The Hirnantian

The Hirnantian Age of the Late Ordovician Epoch: 446 to 444 million years ago

Introduction

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 The traditional division of the Late Ordovician into the Caradoc and Ashgill has been replaced by a three-part division.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.

Marine Invertebrates