50 – 60 million years ago

The age of the mammals

Brontotherium

Mammals are warm-blooded creatures that suckle their young. Babies are almost always born live, although a few still lay eggs like the reptiles from which they evolved: the duckbill platypus and two species of spiny anteater.

Although the first mammals evolved at about the same time as the dinosaurs, it was not until about seven months ago in Earth's life (about 50 – 60 million years ago in real time) that huge numbers of different kinds of mammal, and of all shapes and sizes, began to evolve.

There were carnivores, insectivores and herbivores. Some remained small, but others, for example Brontotherium, were as big as some of the large dinosaurs.

Some developed wings and took to the air: the bats. Some even returned to the seas, lost the use of their limbs for walking and developed flippers for swimming: the whales and dolphins. There were also primates, which looked a bit like lemurs and from which monkeys, apes and humans were eventually to evolve.


The Earth is now 46 years oldBack to 100-0 million years ago

The Earth is now 46 years old.