Picture a dinosaur. Huge, menacing creatures, they ruled the Earth for nearly 200 million years, striking fear with every ground-shaking stride. Yet these great beasts were no match for a 6-mile wide meteor that struck near modern-day Mexico 65 million years ago, incinerating everything in its path. This catastrophic impact — called the Cretaceous-Tertiary or K/T extinction event — spelled doom for the dinosaurs and many other species. Some animals, however, including many small mammals, managed to survive.