According to the “nocturnal bottleneck” hypothesis proposed in 1942, mammals could have been able to survive in a dinosaur-dominated era by avoiding the sharp-toothed beasts during the day and coming out at night. That means the first mammals evolved during the reign of the dinosaurs by adopting a nocturnal lifestyle that helped them to remain safe. But the latest study has revealed another interesting thing about dinosaur era mammals. It found out that after dinosaurs became completely extinct from the planet, some mammals began to come out during the night and started adopting themselves to the daylight which was quite important for their survival.

The research discovered that the first mammals to be active during both day and night appeared around 65.8 million years ago, just 200,000 years after the extinction event that led to the wiping out of most dinosaurs. The researchers predicted that these mammals were most likely the ancestors of the even-toed ungulates, just like today’s cattle, llamas, and hippopotamuses, as well as the cetaceans like dolphins and whales.

The lead author of the paper, Roi Maor, a doctoral student at Tel Aviv University in Israel said that, in evolutionary time, 200,000 years is hardly anything. It is almost immediately. He and his teammates also found out that the first clearly diurnal or only active during the daytime mammals appeared about 52.4 million years ago- some 13 million years after the dinosaurs were gone. For the research, a team of scientists constructed multiple family trees(phylogenies) based on the 2,415 species of mammals that are alive today.

  1. David Polly, an Adjunct Professor of Biology and Anthropology at Indiana University who wasn’t involved in the new study, said that the study used the evolutionary relationships to determine when mammals started moving around in the daylight. Both of the phylogenic timelines constructed by the scientists provided the same conclusion, that is, mammals switched over to the diurnal mode only after the dinosaurs were gone.

Roi Maor said that they were very surprised to find such close correlation between the disappearance of dinosaurs and the beginning of daytime activity in mammals and also they found the same result unanimously using alternative analyses. Study co-author Kate Jones said that it is very difficult to relate behavior changes in mammals that lived so long ago to ecological conditions at the time, so they can’t say that the dinosaurs dying out caused mammals to start being active in the daytime. But they see a clear correlation in their findings.


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