Impact that killed the dinosaurs?

[chornedsnorkack]

Hesperornithides could not fly at all, so they could not have been affected by bad weather for flying. Yet they also died. So what was the problem for them? Lack of fish in the sea?

 

[JimC]

Dunno, could be. I haven't paid that much attention to them, so don't have an opinion.

 

[chornedsnorkack]

Dunno, could be. I haven't paid that much attention to them, so don't have an opinion.

Note that mosasaurs also were flightless, and also died.
Who besides pterosaurs ate fish?

 

[JimC]

I've read that pretty much everything that weighed more than about 40 pounds died. I think maybe that doesn't imply that everything that weighed over 40 pounds was a piscavore.

 

[chornedsnorkack]

I've read that pretty much everything that weighed more than about 40 pounds died. I don't think that implies everything that weighed over 40 pounds was a piscavore.

But a lot of animals under 40 pounds died, too. Like, all enanthiornithes - who were all under 40 pounds.
Maybe it is better to look at niches not weight?

 

[JimC]

I've not looked at weight at all, except as it applies to biomechanics of flighted animals. What nailed the pterosaurs of all weights was a period of time when conditions weren't suitable for soaring, and they couldn't travel by flapping alone.

I don't really care much about the other critters. There seem to have been enough various causes to whack most of them.

 

[chornedsnorkack]

I've not looked at weight at all, except as it applies to biomechanics of flighted animals. What nailed the pterosaurs of all weights was a period of time when conditions weren't suitable for soaring, and they couldn't travel by flapping alone.

I don't really care much about the other critters. There seem to have been enough various causes to whack most of them.

For me, the logical way to look at the various causes of extinctions is to look at the survivors - all survivors, of all groups - and their niches, and compare them with nonsurvivors - again, all nonsurvivors, of all groups - and their respective niches.
It is not obvious for me that there would have been a period unsuitable for soaring. If there had been, there would have been the niche issue - pterosaurs could fly to travel, but did all of them need long distance travel to feed? As you suggest, they were poorly suited to feed while walking.
But the disappearance of other (nonflying) piscivores suggests an alternative - they could fly, but fish were scarce wherever they flew.

 

[JimC]

Does the shortage of fish also explain the demise of the insectivores?

 

[chornedsnorkack]

Does the shortage of fish also explain the demise of the insectivores?

No, but both of them may have had common causes.
A lot of the insects have preadaptations to handle bad seasons - as dormant adults burrowed somewhere, eggs, pupae...
Do "insectivores" refer to animals who depend on active, perhaps flying insects?

What did adult pterosaurs do for bad seasons - migrate longhaul? That would have broken down if, for once, it was a bad season in tropics, too.

 

[Brian G Turner]

Close enough - much of it was. That visualization tool assumed that all energy was retained within the atmosphere. In actuality thank god, quite a bit of it was immediately ejected back into space. It also assumed that the energy was distributed uniformly. Again thank god, it wasn't. It's still a durned good tool for visualizing the total amount of energy involved.

The scientific consensus is that any asteroid strike would not have had enough energy to cause a global extinction event. I perhaps should underline that.

I've read that pretty much everything that weighed more than about 40 pounds died. I think maybe that doesn't imply that everything that weighed over 40 pounds was a piscavore.

Everything that was a dinosaur, perhaps? But certainly not everything else: crocodiles, turtles, sharks, and other fish. Or trees, and other large plants.

Which is quite impressive, because their modern descendants struggle to survive a just couple of degree rise in global temperatures over a century, yet apparently their ancient ancestors managed to survive an asteroid strike that could sever limbs halfway around the world, create tsunamis bigger than mountains that raced across the globe, and survived thousands of years of nuclear winter which stopped even photosynthesis from working!

Heck, the more I read about this asteroid impact, the more it sounds like some alien Noah's Ark must have come down and collected everything except the dinosaurs!

That's if you accept the increasingly strained attempts to make the impact theory the major cause of the end-Cretaceous mass extinction.

 

[JimC]

Personally I think it was a combination of the two impacts plus the Traps. But Chicxulub alone was sufficient for a global event.

 

[Brian G Turner]

Btw, I've moved the discussion of pterosaur physiology into it's own dedicated thread here:

Pterosaur physiology

"Recent articles on the impact theory have stated that the Chicxulub event would not have had sufficient energies to cause the global devastation postulated in the classic model," What is the energy range currently estimated for the impact? How many simultaneous Tzar Bombas would that be...

www.sffchronicles.com

 

[Matteo]

I thought the theory was that the largest fauna (and dinosaurs were getting larger, I think) were wiped out partly due to the asteroid impact and partly due to the subsequent lack of food.

Smaller creatures, especially the mammals, were able to survive better because many were burrowing (so "sheltered" from the after eggects) and because there was more (relatively) food around for longer - and they were omnivorous.

Plants are very hardy and domant seeds recovered quickly.

And I'm sure I read a paper linking the Deccan Traps eruptions to the asteroid impact.

But I'm on my fourth Czech beer of the day so I may be remembering all the above wrong

 

[Matteo]

OK, scratch all the above.

I've just read a new theory at the place I'm posting this from...

 

[JimC]

"The scientific consensus is that any asteroid strike would not have had enough energy to cause a global extinction event. I perhaps should underline that."

Seems like you and Gerta Keller are about the only two people who believe that.

 

[chornedsnorkack]

End-Mesozoic extinction was massive. Even the groups that survived lost species... and it seems that the species that survived lost individuals.
And yet it was selective - some large groups were wiped out, others passed with a number of taxa.
Also note that more taxa survived into Cenozoic than had survived into Mesozoic - and it had not been an impact that time.

 

[Vertigo]

The scientific consensus is that any asteroid strike would not have had enough energy to cause a global extinction event. I perhaps should underline that.

I'm really not convinced that is the consensus. Most reports I have read from science.org to the Natural History museum seem to conclude that it would have had sufficient energy. Traces of it are found distributed all across the globe. However with the coincident Deccan Traps it certainly had some help, needed or not.

 

[Brian G Turner]

Most reports I have read from science.org to the Natural History museum seem to conclude that it would have had sufficient energy.

Seems like you and Gerta Keller are about the only two people who believe that.

It's long been known that the energy of the Chicxulub impact was not enough to cause a mass extinction. This is a scientific fact that even those who support the idea that the impact was the sole cause the extinction event freely state. Instead they cite additional circumstances that might have caused the impact to have a more exaggerated effect, such as that the impact might have passed some otherwise unknown energy threshold, or that it hit a rich bed of methyl hydrates to add to the explosive power, or that it hit particularly sulphur-rich rocks to cause the additional required atmospheric disturbance to cause the extinction - all of which is simply speculation rather than scientific fact.

Here's one such citation:

New analysis of Chicxulub asteroid suggests it may have struck in vulnerable spot

(Phys.org)—A pair of researchers at Tohoku University has found evidence suggesting that if the asteroid that struck the Earth near Chicxulub 66 million years ago had landed almost anywhere else, it would not have been nearly as destructive. In their paper published in the journal Scientific...

phys.org

if the asteroid that struck the Earth near Chicxulub 66 million years ago had landed almost anywhere else ... it is likely the dinosaurs would have survived.

Note that this approach of pushing for the asteroid impact as the key extinction event is a situation of trying to force the facts around the theory, rather than let observation shape one.

If you look at any area of academia, there are always competing theories and controversies. The popular paradigm - which the media always primarily report - in this instance, over the past few decades, has been that an asteroid impact single-handedly caused the death of the dinosaurs. It's a simple and dramatic explanation, and it's great for the public imagination. But there's no science behind anything other than the impact happening, not the consequences of it.

The emerging popular view is that the eruption of the Deccan Traps determined the extinction event, and the Chicxulub impact simply gave this an extra kick. This is the point I raised in my original post/rant 20 years ago, and it's also the consensus view I mentioned a few posts back. I think it's also one you mentioned you thought was accepted. However, pretty much every media report on the issue will always promote the idea that an asteroid impact killed the dinosaurs, and any reference to the Deccan Traps eruptions is generally down-played. EDIT: The Wikipedia entry has this to say: "In March 2010, an international panel of 41 scientists reviewed 20 years of scientific literature and endorsed the asteroid hypothesis, specifically the Chicxulub impact, as the cause of the extinction, ruling out other theories such as massive volcanism."

The idea that "an asteroid killed the dinosaurs" is so prevalent in the public and scientific imagination that we've had researchers looking for a single impact to explain each of the other big extinction events, even though they are all associated with extreme levels of volcanism whose processes are well-known and documented. This is especially relevant because it's been suggested that the rates of CO2 released by human activity since the industrial resolution are equivalent to those same events.

 

[JimC]

"I'm really not convinced that is the consensus. Most reports I have read from science.org to the Natural History museum seem to conclude that it would have had sufficient energy".

Most of us who work with this stuff communicate more by email, phone, and verbal exchanges over a beer or three than by written reports. Nearly as I can tell, the overwhelming consensus is that the impact power was more than sufficient -- but it did get a lot of help from the traps.

 

[Brian G Turner]

And another study being published, that belongs to the "we know only an asteroid could have killed the dinosaurs, we just can't make the evidence fit" - aka, we have a bias and we insist on trying to prove that it's true despite the lack of supporting evidence.

Asteroid dust caused 15-year winter that killed dinosaurs: Study

Around 66 million years ago, an asteroid bigger than Mount Everest smashed into Earth, killing off three quarters of all life on the planet—including the dinosaurs.

phys.org

Around 66 million years ago, an asteroid bigger than Mount Everest smashed into Earth, killing off three quarters of all life on the planet—including the dinosaurs.

This much we know.

But exactly how the impact of the asteroid Chicxulub caused all those animals to go extinct has remained a matter of debate.

The article goes on to saw that the most recent popular ideas are that the impact just happened to hit rocks particularly rich in sulfur, which managed to create a massive acidic cloud similar to what you might see from a mass volcanism event, thus causing the Cretaceous extinction; another idea being that the impact caused a massive fire storm that effectively burned up the world's vegetation overnight, causing a layer of soot that blocked out sunlight for years.

This latest study now throws back to an older theory, which is that it was nothing more than silicate dust caused by the impact and filling the atmosphere that caused a nuclear winter effect.

As is common with these studies, it's a US team looking at limited US records and applying them globally - in this instance, finding particles of silicate dust at a particular fossil site in Dakota. They then make estimates and put it into a computer model to reach their foregone conclusion. But as the article points out near the end, even then it doesn't provide any definitive answers.

In the meantime, northern China is suffering from a particularly bad bout of smog, with visibility reduced to around 50 metres:

Northern China chokes under severe pollution

Tens of millions of people across northern China were under severe pollution warnings Tuesday, with authorities urging them to reduce outdoor activities as a grayish smog enveloped the region.

phys.org

Imagine how ironic it would be if researchers in the far future took samples from around Beijing of this period, and used it to prove that - in our time period - that same cloud of smog covered the entire world?

We have plenty of evidence that millions of years of volcanism at the Deccan Traps caused an extinction event that the asteroid impact helped to finish off. I find it strange how some scientists find that hard to accept and insist it's the asteroid or nothing. Maybe the idea of an asteroid impact just has too much dramatic appeal compared to some boring old smoking volcanoes?