Abstract

Shelly faunas and phytoplankton from Lower Cambrian (Tommotian) strata within and outside the type area in Siberia indicate that the Tommotian Stage is younger than previously believed. Deposits referred to the Tommotian Stage in Siberia are, in part, time equivalent to the Talsy (Lukati) Horizon in the East European Platform, which has yielded trilobites and is correlated with the Schmidtiellus mickwitzi trilobite zone in Baltoscandia.

Published micropaleontological data seem to indicate that the Yudomian Stage preceding the Tommotian may also belong to the Cambrian System. The demonstrated contemporaneity of Tommotian small shelly faunas with the trilobites could result in a revision of models dealing with the early radiation of metazoan phyla, speciation, and skeletonization.

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