Dinosaurs, Mammals and survival at the KT boundary

Adrian wrote:

rosbourne979.

I'm not for a second saying that size was the deciding factor. My point was that metabolism doesn't seem to have been the deciding factor either, if it were then you would expect that the reptiles in general would have died out. They didn't, only the dinosaurs did.

Hi Adrian,

It's interesting isn't it.

Some of the reptiles died out, like all the flying pterosaurs.

From a metabolic perspective, I actually would have expected reptiles to do pretty well. One of the main challenges to warm bloodedness is that you have to eat almost constantly. The reptiles (at least some of them) don't have that need (snakes, lizards, turtles, crocks), many of them can become dormant for a long time.

It makes me wonder if the flying reptiles were actually warm blooded to some degree (a special form of reptile).

Maybe those with a subterranean life style survived better, and no dinosaurs had such a lifestyle? Mammals and bats probably had a large subterranean contingent, as well as the ability to hibernate. Maybe dino's couldn't hibernate?

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talk72000 wrote:

The large plant eating dinosaurs would have starved and died out and so would the therapods that fed upon them.

Agreed. But that leaves the small dino's. The small ones certainly weren't eating the large herbivores, unless they were all scavengers on kills from the larger ones. But their morphology suggest otherwise.

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rosborne979 wrote:

From a metabolic perspective, I actually would have expected reptiles to do pretty well. One of the main challenges to warm bloodedness is that you have to eat almost constantly. The reptiles (at least some of them) don't have that need (snakes, lizards, turtles, crocks), many of them can become dormant for a long time.

Maybe the reason we note that reptiles can become dormant is because the ones that couldn't died off then

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stuh505 wrote:

rosborne979 wrote:
From a metabolic perspective, I actually would have expected reptiles to do pretty well. One of the main challenges to warm bloodedness is that you have to eat almost constantly. The reptiles (at least some of them) don't have that need (snakes, lizards, turtles, crocks), many of them can become dormant for a long time.

Maybe the reason we note that reptiles can become dormant is because the ones that couldn't died off then

There were lots of reptiles which didn't make it past the KT boundary. I'm sure there ware lots of mammals which didn't make it either. And probably lots of birds as well.

But some mammals made it, some reptiles made it, and some birds made it. Yet, none of the dinosaurs made it (excpet birds which are unique in many ways), even though many dinosaurs shared characteristics (feathers, endothermy and size) like the survivors.

What made the dinosaurs unique enough to leave them with no survivors?

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rosborne,

I think you missed the point of my last comment...

Quote:

From a metabolic perspective, I actually would have expected reptiles to do pretty well. One of the main challenges to warm bloodedness is that you have to eat almost constantly. The reptiles (at least some of them) don't have that need (snakes, lizards, turtles, crocks), many of them can become dormant for a long time.

You say would have expected reptiles (dinosaurs) to do well because they don't have the need to eat constantly. You assume they don't have the need to eat constantly because the reptiles of today don't have that need and can go dormant.

I was trying to point out that perhaps this generalization about reptiles was not true in the past -- that the metabolism of dinosaurs was very high, they could not go dormant, whereas the reptiles that could go dormant survived into our age. Thus, don't rule out metabolism as a factor.

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They all laid eggs and unattended eggs do not hatch. Mammals probably survived on dinosaur eggs. Small dinosaurs were probably feathered and survived as nonavian birds like chicken, turkeys, road runners, dodo birds, ostriches, emus, etc. those far from the asteroid strike probably survived. 63 million years ago at 2-6 inches per year travel translates to 63,000,000*2/(12*3*1760) miles = 1,988 miles or roughly 2,000 miles. The Americas would be closer to Europe by 2,000 miles and India was not yet connected to Asia. The devastation from the asteroid would be more catastrophic as the land masses were closer together.

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stuh505 wrote:

You say would have expected reptiles (dinosaurs) to do well because they don't have the need to eat constantly.

Dinosaurs were not reptiles.

stuh505 wrote:

You assume they don't have the need to eat constantly because the reptiles of today don't have that need and can go dormant.

You imply that reptiles of long ago were not like reptiles of today. Are you just making a random guess. As far as I know, there is no evidence or indication that the basic nature of reptiles from the past was much different from the basic nature of reptiles of the present.

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talk72000 wrote:

They all laid eggs and unattended eggs do not hatch.

What makes you think they were unattended?

Are you suggesting that it was 'egg laying' which made the dinosaurs so vulnerable at the KT boundary? Birds lay eggs and they survived. Reptiles also lay eggs and they survived.

talk72000 wrote:

Small dinosaurs were probably feathered and survived as nonavian birds like chicken, turkeys, road runners, dodo birds, ostriches, emus, etc.

Birds survived. No small dinosaurs survived. If they did, they would probably be here today, and we wouldn't.

talk72000 wrote:

The devastation from the asteroid would be more catastrophic as the land masses were closer together.

Possibly. But that particular impact would probably have been catastrophic no matter what the land mass configuration. And the configuration wasn't that different than it is today:

http://img48.imageshack.us/img48/1052/map66mapi1.jpg

And dinosaurs lived in the antarctic at that time. They were well dispersed and well adapted.

Dino's may have already been under stress from other sources as well, and volcanic activity (Deccan Traps) may have predated the impact somewhat. But since the extinction event affected both land and oceanic life, a reduction in sunlight is about the only thing which can account for both. Whether that reduction was a result of volcano's or asteroids, or some combination of the two, I'm not as interested in with this thread. I'm more interested in understanding the morphology or behavior which made the dino's uniquely susceptible, even while birds, mammals and reptiles had survivors. Out of that combination, there seems to be very little which was notably unique about the dino's.

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For a long period dinosaurs were at the top in almost all the niches they inhabited. This would have pressured the mammals, birds and reptiles to become more generalist in nature. Perhaps the fact that the dinosaurs were specialists was what brought them undone when things changed. The generalists were better able to adapt to new circumstances and then proceeded to out compete the dinosaurs.

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Adrian wrote:

For a long period dinosaurs were at the top in almost all the niches they inhabited. This would have pressured the mammals, birds and reptiles to become more generalist in nature. Perhaps the fact that the dinosaurs were specialists was what brought them undone when things changed. The generalists were better able to adapt to new circumstances and then proceeded to out compete the dinosaurs.

Hmmm, I'll have to think about that. At least it's unique, I don't think I've heard it before.

It seems to me that despite dino specialization, there would have been many (especially the small ones) who were less specialized. But it's not easy to quantify.

Your conjecture: All Dino's were uniquely specialized enough to eliminate them completely as a result of this particular environment change.

Did their genetic structure lack diversity? Or was it just their behavior and morphology?

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rosborne979 wrote:

stuh505 wrote:
You say would have expected reptiles (dinosaurs) to do well because they don't have the need to eat constantly.

Dinosaurs were not reptiles.

Yes they were!

rosborne979 wrote:

stuh505 wrote:
You assume they don't have the need to eat constantly because the reptiles of today don't have that need and can go dormant.

You imply that reptiles of long ago were not like reptiles of today. Are you just making a random guess. As far as I know, there is no evidence or indication that the basic nature of reptiles from the past was much different from the basic nature of reptiles of the present.

No, YOU tried to disprove a theory by assuming that reptiles were quite the same as reptiles of the present. However, like I pointed out, if the theory were correct, the reptiles of the past would not be the same...so you obviously cannot use that assumption in any part of your argument.

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stuh505 wrote:

rosborne979 wrote:
stuh505 wrote:
You say would have expected reptiles (dinosaurs) to do well because they don't have the need to eat constantly.

Dinosaurs were not reptiles.

Yes they were!

No. They are not.

Reptiles and Dinosaurs have a common ancestor, but the dinosaur line did not branch from the reptile line.

We have a thread we already did on this somewhere. I'll try to find it.

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I know this isn't a good reference but:
http://dml.cmnh.org/2000Apr/msg00382.html

This question is asked many times on google and the answer everyone gives is 'yes'..

Anyway, even if they are not, reptile is just a name...and it does not really affect the discussion

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stuh505 wrote:

I know this isn't a good reference but:
http://dml.cmnh.org/2000Apr/msg00382.html

This question is asked many times on google and the answer everyone gives is 'yes'..

Anyway, even if they are not, reptile is just a name...and it does not really affect the discussion

I was mistaken. You are correct. Dinosaurs are part of the reptile line, as are birds.

Here is the link to the Other Thread.

Surprisingly, this was my own thread, which I thought I learned something from, but apparently I forgot what I learned shortly after I learned it Smile

Anyway, so Dinosaurs are part of the reptile line, so where were we again?

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rosborne, I was also mistaken when I said you "tried to disprove a theory by assuming that reptiles were quite the same as reptiles of the present." I got you confused with Adrian.

Basically I think the major cause was this: less sunlight, lots of vegetation dies out, the large herbivores cannot sustain themselves, and then the large carnivores that depend on large herbivores also die out.

Strong selective pressure is put on the small and medium sized creatures, too, just not enough as the large ones. There may be additional pressure on the dinosaurs for being cold blooded and lacking in fur, both aspects would be detrimental when things got colder.

Adrian says that only the dinosaurs died out, and not the other large reptiles. I disagree with this basic statement. The very large reptiles were all dinosaurs. No very large reptiles have survived at all. Most of the small reptiles, of all sizes, have died.

The ones that did survive can be explained easily by saying that they were simply the best in their niches, and due to the increased selective pressure, most things had to die off. What are the largest reptiles that survived? The crocodiles? Unlike the dinosaurs that run around on land, the crocodile doesnt have to spend much energy lounging around in a swamp all day, so he requires less energy...and everything has to drink water, so it doesn't really matter to him if 50% of his prey died out, because the other 50% will still be coming to get a drink, and 1 will last him a long time.

It is not surprising that the birds did well either. Their feathers keep them warmer, and they were much smaller in size than the large pterodactyls. The pterodactyls could not fly incredibly high, and would have been targeted by the large carnivores as their regular ground-based food supply ran out. Additionally, by having feathers and using wingbeats, they are MUCH more maneuverable and harder to catch by land predators.

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That makes a lot of sense. One problem though is that they keep coming up with more and more feathered dinosaurs. Last I knew, even T-Rex was thought to look like a great big chick (in the fluffy down sense). I think it's been pretty well established that Velociraptors had feathers.

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sozobe wrote:

That makes a lot of sense. One problem though is that they keep coming up with more and more feathered dinosaurs. Last I knew, even T-Rex was thought to look like a great big chick (in the fluffy down sense). I think it's been pretty well established that Velociraptors had feathers.

sozobe, it is an interesting question, why would land-based lizards have feathers...but this is not a problem with the theory i proposed.

The most likely reason for having feathers on these ground based lizards is for show -- scare tactics and mating rituals. We know that many reptiles had bone crests, perhaps these were also adorned with feathers that could be raised in some kind of signal.

I have not heard of this before. However, feathers evolved from fur...so if velociraptors and tyrannosaurs had feathers, they must have had hair first.

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I don't think so. I'm not sure about that part, though.

What I'm addressing is more this part:

stuh wrote:

There may be additional pressure on the dinosaurs for being cold blooded and lacking in fur, both aspects would be detrimental when things got colder.

If they had feathers, that would have offered some protection. Still, maybe not enough.

It's also at least questionable whether they were in fact cold-blooded. Nothing too definite.

Quote:

Were dinosaurs warm-blooded?

Scientists have conflicting opinions on this subject. Some paleontologists think that all dinosaurs were "warm-blooded" in the same sense that modern birds and mammals are: that is, they had rapid metabolic rates. Other scientists think it unlikely that any dinosaur could have had a rapid metabolic rate. Some scientists think that very big dinosaurs could have had warm bodies because of their large body size, just as some sea turtles do today. It may be that some dinosaurs were warm-blooded. The problem is that it is hard to find evidence that unquestionably shows what dinosaur metabolisms were like.

http://pubs.usgs.gov/gip/dinosaurs/warmblood.html

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sozobe wrote:

It's also at least questionable whether they were in fact cold-blooded. Nothing too definite.

I have always felt that the evidence for warm bloodedness was quite stong (I think I mentioned capilary density of bone marrow earlier in this thread).

I guess the key remaining question is "how was the life of small dinosaurs different from small mammals?". And how did this difference lead to the extermination of even small, feathered, warm blooded (similar metabolism to mammals) dinosaurs, when small, furred, warm blooded mammals survived?

The original point of this thread is that at the time of the KT extinction, there seems to have been relatively little difference between the survivors, and the "extinctors".

Some Dinosaurs were warm blooded, Mammals were warm blooded.
Some Dinosaurs were small, Some Mammals were small.
Some Dinosaurs had feathers (down), Mammals had fur (fluff).
Some Dinosaurs ate eggs, Some Mammals ate eggs.
Dinosaurs were robust and diversified, Mammals were robust and diversified.

The differences between the two groups are not dramatic, and yet the result was.

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You don't think what?

I agree that feathers would have offered some insulation. However, I intentionally overlooked this as a possible cause for feathers to have evolved on [some] dinosaurs, because we know that feathers evolved from hair, and thick hair provides better insulation than feathers do. I suppose it is not impossible that feathers evolved separately from scales as well, but I find this very unlikely, especially since they have found evidence of hair on some dinosaurs.

Quote:

It's also at least questionable whether they were in fact cold-blooded. Nothing too definite.

Can't really argue with that, although I might add that had they been warm-blooded they would have had some distinct advantages, and given the amount of time that they had to evolve we should expect them to have evolved into the local optimum form...which does not appear to be cold-blooded.

ros, I still don't understand why you keep ignoring the major difference: everything big died.

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Dinosaurs, Mammals and survival at the KT boundary

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