Middle Ordovician
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The Middle Ordovician is the second subdivision of the Ordovician period. During this time warm shallow sea covered much of the land, and was home to a rich diversity of marine life.
North America straddled the equator, while the south-polar supercontinent of Gondwana included not only South America, Africa, India, Antarctica and Australia, but Southern Europe as well.
The trilobite-dominated Early Ordovician communities are replaced by generally more mixed ecosystems, in which brachiopods, bryozoa, molluscs and echinoderms all flourish, tabulate corals diversify and the first rugose corals appear; trilobites are no longer typically predominant. The planktonic graptolites remain diverse, with the Diplograptina making their appareance.
The earliest known armoured agnathan ("ostracoderm") vertebrate, Arandaspis, dates from the Middle Ordovician of Australia.
[edit] External links
- The World during the Middle and Late Ordovician paleogeography
- The Middle Ordovician
- GeoWhen Database - Middle Ordovician
| Ordovician period | ||
|---|---|---|
| Lower/Early Ordovician | Middle Ordovician | Upper/Late Ordovician |
| Tremadocian | Stage 2 | Stage 3 | Darriwilian | Stage 5 | Stage 6 Hirnantian |
