BEACON TRANSCRIPT – The fact that most mammals are diurnal comes as no surprise to us nowadays, but it’s hasn’t always been like that. Researchers tracked down the origin of this lifestyle among the creatures, and discovered it dates back to soon after dinosaurs went extinct. Before that, they seemed to have been leading mostly nocturnal lifestyles.
Mammals became diurnal soon after dinosaurs had disappeared
There was quite a long period of time when mammals and dinosaurs coexisted. However, back then, the former were a bit different. Studies show they were a lot smaller and active mostly during nighttime, probably as an attempt to avoid becoming the prey of the huge reptiles.
Therefore, it’s not unusual to say mammals became diurnal when dinosaur went extinct. Since the imminent threat posed by the reptiles was gone, they found it easier to go out in the daylight to graze and move around.
To make sure the correlation is liable, researchers used a series of methods to test their hypothesis. All of them returned the same result. They collected data from a number of 2,415 species which still exist today, and ran some simulations which revealed the evolution of their behavior over millions of years.
It’s not clear if the extinction of the reptiles caused this change in mammals
They selected two different family trees, so that they might account for possible differences. However, both analyses revealed the mammals turned diurnal not long after dinosaurs went extinct. The process was gradual, as the creatures first engaged in activities which could be undertaken both at night and during the day.
Also, the discoveries reveal our direct ancestors, namely those mammals who later evolved into simian primates, were the first to switch from being nocturnal to being diurnal. This can account for the significantly better vision these primates have today, compared to other mammals. However, the study couldn’t confirm that the disappearance of dinosaurs was the clear cause of this shift in their behavior.