Mammals are viviparous animals that breathe with lungs and have hair or fur. They can be carnivores, herbivores, or omnivores. Baby mammals drink milk from their mothers. Most mammals have four legs but some use flippers to move in water. Birds are oviparous animals that incubate eggs and have feathers. They find food for their babies until they can feed themselves. Birds breathe with lungs and have beaks adapted for their diets.