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Such rocks contain traces that geoscientists use to mark the change from the Cretaceous period to the Palaeogene period in Earth’s history.

The tree with the shorter timeline suggested that mammals began to occupy a daytime niche after the reign of non-avian dinosaurs was ended by the Cretaceous/Palaeogene extinction, triggered when an asteroid struck the Yucatán penninsula in what is now Mexico, around 66 million years ago.

The Cretaceous/Palaeogene extinction “was the best thing that happened for mammals”, Kirk says.

In some books, too, you will find the tertiary and quaternary taken out and replaced by periods of different lengths called the Palaeogene and Neogene.

In addition, as observed for many other plant lineages, this orchid-specific WGD might be associated with the Cretaceous/Palaeogene boundary15.