They are warm-blooded that is, the temperature inside their bodies stay the same, more or less, even when it is quite warm or very cold outside. Another thing that sets mammals apart from other animals is their mammary glands, which produce milk. All young mammals feed on their mothers' milk until they can find and eat food by themselves. All mammals have four limbs. All mammals breath air.
All mammals are warm-blooded.
All mammals produce milk for their young. All mammals have hair even elephants and whales. Mammals have been around for 200 million years. There are about 4,000 different species of mammals alive today. The two most diverse groups of mammals are rodents and bats.