Blackwell Publishing
Precambrian Paleozoic Mesozoic Cainozoic

Between 670-550 mya the first metazoa - multicellular animals - aquatic animals such as jellyfish and worms. This fossil Tribrachidium - a relative of modern jellyfish - may have swum freely or moved over the sea floor. It is not until the Cambrian period that the diversity and number of fossils increases.

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