A chitinozoan morphological lineage and its importance in lower silurian stratigraphy

Margachitina margaritana is a distinctive, chain-forming chitinozoan taxon of the uppermost Telychian Stage (Llandovery Series) to lower Homerian Stag e (Wenlock Series). M. margaritana is shown to be the end member of a morph ological lineage that developed from Calpichitina densa via the intermediat e Margachitina banwyensis sp. nov. A local M. banwyensis Biozone, which cor relates with the upper lapworthi graptolite Biozone, is proposed for the Ba nwy River section. The morphological lineage described provides a tool for the enhanced subdivision of the uppermost Llandovery Series, which may prov e global in extent. This research suggests also that the base of the Wenloc k Series may correlate with a level below the centrifugus graptolite Biozon e and it also brings into question the systematic status of Calpichitina an d Margachitina, although both genera are retained herein.