Mammals were nocturnal until Dinosaur extinction

[Brian G Turner]

A study reported on by New Scientist suggests that mammals were nocturnal until the dinosaur mass-extinction event 65 million years ago - and that monkeys were among the first to adapt to daylight, perhaps explaining why apes have some of the best eyesight among mammals: Dinosaur mass-extinction let mammals come out in the day

 

[night_wrtr]

I would imagine the risk of moving around during the day to be far too high during that time. With the dinosaurs gone or dying, it left the door open. Makes sense that mammals would begin their expansion at that point.

 

[Edward M. Grant]

Yes. When dinosaurs were around, any mammal who habitually went out in daylight probably died before it could reproduce. So it makes perfect sense that we'd take over the daylight once the dinosaurs were gone.

 

[Mike Donoghue]

If true, that indicates just how effective the dinosaur predators were. Was it that there were so many predators, or that there just wasn't any niches/space for more "peaceful" (mammals) animals? I wonder if advanced tool usage would have ever arisen in the dinosaurs. We know of birds that use cactus needles to spear bugs.

 

[night_wrtr]

If true, that indicates just how effective the dinosaur predators were. Was it that there were so many predators, or that there just wasn't any niches/space for more "peaceful" (mammals) animals? I wonder if advanced tool usage would have ever arisen in the dinosaurs. We know of birds that use cactus needles to spear bugs.

Hmm. Interesting thought. Dinosaur brains varied in size. Most of us have heard the walnut comparison, but many species had larger ones. The cerebrum's were small though, so that diminishes the return on complex thought. Still, we see animals today that have small brains capable of tool use. The New Caledonia Crow has a very high intelligence level and tool usage. Small brains, even in the line of descendants from dinosaurs. (If you want to read about bird intelligence I highly recommend The Genius of Birds by Jennifer Ackerman).

I think it would be possible that some species would or did have this level of intelligence.

Limited environment with an overabundance of highly efficient predators curved mammal development for sure. Just no place for them to flourish.

 

[LordOfWizards]

Related: Dinosaur-Era Fossil Shows Birds' Feathers Evolved Before Flight

I also heard recently on Nova that some large birds may have been what drove us bi-pedal hominids out of the trees.

 

[The Ace]

The theory's been around for Donkey's.

It's pretty obvious that the smaller bird-like dinosaurs would've been formidable hunters, at least in daylight ( the warm/cold-blooded argument hasn't been fully resolved), so there must've been some factor that allowed the mammals to survive.

@LordOfWizards - The birds made a grab for the niches left vacant by the dinosaurs at the same time as the mammals did. While the mammals won out in the long run, some of the large predatory birds became terrifying in size and ferocity (it's even speculated that their now useless wings (they hadn't a hope of flight) re-evolved into grasping forelimbs, but this theory remains controversial).

 

[night_wrtr]

And to add on - this article says the asteroid had a 1 in 10 chance of causing an extinction event:
Dinosaurs Might Have Survived if The Asteroid Had Hit Earth Elsewhere

Sixty-six million years ago, only 13 percent of Earth's surface contained enough organic material to generate this doomsday soot, the authors concluded in the new study.

Had the asteroid hit the other 87 percent of Earth, Kaiho said, "I think dinosaurs could be alive today."

 

[LordOfWizards]

Wow. What are the chances? (Oh, yeah. you said what the chances were.)

I'm curious, could they determine if the spot the asteroid hit was above ground at the time? (as opposed to where it is now - submerged)

 

[Brian G Turner]

this article says the asteroid had a 1 in 10 chance of causing an extinction event

This is something that has come up repeatedly with the asteroid strike - no matter how much anyone talks up the destructive force involved, it still should not have been strong enough to cause a KT extinction event.

Previously, it was claimed that the impact striking methane hydrate deposits was what turned into into one, but even still, I've always felt researchers were grasping at straws. In other words, they know the effect, and the asteroid strike looks like a probable cause so they try to find reasons why it's impact would be far greater than physics should otherwise allow.

Additionally, there have been serious arguments that the extinction event happened over something like 5 million years, rather than being sudden.

I've complained before that there used to seem like a bias in the research, with North American scientists plainly convinced that damage to North America meant must have been reflected globally - while other scientists seemed to have looked more to the mass eruption of the volcanic Deccan Traps as the actual smoking gun.

What I've not yet seen anyone suggest is that the asteroid strike could have sent a shockwave through the earth to converge on India to destabilize the Deccan Traps - not least if the latter was at the exact opposite side of the earth at the time.

 

[night_wrtr]

Wow. What are the chances? (Oh, yeah. you said what the chances were.)

I'm curious, could they determine if the spot the asteroid hit was above ground at the time? (as opposed to where it is now - submerged)

I think the consensus was partial land and sea, at least shallow seas. The wiki mentions if had hit in the deep sea, the tsunami would have been 3 miles high...

Previously, it was claimed that the impact striking methane hydrate deposits was what turned into into one, but even still, I've always felt researchers were grasping at straws. In other words, they know the effect, and the asteroid strike looks like a probable cause so they try to find reasons why it's impact would be far greater than physics should otherwise allow.

Additionally, there have been serious arguments that the extinction event happened over something like 5 million years, rather than being sudden.

Yeah, that article called it the "doomsday soot." I still think it was the catalyst that triggered a domino effect of events that lead to the mass extinctions.

 

[night_wrtr]

Another fun article says the amount of sulfuric gas released was three times what was previously thought, dropping the temperature by 47 degrees overnight: The Asteroid That Killed Dinosaurs Triggered a Worse Global Disaster Than Ever Imagined

The blast ignited global firestorms, blew hurricane-force winds for thousands of miles, crushed coastlines around the globe with massive tsunamis, and shook the entire planet, leading to massive landslides and earthquakes around the globe.

Some now-extinct species might have survived these calamities, however, were it not for a more drawn-out killer: global cooling. The dust and gases released into the upper atmosphere by the smash-up bounced much of the sun's energy back into space for years.

This dramatically chilled the planet, the thinking goes, leading to the Cretaceous-Paleogene extinction event, in which some 75 percent of lifeforms perished.

 

[Vertigo]

My understanding is that the asteroid strike was a last straw event; the dinosaurs were already in serious decline and I was under the impression that that decline was due largely to an inability to adapt fast enough to climate change.

On the advanced tool handling/intelligence theme my view is that, bearing in mind human intelligence evolved over little more than few million years and that dinosaurs were around and evolving for going on for 200 million years, they just weren't on an evolutionary track that was going to lead to intelligence. I guess if you are so well evolved for your particular niche then small incremental increases in intelligence just aren't going to give a significant advantage.

 

[night_wrtr]

The breakup of Pangaea probably had something to do with that. But I wonder, even if dinosaurs as a whole unit were on the decline, if certain species would have still flourished. And if the asteroid never hit, would mammals have still found a corner of the world to evolve. And what evolutionary path might they have gone down.

 

[Venusian Broon]

Plenty of direct descendants of dinosaurs flying about in large numbers today, so can you say they were in a 'serious decline'? Possibly if you want to restrict your view to specific large, non-avian, (perhaps) not-feathered, terrible lizards. But then you can probably say that about any animal/plant as being in decline. Look at the number of different hominid species that have disappeared in the past 4 millions years - place used to be teeming with all sorts. Now just a mono-culture!

As for intelligence, surely the jury must be out on that if it's a great evolutionary advantage. Sure we pat ourselves on the back for all the clever things we've done to become the dominant warm-blooded animal on Earth (some of the insects, bacteria and virus's must have a look-in as being pretty strong as being 'dominant' too )

But then again, we may also be stumbling half-aware into causing a large-scale extinction event and troubling climate change, as well as having the ability to willingly burn the world leaving it mostly thermonuclear ash. It's hard to say if any other single species in Earth's history has knowingly wielded such power, but my guess is that none have. Perhaps in this universe intelligence is a fragile and chaotic trait that inevitably ends in disaster and extinction?

 

[DelActivisto]

I curious, though. There were plenty of nocturnal dinosaur predators. And many predators today are nocturnal as well. So I wonder how much difference it makes? The protection of the night - except you can't see what's out there either.

 

[Venusian Broon]

I curious, though. There were plenty of nocturnal dinosaur predators. And many predators today are nocturnal as well. So I wonder how much difference it makes? The protection of the night - except you can't see what's out there either.

That's an interesting question, however it does, I think, depend on a whole number of factors that are specific to each individual species and their habitat.

Apart from the ability to go about unseen from your prey as you've said, it could be that it just is not a good idea to hunt in daylight because the heat of the sun will just exhaust you, so temperature could be a factor (depends on what part of the globe you are in, of course).

Also you may be preyed upon - say you are small mammalian insectivore - so hunting at night cuts out lots of potential predators or hampers their chances of finding you.

Possibly also you may not be able to fully compete against the alpha predator so it makes sense to hunt when either they are resting or are also disadvantaged by the lack of light.

 

[DelActivisto]

That's an interesting question, however it does, I think, depend on a whole number of factors that are specific to each individual species and their habitat.

Apart from the ability to go about unseen from your prey as you've said, it could be that it just is not a good idea to hunt in daylight because the heat of the sun will just exhaust you, so temperature could be a factor (depends on what part of the globe you are in, of course).

Also you may be preyed upon - say you are small mammalian insectivore - so hunting at night cuts out lots of potential predators or hampers their chances of finding you.

Possibly also you may not be able to fully compete against the alpha predator so it makes sense to hunt when either they are resting or are also disadvantaged by the lack of light.

I think if they dinosaurs had been more frequently nocturnal, mammals probably would have become more diurnal. My hypothesis is that mammals simply evolved a carcadian rhythm to be active when the apex predators were not active.

 

[Dave]

(I'm more of a botanist than a zoologist, and in any case, when I studied Noah was still building the Ark, so I apologise now but I genuinely don't know this and can't find the answer instantly using Google) however, can this statement be substantiated with any evidence:

There were plenty of nocturnal dinosaur predators.

It would seem to me that you would need to be homeothermic to be active at night in temperate and arctic climates. Birds and Mammals are homeothermic but Lizards are not. Is there much research on whether Dinosaurs were homeothermic? Or even Endothermic? Birds being the descendants/cousins of feathered Theropods, Ornithomimids, Ornithopods and Raptors suggests highly that they were Homeothermic, but then the back plates of the Stegosaurus suggests that they were not. I suspect that the answer is that some might be homeothermic, some were probably Endothermic and some were Ectothermic. Even if all the bird-like Dinosaurs were homeothermic, I would still take issue with use of the word "plenty."

The other thought I had was about Hibernation. Hibernation is an adaption to extreme winter temperatures without food and it would appear Mammals have it because they evolved to fill this niche of living in cold climates during the night. Birds migrate. Insects pupate. Lizards being Ectotherms don't have an adaptation. Do we know what Dinosaurs did when winter came? This would be dependent on whether they were Ectothermic, Endothermic or Homeothermic.

 

[Venusian Broon]

Good points Dave, but isn't your example of Stegasaurous of a dinosaur that is very, very ancient? An animal that existed tens (hundreds?) of millions of years before other familiar ones like T-rex and Triceratops?

Plenty of time for all sorts of mechanisms to evolve?

Also, have there not been dinosaur fossils found in Antarctica that suggest that they adapted to the continent going south and the increasingly longer nights, by adapting nocturnal traits?