Here's the breakdown:
* Ancient ancestors: The ancestors of whales were small, four-legged, hoofed mammals that lived on land about 50 million years ago.
* Transition to water: Over millions of years, these animals adapted to life in water. Their legs became flippers, their bodies became streamlined, and their nostrils moved to the top of their heads.
* Fossil evidence: Scientists have discovered many fossils that trace this evolutionary path, showing the gradual changes that occurred as these animals adapted to aquatic life.
Key examples of transitional fossils:
* Indohyus: An early whale ancestor that was a small, land-dwelling mammal with hooves.
* Pakicetus: A semi-aquatic mammal that lived in shallow water and had a long snout and teeth adapted for catching fish.
* Ambulocetus: A larger, more aquatic mammal that spent most of its time in water and had webbed feet.
* Rodhocetus: An animal with reduced hind limbs and a tail fluke that allowed for swimming.
So, while whales may look very different from their land-dwelling ancestors, the fossil record clearly shows their evolutionary connection. This incredible transition from land to water is a testament to the power of natural selection and the incredible diversity of life on Earth.