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Fish were the first chordates (organisms with a spinal cord), and also the first vertebrates (organisms with a spinal column). Developing a spinal cord gave them an advantage over their arthropod enemies, because they could swim faster and were much more agile.

It is difficult to say exactly when the first fish evolved or which was the first fish, but we do know that the earliest fish evolved between 400-500 million years ago. They were jawless, with gills and scales but no fins. Eventually fish greatly diversified and occupied almost every water environment. They developed fins and a strong tail to help them swim better. They were also the first animals to develop jaws and teeth, enabling them to eat other animals.

The following lists the possible evolution of the fish over time:

About 460 to 480 million years ago: The first jawless fish evolve. (It's worth noting here that this starting point is hotly debated in the scientific community.)

About 450 million years ago: The first jawed fish emerges.

About 390 million years ago: The ancestors of the bony fish evolve.

About 380 million years ago: The first shark-like fish evolves.

About 360 million years ago: The early offshoots of the bony fish (Osteichthyes) evolve into the first amphibians (intermediates between fish and reptiles).

About 175 million years ago: The first true bony fish emerge.

Between 190 and 135 million years ago: The first modern sharks evolve.

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14y ago

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