End-cretaceous

Towards the end of the Cretaceous diversity declined sharply and only a few widespread genera are found in the uppermost beds, these finally disappearing in the end-Cretaceous extinctions.

Although the end-Cretaceous bolide impact is contemporaneous with the abrupt end of the reign of dinosaurs, early mammals survived the catastrophic event […].

The end Cretaceous catastrophe that killed the dinosaurs 65 million years ago did for these animals too and the oceans were quieter for a while, but within fifteen million years or so the ancestors of dolphins and whales were exploiting the rich seas of the Eocene.