noun
Cretaceous period
Geological period from about 145 to 66 million years ago, following the Jurassic and preceding the Paleogene.
白亜紀は恐竜が繁栄した最後の時代です。
The Cretaceous period was the last era in which dinosaurs flourished.
The Paleogene period, which followed the Cretaceous.
From 白亜 (はくあ, 'white chalk') + 紀 (き, 'geological period'), referring to the extensive chalk deposits from this era.