|Late ordovician epoch|
|Katian||Middle Ordovician||Late Ordovician|
The Ordovician has been quite significantly revised in recent years. The traditional division of the Late Ordovician into the Caradoc and Ashgill has been replaced by a three-part division. The first two ages of the Late Ordovician are unnamed, and are referred to as Ordovician V and VI. Sandbian is equivalent to the Early and Middle Caradoc. Ordovician VI is equivalent to the Late Caradoc and Early Ashgill. The Hirnantian, formerly a stage of the Ashgill, is now the final age of the Ordovician.
early Hirnantian epoch - Pusgillian Age
shell about 2 to 2.5 cm wide
shell about 7 cm wide
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