The Cretaceous-Paleogene extinction event occurred 65 million years ago.  In this extinction 17% of families, 50% of all genera, and 75% of all species became extinct.  This extinction is believed to have been caused by an asteroid impact at the Chicxulub crater in the Yucatan plateau.  Before this extinction, mammals were few and small, most resembling field mice.  This extinction may have given rise to the reign of mammals.

Cretaceous–Paleogene extinction event – Wikipedia en.wikipedia.org The Cretaceous–Paleogene (K–Pg) extinction event, also known as the Cretaceous–Tertiary (K–T) extinction, was a mass extinction of some three-quarters of the …

BBC Nature – Cretaceous-Tertiary mass extinction videos … http://www.bbc.co.uk Cretaceous-Tertiary mass extinction. The Cretaceous-Tertiary mass extinction – also known as the K/T extinction – is famed for the death of the dinosaurs.

Dinosaur Extinction, Cretaceous-Tertiary Extinction … science.nationalgeographic.com Learn about the dinosaur extinction (the Cretaceous-Tertiary extinction) and get information, facts, and more about dinosaur extinctions from National Geographic.