'Gorillas, gibbons first mammals to embrace daytime activity'

New York: The ancestors of simian primates such as gorillas, gibbons and tamarins, were among the first mammals to embrace daytime activity, finds a new study, challenging a long-standing theory that the common ancestor to all mammals were active at night.

The study showed that mammals shifted to daytime activity shortly after the dinosaurs had disappeared, about 66 million years ago. 

"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 lead author Roi Maor, a doctoral student at the Tel Aviv University in Israel.

"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. However, we see a clear correlation in our findings," added Kate Jones, professor at the University College London.

Moreover, the discovery fits well with the fact that simian primates are the only mammals that have evolved adaptations to seeing well in daylight. 

The visual acuity and colour perception of simians is comparable to those of diurnal reptiles and birds -- groups that never left the daytime niche, the researchers said.

For the study, published in the journal Nature Ecology and Evolution, the team analysed data of 2,415 species of mammals alive today using computer algorithms to reconstruct the likely activity patterns of their ancient ancestors who lived millions of years ago.

However, the shift must have involved an intermediate stage of mixed day and night activity over millions of years, which coincided with the events that decimated the dinosaurs, the researchers noted.