Early faunas with Watsonella crosbyi with or without Aldanella spp. have been equated with the Siberian Tommotian Stage (uppermost Terreneuvian) and used to define a proposed Cambrian Stage 2 base. Much earlier Terreneuvian occurrences are now shown by recovery of these micromolluscs below the I’ carbon excursion in the Siberian ‘Nemakit-Daldynian’ Stage and comparable δ13C excursions in the middle Meishucunian (China) and middle Chapel Island Formation (Avalonia). This δ13C excursion, a reliable Stage 2 marker, lies in a c. 10 Ma interval in the Cambrian Radiation in which long-ranged small shelly fossil taxa provide limited biostratigraphic resolution.
