Reading 4

There are two different kinds of animals. First, there are animals without backbones. These were the first animals. These are animals like starfish, bugs, and crabs. Other animals have backbones. There are many different animals with backbones. Fish were the first animals with backbones. Fish live in the water. They cannot take in air like humans. They have to take in water to breathe. There are many different kinds of fish. Some fish live in the sea, and some live in lakes and rivers. Some fish, like sharks, are very large, but other fish are tiny. A very unusual kind of fish are eels. Eels look like snakes, but they are fish. For a long time, fish were the only animals. Then, some fish became able to get out of the water and move on land. These fish became "amphibians," which means "having two lives." One life is in the water, and the other life is on the land. A young amphibian lives in water. A fully grown amphibian lives on land and can take in air. The best known amphibian is the frog. At first, amphibians had their babies in water. Eventually, some amphibians became able to have their babies on land. The first animals to have their babies out of water were reptiles. Reptiles are animals like lizards, snakes, and crocodiles. Dinosaurs were reptiles, too. Dinosaurs were very large lizards that lived on the Earth millions of years ago. They have all disappeared around 65 million years ago. Some reptiles became very light and developed feathers. These became birds. Birds are light and can fly. Some birds swim or run instead of flying. The next animals to come along were mammals. Mammals have hair and produce milk for their young. Mammals are animals like dogs, cats, horses, and humans.