There are a number of different theories as to why the dinosaurs became extinct. Most scientists favour the theory that states that a giant comet slammed into the Gulf of Mexico, causing global climatic and environmental chaos. The sun was blocked out for years, half of all the plants on earth set on fire. Virtually every animal over 10kg went extinct, including the dinosaurs, pterosaurs and marine reptiles. The only dinosaurs that survived were the tiny feathered variety we know as birds. Also among the survivors were tiny mammals, among them our very own ancestors.