The Silurian Period, 444 mya - 419 mya

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The Silurian Period is the shortest of the time periods in the paleozoic, being the third of the six major periods. It begins around 444 million years ago, as the glaciers of the ice age at the closing of the Ordovician receded, and ends around 419 million years ago, with some minor extinction events. For the most part, the Silurian Period was warm and wet.

While fungi and some very primitive plants were colonizing the land toward the end of the Ordovician, the Silurian Period was a time of significant colonization of land by both plants and animals. In terms of plants, the Silurian Period saw a continual development of mosses, liverworts, and lichens, which had all probably appeared by the late Ordovician, but also the development of new plants without leaves, such as Cooksonia (which was a sporophyte for some moss-like plant that had made steps toward become more fern-like or at least horsetail-like). Animals followed the plants on to land, and it is during the Silurian that we see a variety of arthropods (especially centipedes and millipedes) leaving traces in the fossil record. Eurypterids (sea scorpions) also probably came up on land during the Silurian. While fossil evidence is scant to nonexistent, it is probably a safe guess that some worms (perhaps nematodes and annelids) were on land as well, although there is not yet fossil evidence for this.

Some of the continents drifted closer together during the Silurian, but many were stuck together in Gondwana way down near the south pole for most of this period. Many continental shelfs were covered with shallow seas, creating a good environment for many sea creatures. Jawed fish and spiny sharks swam the seas, and by the end of the Silurian the oceans had bony fish. For most of the Silurian, the seas were full of eurypterids, and the shallow sea floors were covered with crinoids, brachiopods, corals, sponges, bryozoans, and graptolites.

 

Links about the Silurian Period:

1. The University of California has a fine short page on the Silurian Period.

2. The experts on the Silurian Period may be involved in the International Subcommission on Silurian Stratigraphy.

3. The Milwaukee Public Museum offers a tour of a virtual Silurian Reef.

4. National Geographic has a page on the Silurian Period.

5. Palaeos has a fantastic page about primitve plants and their early evolution.

6. John Merck shares his lecture notes about eurypterids and scorpions on land.

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