You Can Thank The Extinction Of The Dinosaurs For Our Daytime Existence
Our bouts of insomnia aren’t just a result of our hectic modern lifestyles — they may also be the product of mammals’ having to hide from dinosaurs tens of millions of years ago.
Mammals were largely creatures of the night, right up 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, also sheds light on a pivotal transition in the history of Earth's living things. Most notably: it gave rise to the dominant species of the planet — us, the diurnal, bipedal great apes.
Living mammal species today carry many signs of a literal dark past. For example, most mammals (except humans and many other primates) don't have a fovea, an area in the eye's retina that allows for the clearest vision. The shape of many mammals' eyes also favors low-light sensitivity rather than the ability to see sharply.
Furthermore, the researchers who conducted the study specifically focused on species who could be described under three main categories — nocturnal, diurnal, and cathemeral — and ran an analysis of the mammalian family tree. They found that the ancestors of today's mammals were probably nocturnal, and probably stayed nocturnal until around the time that the dinosaurs died off.
"On balance, our evidence suggests that mammals remained nocturnal throughout the Mesozoic," one author wrote in the study, referring to the era from about 252 million to 66 million years ago known informally as the Age of Reptiles.
Their analysis showed that the shift among some mammal species to diurnal activity happened after the extinction event, with the earliest mammals — those that were strictly diurnal included simian primates—began emerging from the shadows around 52 million to 33 million years ago. Though scientists can't say that one caused the other, the study provides fresh circumstantial evidence that supports such happenings.
But there's also mounting evidence that dinosaurs were in decline long before the asteroid wiped them out, leveraging more time for our mammalian ancestors to explore the world during the daytime, seizing the day’s bevy of nutritious food offerings.
Next time you find yourself up all night for no reason — feel free to blame T-rex and clan for that episode of insomnia.
(Feature image, courtesy of Wikimedia Commons)