The age of mammals

Sixty-six million years ago an asteroid struck what is now Mexico, and about three quarters of all species died out, including every dinosaur except the birds. Mammals had lived alongside the dinosaurs for more than 150 million years. With the dinosaurs gone, the last 66 million years became the age of mammals. Some of the strangest are the whales.

Whales that walked

Whales and dolphins are mammals: they breathe air, are warm-blooded and feed their young on milk. Their ancestors lived on land. About 50 million years ago lived Pakicetus, a goat-sized animal with four legs that lived in or near estuaries. It looked nothing like a whale, but scientists recognise it as one of the first cetaceans.

The change that followed was fast. Within 10 million years, from Pakicetus to Dorudon, cetaceans had completely adapted to life in the water. About 34 million years ago one group began to feed by filtering small animals from the sea. These were the first baleen whales, the group that includes the humpback and the blue whale.

The largest animal ever

The blue whale is alive today, and it is the largest animal ever to have lived on our planet. It can be up to about 110 feet, or 33.5 metres, long. Here it is to scale, beside a person.

Mammoths

Through the ice ages, Woolly mammoths roamed the northern hemisphere for at least half a million years. They were still common 20,000 years ago, but within 10,000 years they were down to small groups on islands off Siberia and Alaska. The last of them died about 4,000 years ago.

By then our own species, which evolved in Africa about 300,000 years ago, had spread across the world. Read about our own story in Before us.