Cretaceous

The Cretaceous is a geologic period and system, reaching from the end of the Jurassic Period, (145.5 ± 4 million years ago (Ma) to the beginning of the Paleocene Period, 65.5 ± 0.3 Ma. It is the youngest geological period of the Mesozoic, and at 80 million years long, the longest period of the Phanerozoic. The end of the Cretaceous defines the boundary between the Mesozoic and Cenozoic eras.

Cretaceous in "Hatching Season"
Paula Shaffer travelled back to the Cretaceous on a grant to do a field-study of hadrosaurs.