What are mammals?

Mammals are vertebrates that nourish young with milk and have hair at some point in life.

Diversity and reproduction

Most give birth to live young, but monotremes such as the platypus lay eggs. Marsupials and placental mammals follow different developmental paths. Runners on land, tree dwellers, flying bats and aquatic whales all belong to the group. Temperature regulation, lung breathing and parental care are important in many species, but diet, social life and care vary. Whales are mammals, not fish.

Habitats and ecological relationships

Herbivorous mammals affect vegetation, predators interact with prey populations and some species disperse seeds. The diversity of rodents and bats matters alongside large mammals. Habitat loss, hunting and conflict with people do not affect every species equally. Each species’ life history and local pressures require separate study.