When Mammals Only Went Out At Night

For decades, scientists believed dinosaurs were diurnal and tiny mammals were nocturnal. But as researchers have uncovered more mammalian fossils and studied the biology of different dinosaur species, they’ve found some surprising results.

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[DISTurbedwaffle]

It's also worth noting how many insect species are more active at night, like crickets, and especially on warmer nights. Perhaps mammals were adapted for nocturnality to go after the wide selection of nocturnal insects.

[Xnaut]

There's one other biological factor about modern mammals that appears to be a leftover from the nocturnal bottleneck hypothesis: the inability to produce gadusol. Gadusol is a cellular metabolite in plants, fungi, and most animals that enables uv light absorption without leaving any distinct pigmentation. This is incredibly useful for any organism that spends significant amounts of time in full sun to protect dna from uv damage, and the only large collective animal taxa that can't naturally make this compound is mammals. This is highly implicative that ancient basal mammals spent so little time in daylight that producing natural sunscreen was no longer selective for long term survival by evolutionary standards and the genetic process accumulated so many deleterious mutations that mammals stop producing this staple cell product even if they began spending time out in the sun (unfortunately). This is one of the strongest points of nocturnal bottleneck for Mesozoic mammals and implies that even large species like Repanomamus couldn't live fully diurnal lifestyles even if they could directly compete with dinosaurs. Mesozoic mammals were likely most active at dawn, dusk, and night, and any species that did venture out by day still likely lived in habitats with plenty of shade or were semiaquatic like Castoracauda (please make a video about that Eons) and didn't start fully adapting to full sun niches until after the K-PG Extinction, without natural sunscreen and relying fully on melanin and dust bathing to protect against uv rays.

[SilverDawnArrow]

If dinosaurs are responsible for the tiny panther that lives in my house then that's just one more thing to love them for

[thenerdbeast]

Well there is more than just eye anatomy to suggest a nocturnal bottleneck; even diurnal mammals today are a lot more sensitive to UV radiation than birds or reptiles, suggesting UV resistance genes were lost in mammals due to the nocturnal bottleneck limiting the amount of daylight they were exposed to.

[Nagassh]

I'm a complete rube, but I'd have thought the conditions post-meteor impact would be more suitable for noctournally adapted animals than diurnal ones. Doesn't seem particularly surprising that they're the ones that survived, thrived and radiated out into all the niches post-meteor and resulted in what we have now.

[Bruh-jrep]

Ah, finally I found somebody to blame for me being night owl, lol🤣

[CannaCJ]

Every Eons presenter has such clear diction, really aids in recalling the information. Thanks and kudos.

[shanechopko]

I love how you show the time period with the tectonic movements right after the intro!! I wish all your vids had the exact animation

[nicks]

Velociraptors hunting at night. Now there’s a scary thought.

[DavidPanofsky]

Is it possible that the nocturnal bottleneck effect has more to do with which mammals survived the Chicxulub impact rather than the characteristics of mammals before this extinction event?

[xJopeRz]

these videos have changed my life, i was on the wrong track, getting into the wrong crowds and activities so with the execution of educating people with talented hosts and breaking down complex topics, forever grateful thankyou

[Jacob-yglz]

Fun fact: Apes are what happened when we started evolving back in the opposite direction. The reason why human can see more colors than other mammals is because we took on a diurnal fruit eating niche, so seeing more colors at the expense of worse night vision was actually an advantage. Also, that's why apes don't have wet noses, unlike other mammals. We can see our food, so we don't have to rely so much on smell.

[alicecain]

If I could only watch one show, it would be Eons.

[King_Kristof]

Ah, so this is why we all stay up til 4am, It's Science!

[ZetaFuzzMachine]

What about burrowing? For sure that has to matter to those dark-adapted eyes!

[slwrabbits]

This was a really fascinating episode! I had no real conception of how different avian and reptilian eyes could be from mammalian ones - the differences are not well explained in the level of anatomy that I took, and most of my patients are mammals. I'd love to learn more details about the specific adaptations for diurnal avian eyes, for instance.

Please also tell Michelle that I enjoyed listening to their voice! It's very soothing and calming. They are a very clear presenter.

[bananahitler]

I would like to see a video about the time India was an Island from 100-50 million years ago, how the animals adapted to their isolation and how different was the fauna after the Kpg extinction event during the last 15 million years of its isolation.

[zooemperor]

The mammals just found it more fun to join the dark side

[zohabaig]

I wonder if the huge amounts of ash and debris in the atmosphere immediately following the KpG extinction event also selected for nocturnal mammals? I mean, if the earth was significantly darker during that time, animals adapted to hunting at night probably had a better chance of survival.

[stephanieparker]

Thank you for a great video, Michelle! I love learning about the evolutionary history of the senses like eyesight and hearing!