Researchers recently found evidence that prehistoric mammals were nocturnal hunters by nature.

They've also uncovered proof this habit began about 300 million years ago.

Researchers discovered fossils of a group of extinct mammals called synapsids that had small ring-shaped bones called scleral ossicles. These bones indicate if an animal was active during the day or night and enable predictions about the light sensitivity of these mammals.

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The current bone structure of mammals lacks these bones.

Researchers searched through the world's museums to find these rare eye bones. They only found 38 specimens comprising 24 species.

One such species of mammal with the scleral ossicles bone was the extinct Dimetrodon. The animal is 11 feet long, four legged predator that has a back topped by a semicircular sail. The Dimetrodon hunted at night.         

Lars Schmitz, a biology professor from Claremont McKenna College and a member of the researcher team, said hunting at night has its benefits and drawbacks.

The fact that it's cooler at night may be a benefit for several species. While it makes it easier to approach prey, the darkness may also deter hunters from catching their prey. Therefore, keen senses are important to both the hunters and the hunted.

Since the fossils indicated activity 300 million years ago, it proves that mammal's "nightlife" didn't come from people hunting at night to avoid facing the wrath of dinosaurs.

This is because dinosaurs existed about 100 million years ago.

It seems there's a deeper cause for the night life of mammals.

The study was recently published in the journal, Proceedings of Royal Society B.

Tagssynapsids, scleral ossicles, ancient mammals, nocturnal, night life