Stage 2 of the Cambrian is the unnamed upper stage of the Terreneuvian series. It lies atop the Fortunian and below Stage 3 of the Cambrian. It is commonly referred to as the Tommotian, after the Cambrian stratigraphy of Siberia. Neither the upper nor lower boundary have yet been defined 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 529 million years ago. The proposed upper boundary might be the first appearance of trilobites around 521 million years ago.
Possible candidates for a GSSP include the first appearance of Watsonella crosbyi in the Zhujiaqing Formation in Yunnan, China or the Pestrotsvet Formation near the Aldan River on the Siberian Platform.