Birds = These are one of only two types of vertebrates that are warm-blooded. Their bodies are covered with feathers. These animals bodies are streamlined and light for flight. Their bones are hollow and have light weight to also help them fly. They lay hard eggs in nests.
Mammals = These vertabrates probably developed from flesh eating reptiles. They are the most complex of modern animals. All mammals are warm blooded and provide milk for their young. They care for their young until they can survive on their own. One type of mammal, the monotremes, lay eggs. All others have young form inside the mother.
