Late Ordovician

The Late Ordovician, also called the Upper Ordovician by geologists, is the third epoch of the Ordovician period.^[1]

At this time Western and Central Europe and North America collided to form Laurentia, while glaciers built up in Gondwana, which was positioned over the South Pole. This caused a drop in global temperatures, resulting in "ice house" conditions.^[2]

For most of this time life continued to flourish, but at and near the end of the period there were mass-extinction events that seriously affected planktonic forms like conodonts, graptolites, and some groups of trilobites (Agnostida and Pytchopariida, which completely died out, and the Asaphida which were much reduced). Brachiopods, bryozoans and echinoderms were also heavily affected, and the endocerid cephalopods died out completely, except for possible rare Silurian forms. The Ordovician-Silurian Extinction Events may have been caused by an ice age that occurred at the end of the Ordovician period as the end of the Late Ordovician was one of the coldest times in the last 600 million years of earth history.

References

External links

• Middle & Late Ordovician Climate
• The World during the Middle and Late Ordovician Archived 2005-03-21 at the Wayback Machine
• The Late Ordovician
• GeoWhen Database - Late Ordovician
• The Ordovician Mass Extinction Archived 2005-07-17 at the Wayback Machine
• BBC Evolution Weekend: Extinction Files