Which of the following animals is a mammal: Human, Dog, Elephants, Cat, Bats, Goat, Bears, Sheep, Wolf, Lion, Squirrel, Koala, Cheetah, Deer, Orca, Gorillas, Camel, Hamsters, Hedgehog, Blue whale, Chimpanzee

All of them are mammals! They have very distinct characteristics and live in different environments. However, it's characteristic of mammals that they have three middle ear bones, milk-producing mammary glands, neocortex brain regions, and fur or hair.