The extinction of dinosaurs, and many other species, occurred about 66 million years ago at the end of the Cretaceous period. The dominant theory for this extinction is the Chicxulub asteroid impact theory, which suggests that an asteroid or comet about 10–15 kilometres (6–9 miles) in diameter struck what is now the Yucatán Peninsula in Mexico. This impact would have caused a massive crater, tsunamis, and wildfires, as well as blocking sunlight and causing a global winter.

Other theories for the dinosaurs' extinction include changes in climate, volcanic eruptions, and disease. However, the asteroid impact theory is the most widely accepted explanation.

Some small species of dinosaurs, such as the ancestors of birds, survived the extinction event and eventually evolved into the modern birds we see today. Other survivors included turtles, crocodiles, lizards, and snakes, as well as mammals such as opossums, bats, and rodents.