Millions of years ago there were many types of dinosaurs on earth. Most dinosaurs were plant�eaters. The Apatosaurus, for example, had a long thin neck so that it could eat leaves from trees. Other dinosaurs were meat�eaters. The Tyrannosaurus Rex killed smaller dinosaurs for food.
Dinosaurs were real animals that once lived on the earth, but they died out about 65 million years ago. The disappearance of the dinosaurs is in some way a great mystery (谜).① Some scientists think that the climate (气候) changed suddenly. Fossils (化石) of trees tell us that the temperature dropped a lot and that the level of the sea dropped as well. ② This means that it got suddenly much colder. Perhaps the dinosaurs were too slow to change with the climate.
A new idea is that a meteor (流星) crashed into the earth. Scientists discovered a place in Mexico where they think the meteor crashed. They think that there was a lot of dust from the meteor. The dust landed on the plants. Also the dust blocked (阻挡) the sun's light for as long as five years. Many animals, including dinosaurs, were plant�eaters, and perhaps the dust killed them. This means there was nothing left for meat�eating dinosaurs to eat, and so they died out. But, as many animals from that time didn�t die, we are not 100% sure what really happened.
Animals are natural resources that people have wasted all through our history.
Animals have been killed for their fur and feathers, for food, for sport, and simply because they were in the way. Thousands of kinds of animals have disappeared from the world forever. Hundreds more are on the danger list today. About 170 kinds in the United States alone are considered in danger.①
Why should people care? Because we need animals. And because once they are gone, there will never be any more.
Animals are more than just beautiful and interesting.② They are more than just a source of food. Every animal has its place in the balance of nature (生态平衡). Destroying one kind of animal can create many problems.
For example, when farmers killed large numbers of hawks (老鹰), the farmers� stores of corn and grain were destroyed by rats and mice. Why? Because hawks eat rats and mice. With no hawks to keep down their numbers, the rats and mice multiplied(繁殖)quickly.
Luckily, some people are working to help save the animals. Some groups raise money to let people know about the problem. And they try to get the governments to pass laws protecting animals in danger.
Quite a few countries have passed laws. These laws forbid (禁止) the killing of any animals or plants on the danger list. Slowly, the number of some animals in danger is growing.