- Late Ordovician
The Late Ordovician, also called the Upper Ordovician by
geologists, is the third epoch of the Ordovicianperiod.
At this time Western and
Central Europeand North Americacollided 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.
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 ( Agnostidaand Pytchopariida, which completely died out, and the Asaphidawhich were much reduced). Brachiopods, bryozoans and echinoderms were also heavily affected, and the endocerid cephalopods died out completely, except for possible rare Silurianforms. 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.
* [http://www.scotese.com/mlordcli.htm Middle & Late Ordovician Climate]
* [http://zircon.geology.union.edu/Gildner/globe.html The World during the Middle and Late Ordovician] paleogeography
* [http://www.palaeos.com/Paleozoic/Ordovician/LateOrd.html The Late Ordovician]
* [http://www.stratigraphy.org/geowhen/stages/Late_Ordovician.html GeoWhen Database - Late Ordovician]
* [http://hannover.park.org/Canada/Museum/extinction/ordmass.html The Ordovician Mass Extinction]
* [http://www.bbc.co.uk/education/darwin/exfiles/ordovician.htm BBC Evolution Weekend: Extinction Files] (very brief entry)
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