Over millions of years, these animals adapted to an aquatic lifestyle. Their hind limbs gradually reduced in size, their bodies became streamlined, and their nostrils migrated to the top of their heads.
Here's a simplified timeline of whale evolution:
* 50 million years ago: Indohyus, a small, deer-like mammal with hooves, lives in shallow water.
* 49 million years ago: Pakicetus, a slightly larger animal with larger teeth, is still mostly land-based but spends more time in water.
* 40 million years ago: Ambulocetus, a creature with powerful hind limbs and a tail adapted for swimming, spends most of its life in water.
* 37 million years ago: Rodhocetus, a streamlined animal with reduced hind limbs, is fully aquatic.
* 34 million years ago: Dorudon, a whale with a dolphin-like shape, is fully adapted to life in the ocean.
Key Features of Whale Evolution:
* Nostrils migrating to the top of the head: This allowed them to breathe while staying submerged.
* Hind limbs becoming smaller: Their hind limbs gradually reduced in size and eventually disappeared, becoming vestigial structures.
* Developing a streamlined body: Their bodies became more streamlined, allowing them to swim more efficiently.
* Developing a powerful tail for propulsion: Their tails evolved to be powerful for swimming.
* Developing echolocation: Some whales, like dolphins, developed echolocation to navigate and hunt in murky waters.
Today, whales are incredibly diverse and include both toothed whales (like dolphins and porpoises) and baleen whales (like humpback and blue whales).