(1993) considered the upper part of the Acerocarina Superzone an equivalent of the Cordylodus proavus
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.