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Which conodont fossil marks the formal boundary between the Cambrian and Ordovician systems?
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Cambrian Period
Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Cambrian Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.
The formal boundary between the Cambrian and Ordovician systems is defined by a global stratotype section and point (GSSP) that coincides with the first appearance of the conodont Iapetognathus fluctivagus. This boundary marks the base of the Tremadoc Series within the Ordovician System.1