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150
15mya - Cetotherium
Cetotherium was the first Baleen whale; it ate plankton, and was the final step in the evolution of the whale before modern whales. It was not as aggressive as its ancestors, and was probably preyed upon by sharks and other hostile animals. -
Period: 150 to 500
15 to 50 million years ago
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450
45mya - Protocetus
These animals developed even more to the sea, and began to spread to different parts of the world, though still in shallow waters. Despite this, they still could walk on land to a certain degree, and there is evidence that they gave birth on land. -
500
50mya - Pakicetus
Pakicetus lived in the early Eocene. They drank fresh water, and lived near streams and floodplains in an arid environment. They ate small mammals and freshwater fish. -
49mya - Ambulocetus
Ambulocetus was amphibious, and looked similar to a crocodile. It could live in a wider range of water environments. It was shorter, longer, and bigger than it's ancestor, and wasn't necessarily fast, but could both swim and walk. -
48mya - Kutchicetus
Kutchicetus was the result of the earlier whale ancestors adapting more and more to water, namely salt water. They did not ingest freshwater and seemed to have lived in shallow lagoons and near-shore ocean areas. Due to weak eyesight, it depended on its other senses, and was a decent swimmer. -
38mya - Basilosaurus
Being the first amphibious ancestor of the whale, the Basilosaurus was a very long, full-fledged whale that had excellent hearing, a blowhole-like nose, and a small brain, which made it relatively solitary. It lacked echolocation, and fed on fish.
