The diversity of life on earth is truly astounding; over 2 billion species have been identified. With all this diversity humans have come up with ways of organizing, or classifying all the biological diversity. An animal “class” is made up of animals that are all alike in important ways. Classes of organisms make it easier to study related animals. There are five important classes represented at the Denver Zoo: mammals, birds, fish, reptiles, amphibians, and one larger group, the invertebrates.
MAMMALS: Mammals are warm-blooded (endothermic) animals with a backbone (vertebrates) which share the characteristics of having hair or fur and mammary glands that produce milk to nourish their young. The astonishing diversity among mammals ranges from tiny field mice the size of a thimble to the massive blue whale. Mammals occupy all continents and can live on land, below ground, in trees, in the air and in fresh or salt water. Humans are members of the mammal family.
