The first known whales lived roughly 50 million years ago, during the Eocene period.
They were four-legged, tiny mammals who lived in swamps and estuaries.
These early whales evolved more and more adopted to an aquatic lifestyle over time.
Their limbs shrank and became more streamlined, their tails grew larger and more powerful, and their bodies shrank.
Over the course of 40 million years, whales evolved a blowhole and echolocation.
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