Birds are amazing animals. One kind of birds may look very different from another. But there's one thing all birds have in common: they all have feathers which help them fly, stay warm, and have beautiful colours. Most birds can fly, and some are excellent swimmers. Penguins, for example, cannot fly but they use their wings to swim fast. Where did birds come from? Scientists believe that millions of years ago some small, feathered dinosaurs that walked on two legs and could not fly turned into birds. It is easier to imagine a crocodile to be a dinosaur's relative, which is also true. But if you look closer at some big birds' legs, you can see that they look like dinosaurs' legs. And, of course, birds, dinosaurs and crocodiles all lay eggs. This is because they are related.