Tommotian Stage

The Tommotian Stage is a Russian designation for the pre-trilobite portion of the Cambrian explosion. This early part of the Cambrian Period, which occurred over 500 million years ago, is characterized by the appearance of many new animal forms. While trilobites are the primary guide fossils for much of the Cambrian, the Tommotian Stage predates their widespread evolution and is instead correlated using small shelly fossils, such as mollusks and other problematic organisms. These fossils, however, are often endemic to specific regions, making intercontinental correlation challenging. The Cambrian Period itself saw significant geological events, including the formation of shallow seas and, later, widespread continental ice sheets that influenced sea levels and led to cyclic deposition.12