in this latter lineage in which H. spinetum is an intermediate form between B. robusta (Eisenack 1959) and H. normalis (Achab 1977). This evolutionary transition also involves changes in the surface ornamentation. The genus Hercochitina is therefore diphyletic.

The known North American stratigraphic ranges of the species involved (Chazyan-Cincinnatian) are presented.