Scientists Say: Mammal

Mammal (noun, “MAM-mal”)

Mammals are a diverse group of animals. They include about 6,600 known, living species. Many of them, including humans, cats and dogs, live on land. Others, such as dolphins and whales, live underwater. And some — bats — even fly.

Mammals tend to share a few distinguishing traits. All are vertebrates. That means they have a backbone. Almost all have fur or hair, even if it is just a tiny bit. Most mammals give birth to live young. And mother mammals produce milk to feed their babies.

Some exceptions to t...