Whales evolved from four-legged, even-toed, hoofed (ungulate) ancestors that lived on land about 50 million years ago. The first whales evolved over 50 million years ago, and the ancestors of both whales and hippos were terrestrial. The evolution of whales from land mammals to aquatic creatures took millions of years and involved many adaptations to facilitate life in the water. Some of the key adaptations include:
- Nostrils evolving into blowholes and moving to the top of the head
- Hind limbs disappearing and front limbs transforming into fins
- The body losing its fur and nearly all of its hair
- The tail becoming a horizontal, powerful propeller attached to the vertebral column
Whales closest living relatives are hippos, but they are not the ancestors of whales. Instead, whales evolved from a group of anthracotheres about 15 million years ago. Fossils of ancient whales called Basilosaurus show the link or intermediate between whales and their terrestrial ungulate ancestors. Gradually, whales tails became bigger and stronger for powerful swimming, and their back legs shrunk. Eventually, their nostrils moved to the top of their heads so that they could breathe easily.
