While the exact timeline is still being refined by paleontologists, the fossil record clearly shows that whales evolved from four-legged land mammals, likely resembling a small hippopotamus or a wolf. This transition happened gradually over millions of years, with creatures like *Indohyus* and *Pakicetus* representing intermediate stages.
Here's a simplified timeline:
* 50 million years ago: The first whale ancestors, like *Indohyus*, were small, semi-aquatic mammals living near water.
* 49 million years ago: *Pakicetus* evolved, featuring more aquatic adaptations.
* 40-34 million years ago: Whales evolved into fully aquatic forms, like *Dorudon*.
* 34 million years ago: Modern whale lineages began to diversify.
It's important to remember that this is a continuous process, and the transition from land to sea took millions of years. The ancestors of whales didn't suddenly jump into the ocean! They gradually adapted to a more aquatic lifestyle, evolving features like flippers, a streamlined body, and the ability to hold their breath for longer periods.