1. Dinosaurs are a general term for a class of reptiles that appeared in Mesozoic. Strong limbs, a long tail and a huge body. They mainly inhabit the open areas of woodland or lakeshore plain.

2. There are many kinds of dinosaurs, and their shapes and habits are very different. The largest fragile double-chambered dragon may be more than 50 meters, while the smallest hummingbird may be less than 10 cm. As far as eating habits are concerned, there are docile herbivores and fierce carnivores, as well as omnivorous dinosaurs who are both vegetarian and vegetarian.

3. In Mesozoic, when dinosaurs lived, the content of carbon dioxide in the atmosphere was high, indicating that dinosaurs had strong adaptability. Mammals had appeared at that time, but they had been in a weak position and developed slowly in Mesozoic.

4. With the passage of time, by the end of Cretaceous, great changes had taken place in the atmospheric environment, with the decrease of carbon dioxide content and the increase of oxygen content, which was unfavorable to dinosaurs. In the new environment, it is easy to get sick, and the disease will spread like a plague.

5. The new atmospheric environment is more suitable for the survival of mammals, and mammals have become more advanced and adaptable competitors. Under the action of these two factors, dinosaurs finally became extinct.