Mammals (Class Mammalia)

There have been mammals living on this planet for 200 million years.  The greatest diversity or different kinds of mammal species (kinds) existed about 15 million years ago.  Today, there are about 4,000 different species of mammals.  Nearly half of all these species are rodents.

The largest animals alive, such as the elephant and whales are mammals.  In fact, the blue whale is the largest animal ever to have lived on earth.  There also are very small mammals—shrews are only one example.

All mammals are vertebrate animals, which means they have a backbone.  Mammals are the only animals that have hair.  All mammals breathe air, even whales and dolphins.  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.

Fast Facts: 

• All mammals have a backbone.

• 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.

  Mammal Diversity

Mammals are divided up into groups of related animals, called Orders.  Below you'll find the name of the most common orders and some examples.