Late ordovician epoch
Ordovician period
Hirnantian Age

The Hirnantian

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

Paleozoic Era
   Cambrian Period
   Ordovician Period
      Early Ordovician Epoch
     Middle Ordovician Epoch
      Late Ordovician Epoch
         Sandbian Age
         Katian Age
         Hirnantian Age 
   Silurian Period
      Llandovery Epoch
         Rhuddanian Age 
         Aeronian Age 
         Telychian Age 
      Wenlock Epoch
      Ludlow Epoch
      Přídolí Epoch
   Devonian Period
   Carboniferous Period
   Permian Period



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 The traditional division of the Late Ordovician into the Caradoc and Ashgill has been replaced by a three-part division.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

  Platystrophia laticosta

Platystrophia laticosta Meek

Phylum Brachiopoda
Order Orthida
Family Plectorthidae

Maysville Group

early Hirnantian epoch - Pusgillian Age

southern USA

shell about 2 to 2.5 cm wide

More on Platystrophia (at the Union College Geology Department site)

Rafinesquina loxorhytis

Rafinesquina loxorhytis (Meek)

Phylum Brachiopoda
Order Strophomenida
Family Strophomenidae



shell about 7 cm wide

more on Rafinesquina (at the Union College Geology Department site)

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unless otherwise indicated, content by M. Alan Kazlev 1998-2002
page uploaded 8 June 2002
checked ATW040314
(original page uploaded on Kheper site 15 October 1998)

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