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The time period between 542- 488 million years ago marks the Cambrian period. The term Cambrian is derived from 'Cambria", a Roman word that means wales. This was the period when many kinds of invertebrates and the first vertebrates like fishes got discovered in the form of fossils.

The Silurian period: The Silurian period was the time between 443- 419 million years ago. The evolution and diversification of fishes are considered to happen during the Silurian period. The first form of freshwater fish is considered to be developed in that period.

The Ediacaran period: The time between 635-541 million years ago is the Ediacaran period. This period records diverse multicellular and microscopic organisms.

The Devonian period: The time between 419-358 was recorded as the Devonian period. It is considered that the first form of tetrapods and vertebrates appeared during this period. Major sea level changes and climate changes took place during the Devonian period.