Mammals—a group that include humans—are warm-blooded animals with hair and vertebrates, or backbones. Unlike other classes of animals, female mammals produce milk to nourish their young. Almost all mammals give birth to live young (except for the platypus and echidna, which lay eggs).
Scientists have identified more than 5,400 mammal species on Earth, roughly one-fifth of which are known to be threatened or extinct. One of the most threatened order of mammals is the primate, which includes monkeys and apes. The United States has more than 400 mammal species. Of those mammals, nearly a quarter are listed on the U.S. endangered species list for reasons including habitat loss, climate change, pollution, and disease.
Bats
Nocturnal, flying mammals that eat fruits and insects
| Bats | Indiana Bat |
| Jamaican Fruit-Eating Bat | Little Brown Bat |
Rodents
Gnawing mammals with a single pair of incisors
| American Beaver | Black-Tailed Prairie Dog |
| Dusky-Footed Woodrat | Flying Squirrels |
| Pocket Gophers | Red Squirrel |
| Red Tree Vole |
Lagomorphs
Gnawing mammals with two pairs of incisors
| American Pika | Snowshoe Hare |
| Swamp Rabbit |
Moles and Armadillos
Burrowing mammals
| Moles | Nine-Banded Armadillo |
Carnivores
Meat-eating mammals, such as bears, felines, and canines
| Black Bear | Canada Lynx |
| Florida Panther | Gray Wolf |
| Grizzly Bear | Hawaiian Monk Seal |
| Mountain Lion | North American River Otter |
| Polar Bear | Raccoon |
| Red Fox | Red Wolf |
| Wolverine |
Ungulates
Hooved mammals with four legs
| American Bison | Bighorn Sheep |
| Key Deer | Moose |
| Mule Deer | Pronghorn |
Cetaceans and Sirenians
Aquatic mammals with paddle-shaped forelimbs
| Blue Whale | Harbor Porpoise |
| Humpback Whale | Orca |
| Sperm Whale | Spinner Dolphin |
| West Indian Manatee |
