Mammals Literally Came Out of the Dark Once the Dinos Were Gone

[n2doc]

The first mammals emerged during the reign of the dinosaurs, adopting a nocturnal lifestyle to stay safe. It was only until the dinosaurs were wiped off the face of the planet that certain mammals began to assert themselves during the daylight hours, according to new research.

New evidence published in Nature Ecology & Evolution suggests that the first diurnal (daytime) mammals emerged at some point between 52 to 33 million years ago. The timing would suggest that mammals had been “stuck” in a nocturnal mode of existence during the reign of the dinosaurs, which ended some 66 million years ago, and that the sudden disappearance of dinos allowed mammals to assert themselves during the day. The new study improves our understanding of mammalian evolution, but other researchers say more evidence is required for us to be absolutely certain about the timing of this important transition.

Mammalian fossils dating back to this period are hard to come by, but even if paleontologists and evolutionary biologists had tons of fossils, it would still be hard to discern an animal’s behavior from a pile of bones—including whether or not an animal was active during the day or night. That said, scientists are reasonably confident, based on the scant fossil evidence they do have, that the first mammals were nocturnal. They’re just not sure when our distant ancestors first started to emerge from the darkness.

To get a better sense of when this happened, a team of researchers from the University of College-London and Tel Aviv University constructed multiple family trees (phylogenies) based on the 2,415 species of mammals alive today.

more
https://gizmodo.com/mammals-literally-came-out-of-the-dark-once-the-dinos-w-1820177871

[lapfog_1]

1. even now, most mammals only see black and white

but some, descendants of the first fruit eaters, learned to see colors as the fruit would change color (co-evolution) to indicate it was ready to be eaten and therefore spread the seeds out.

[hunter]

5. Here's a discussion about color vision in mammals from a few years ago...

https://www.democraticunderground.com/?com=view_post&forum=1228&pid=22035

[marylandblue]

2. Some diurnal mammals have poor vision but strong senses of smell

Another holdover from our nocturnal roots.

[NickB79]

3. Alternate hypothesis: they were nocturnal due to excessive daytime heat

It's interesting that birds, the last remaining dinosaur lineage, can handle wet bulb temps up to 41F, while most mammals die above 37F. This would explain why mammals were nocturnal and mostly tunnel dwellers during the time of dinosaurs, escaping the heat and humidity as much as the therapod predators.

This would also explain why nocturnal habits took so long to change: the Eocene Thermal Maximum after the KT extinction event kept the planet warm enough to see palm trees in the Arctic Circle. It appears daytime habits evolved around the same time the planet finally started to cool down.

[cstanleytech]

4. That or because the dinos considered them a tasty treat. nt