Why death of dinosaurs helped mammals thrive
BRITAIN: With enormous predators such as Tyrannosaurus Rex marching around in the daytime it is not surprising that the first mammals chose to live under the cover of darkness.
In fact a study from University College London (UCL) and Tel Aviv University has found that our ancestors did not emerge from the shadows until after the dinosaurs became extinct, around
66 million years ago.
Before then, all mammals were nocturnal, sleeping in the daytime and hunting or foraging at night, new data suggests. With the dinosaur gone, they switched to living in daylight.
Researchers used computer algorithms to analyse details from
2,415 species of living mammals to reconstruct the activities of their ancestors.
They found that when the dinosaurs were wiped out, previously nocturnal mammals shifted to an intermediate stage of mixed day and night living that lasted for millions of years, before changing to live primarily in the daylight.
‘‘We were very surprised to find such close correlation between the disappearance of dinosaurs and the beginning of daytime activity in mammals, but we found the same result unanimously using several alternative analyses,’’ said Roi Maor, the report’s lead author and a doctoral student at UCL.
The team found that the ancestors of gorillas and gibbons were the first to give up their nocturnal activity, a discovery which fits in with the fact that their descendants - which include humans - are the only mammals that see well in daylight.
Their vision and colour perception is comparable to those of diurnal reptiles and birds - groups which never left the daytime.
‘‘It’s very difficult to relate behaviour changes in mammals that lived so long ago to ecological conditions at the time, so we can’t say that the dinosaurs dying out caused mammals to start being active in the daytime,’’ said Prof Kate Jones, the report’s co-author.
‘‘However, we see a clear correlation in our findings.’’
The research was published in the journal Nature Ecology and Evolution.