Answer:
Fish, reptiles, amphibians, birds and mammals all have bones. Fish, reptiles and amphibians are cold-blooded animals. Scientists believe that fish were the first animals to develop bones. Some primitive fish, like sharks, have skeletons made out of a tough material called cartilage, but all the rest have bones. Fish take in oxygen from the water through gills.
Amphibians were the first animals to develop legs. Frogs, toads and salamanders are amphibians. When young, they live in the water and use gills to breathe. As adults, they develop legs and lungs, and live on land.
Reptiles are scaly animals, such as snakes, lizards, turtles and alligators. They're cold-blooded like fish and amphibians. Unlike amphibians, they have lungs and breathe oxygen from the air from the time they are hatched from their eggs. Reptiles have been around for a very, very long time -- about 300 million years! Dinosaurs were reptiles. But turtles were here before the dinosaurs and have outlasted them.
Birds are the only animals with feathers. They're warm-blooded. They have bills but no teeth. They hatch their young out of eggs. They have two legs and two wings, and most know how to fly. They have hollow bones that help keep their bodies light enough to take off into the air. Like you, birds have lungs and breathe oxygen. At this time of year, you might observe some species of birds migrating from their summer homes in the north to their winter homes in the south.
The animals we have most in common with are mammals. Like us, they're warm and fuzzy. That's because all 12,000 species of mammals -- including whales -- are warm-blooded and have hair in some form. Mammals all have backbones and lungs and bear live young. They have four appendages -- two arms and two legs, in the case of human beings.
Mammals have another important characteristic in common: When young, mammals are fed on milk produced by their mothers' bodies. Mammal babies -- especially humans -- depend on their parents for longer periods than other animals to teach them many of the skills needed to survive.
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