Direction: Dinosaurs developed in many different ways, but none of them ever developed a good brain. One of the reasons dinosaurs disappeared may be that they were not intelligent enough to know how to survive and escape from all their natural enemies. But some scientists believe that changes in the earth and in climate killed off the dinosaurs. Swamps dried up and mountains appeared, making life became difficult for dinosaurs that could not live on dry land . Also, changes in climate produced changes in vegetation, and since many dinosaurs were plant eaters, their food supply disappeared. Finally, as the earth began to have seasons, shifting from hot summers to snowy winters, dinosaurs could not fit themselves to these changes and gradually became extinct. There are other scientists who believe that the dinosaurs disappeared because of an incident that happened 65 million years ago. An enormous and very heavy asteroid hit the earth. There was a huge explosion and this caused tons of dust to be blasted into the earth's atmosphere. There was such a thick layer of dust covering our earth that it blocked out sunlight for as five years. That was how plants died and the dinosaurs were deprived of food. Eventually they starved to death.