Stage 2 of the Cambrian is the unnamed upper stage of the Terreneuvian series. It lies on top of the Fortunian and below Stage 3 of the Cambrian. It is commonly referred to as the Tommotian, after the Cambrian stratigraphy of Siberia. Both the upper and lower boundary have not been clearly defined yet by the International Commission on Stratigraphy. Proposals for the lower boundary are the appearance of Small Shelly Fossils, an archaeocyathid  species or the mollusc Watsonella crosbyi around million years ago. The proposed upper boundary might be the first appearance of trilobites around million years ago.