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New Species:
Shellfish, trilobites, horseshoe crabs, mollusks, earliest primitive fish
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Mild climate |
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Land masses break into smaller continents |
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Sponges, algae; no land plant life |
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Many marine invertebrates; arthropods thrived |
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None |
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The Cambrian Period is the time when most of the major groups of animals first appear in the fossil record. Sometimes called the "Cambrian Explosion", this period is the time when the rate of evolution occured very quickly. A large number of species develop rapidly and we see the first animals with "hard parts." Among these is the trilobite, which is the closest ancestor to the horseshoe crab.
At the end of the Cambrain, there is a mass extinction of 50% of all animal families, including the trilobites, which is believed to be caused by glaciation. |
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