- Late Ordovician
The Late Ordovician, also called the Upper Ordovician by
geologist s, is the third epoch of theOrdovician period.At this time Western and
Central Europe andNorth America collided to formLaurentia , while glaciers built up inGondwana , which was positioned over theSouth 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
plankton ic forms likeconodont s,graptolite s, and some groups oftrilobite s (Agnostida andPytchopariida , which completely died out, and theAsaphida which were much reduced).Brachiopod s,bryozoa ns andechinoderm s were also heavily affected, and theendocerid cephalopod s died out completely, except for possible rareSilurian 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.External links
* [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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