From bats that fly through dark skies, to skunks that release their noxious spray under moonlight, and even lions, tigers and leopards that prowl the night, a nocturnal existence is a way of life for a number of different animals all over the world.
This love of nightlife seems to have started much earlier than researchers previously believed in the lineage that led to mammals, maybe 300 million years ago, way before the first mammals dodged dinosaur feet 100 million years later, according to Reuters.
Researchers said on Sept. 3 in a study of fossils of small ring-shaped bones embedded in the eyes of an important group of ancient mammal relatives synapsids showed that many of them flourished at night or in the twilight.
The findings appear in the journal Proceedings of the Royal Society B this week.
The mammal relatives ascended around 320 million years ago and became the dominant land creatures during the Permian Period, which preceded the rise of the dinosaurs in the Triassic Period.
Plant and meat-eating beasts prospered worldwide.
"The study does give us new insights into the daily lives of some of our most ancient relatives," said Kenneth Angielczyk, a paleontologist with the Field Museum of Natural History in Chicago, according to Reuters.
The new findings contradicts conventional wisdom that the nocturnal lifestyle emerged with the appearance of the first bona fide mammals 200 million years ago since they needed to slink around in the dark to avoid being eaten by dinosaurs.
Researchers studied bones called scleral ossicles, which revealed the eye's dimensions and enable predictions about light sensitivity. This showed whether an animal was nocturnal or active during the day or active in twilight conditions.
Modern mammals lack these bones, according to Reuters.
Researchers examined museum collections from all over the world and found 38 specimens comprising 24 species, mainly from places like the United States, South Africa, Russia and Brazil.
"Specimens with well-preserved scleral rings are rare, so it took a lot of searching," Angielczyk said.
The eyes of ancient synapsids most likely spanned a range of light sensitivities, some suited to nighttime and others favoring daylight. The oldest synapsids possessed eye dimensions suited to night activity.
"Nocturnality comes with advantages and disadvantages," said another of the researchers, Lars Schmitz, a biology professor at Claremont McKenna, Pitzer and Scripps Colleges in California, according to Reuters.
"It's cooler at night, which may be beneficial for some species. As a hunter, it may be easier to approach prey. On the other hand, the dim light levels make it difficult for animals. Keen senses are beneficial," Schmitz added.
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