Dinosaurs(恐龙)once lived on the earth for a long time. They suddenly disappeared millions of years ago. What happened to them? That's still a mystery. People never stop searching for the answer.
Some US scientists say it is because there were not enough male(雄性的)dinosaurs. They got this idea after researching crocodiles(鳄鱼).
Mother crocodiles lay eggs and later baby crocodiles come out. The local temperature decides the sex(性别)of the baby crocodile. When the eggs are at a temperature of 26℃ to 30℃,the babies are all girls; when the temperature is 30℃ to 34℃,there are both boys and girls; when it is 34℃ to 36℃, only boys are born.
Dinosaurs' babies also came from eggs. So scientists have given us a new picture: millions of years ago, it suddenly became very cold. Almost all dinosaur babies were girls. There were fewer and fewer male dinosaurs. Mother dinosaurs could not give birth to more babies. Finally, these powerful animals disappeared.
