The Cretaceous period is an interval of geologic time that occurred 144-165 million years ago, in the Mesozoic Era.

In the seas, marine invertebrates flourished and bone fishes evolved. There were several different marine invertebrates and bony fish in the water. On land, many different flowering plants arose, and insects, bees in particular, began their thriving partnership with them. Mammals and birds remained inconspicuous, while the reptiles continued their dominance. The many dinosaurs reached the peak of their evolution during this period but suddenly became extinct at its end. No one knows exactly why the dinosaurs became extinct, but it was around the end of the Cretaceous period that they disappeared.

So, in general terms, the Cretaceous period is a time when many of the insects, marine life and mammals made huge advances in evolution. The Cretaceous period is the era which contains the youngest dinosaur bones.