The first mammals developed were from reptiles about 180 million years ago. In the past 65 million years many mammals have become vertebrates. Some mammals migrate, other mammals hibernate when the weather is cool. Most mammals shed their hair during the warm weather. When it is cold weather the animals will grow a new coat.
All mammals are warm blooded and have a great sense of smell.
Mammals talk to each other by making sounds. They also have a big brains and remember very well. Mammals are classified in three groups. The groups are placental mammals, pouched mammals, and monotrems. A mammals birth period depends on how big the animal is.