After birth the young were looked after by their mothers, who fed them a rich food called milk. Mammals were the only animals able to make this wonderful food. Then began a long period of care and training when the young learnt from their parents.
Unlike dinosaurs, who probably needed the Sun's heat to keep them warm, the mammals had fur to keep them warm. They also had a better blood system.

Mammals were also far more intelligent than dinosaurs. Even the stupidest mammal is a genius compared to the brightest reptile. Their long development, when they are cared for by their mother, is what lets mammals' brains grow so much more than reptiles'.
Mammals first appeared about 200 million years ago. It is strange that while the mammals had better bodies and brains than the dinosaurs, even so for a long time they were unable to spread. This was probably because most life-styles were already taken by the less advanced but more common dinosaurs. Mammals stayed as small shrew-like insect-eating animals, perhaps only coming out at night.

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