When did the Chalky Cretaceous Start?

The Cretaceous Period was very important in the story of the dinosaurs. It began 145 million years ago. Its  name derives from the Latin creta meaning chalk. It is often abbreviated to K. It is the final chapter in the so-called Mesozoic ("Middle Life") Era, the era of the dinosaurs. Birds, crocodiles and the coelacanth are the closest living relatives of the dinosaurs.