Their analysis showed that the shift among some mammal species to diurnal activity happened after the extinction event. The earliest mammals that were strictly diurnal included simian primates, around 52 million to 33 million years ago. Though scientists can't say that one caused the other, the study provides fresh circumstantial evidence.
However, it also appears that cathemeral activity (operating partly during both day and night) may have emerged much earlier, roughly 9 million years before the dinosaurs disappeared.
If dinosaurs still dominated the daytime, then why would some mammals start to shift into that space?
There are a few possible explanations. Perhaps cathemeral mammals were trying to reduce the chances of being eaten by other mammals at night. Perhaps the emergence and spread of flowering plants (and the insects that evolved with them) provided new opportunities for mammals to flourish.
But there's also mounting evidence that dinosaurs were in decline long before the asteroid wiped them out. This may have opened opportunities for mammals to start inching into the daylight and, eventually, seizing the day.
(c)2017 Los Angeles Times
Visit the Los Angeles Times at www.latimes.com
Distributed by Tribune Content Agency, LLC.