Thank dead dinosaurs if you like to sleep at night

Mammals were largely creatures of the night until the dinosaurs were killed off by an asteroid some 66 million years ago, a new study finds.

The findings, described in the journal Nature Ecology & Evolution, illuminate a pivotal transition in the history of Earth's living things.

Scientists have long wondered whether ancient mammals may have been primarily nocturnal because dinosaurs dominated daytime activities - an idea known as the "nocturnal bottleneck hypothesis".