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How did whales end up living in the ocean?

Have you ever wondered how whales - who are air-breathing mammals - ended up living in the ocean? Their evolution journey from land to sea is remarkable. We know whales are superbly adapted for underwater life….but where did they come from?

Modern whales are most closely related to hoofed mammals from a group called ungulates. This group includes giraffes, camels, deer, and hippos (the whales’ closest living relative).

Looking at a whale’s body and biology, there are plenty of clues to show that their ancestors were land mammals. For example, whales, like all mammals nurse their babies with their own milk. More clues are found in the whale’s skeleton – inside their front flippers they have arm, hand, and finger bones, and they still have hip bones which are left from a time when their ancestors had back legs.

Using the fossil record, we can track the whale’s evolution journey as they transformed into marine specialists. Scientists can recognise extinct whales from their unique earbones and skulls. There was a series of transitional whales who were amphibious (they could walk and swim) before the fully marine whales appeared.

Transitional whales had features of both land and marine mammals. Over time their front legs became flippers, their back legs shrunk, their tails became powerful for swimming, their nostrils became blowholes, and their eyes moved to the sides of their heads so they could see prey under the water.

Meet the Extinct Transitional whales…

Ilustrations by Elly Walton

40 million years ago

Basilosaurus illustration
was mistaken for a giant marine dinosaur at first and given a dinosaur name. Basilosaurus is the first prehistoric whale to live entirely at sea. They had serpent-like bodies, powerful tails with small flukes, blowholes, front flippers, teeny back legs, and ear bones just like modern whales.

40 million years ago

Durodon illustration
was a smaller whale living in the ocean at the same time as Basilosaurus. They ate fish and swam just like a dolphin. Dorudon descendants went on to evolve into modern whales and dolphins34 million years ago.

47 million years ago

Rodhocetus illustration
was an otter-like prehistoric whale that had a flexible spine and is the earliest known mammal to swim using the tail for propulsion. Their nostrils were further back along the snout, becoming more like blowholes.

48 million years ago

Ambulocetus illustration
Ambulocetus means the ‘walking whale’. They behaved like crocodiles do today - they could walk on their short legs and swam powered by their big, paddle-like feet. They had teeth and ear bones similar to modern whales.

49 million years ago

Pakicetus illustration
Pakicetus looked more like a wolf than a whale! They used their legs to swim and had pointy teeth for eating fish. Their eyes were on top of their head allowing them to see above water when submerged.


50 million years ago

Ambulocetus illustration
Indohyus is the oldest known whale ancestor. These small, deer-like mammals lived on land. Their skulls and earbones were whale-like. Indohyus had thick, heavy leg bones which helped weigh them down and enabled them to walk along the riverbed, hiding from predators.


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