(1993) considered the upper part of the Acerocarina Superzone an equivalent of the Cordylodus
proavus conodont Zone.
Obolus apollinis appears in he uppermost Cambrian (Cordylodus
proavus Biozone) and occurs in abundance in the Cambrian-Ordovician boundary beds of NW Russia, forming the Obolus phosphorite deposits commercially mined near Kingisepp (Krasilnikova & Ilyin 1989).
Muller (1973) described and illustrated Cambrian (Furongian) conodonts, including Cordylodus
proavus Muller, 1959, from the uppermost part of the Mila Formation Member 4 in the Mila-Kuh section.
According to Bogolepova & Gee (2004), the Khmelev Regional Stage in the South Urals includes the upper Furongian Cordylodus
proavus Zone, whereas the Kidryas Regional Stage corresponds to the lower Tremadocian (Fig.