Dinosaurs, Mammals and survival at the KT boundary

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Conventional wisdom says that small mammals crawled from holes to dominate the decimated world left after the demise of dinosaurs.

But mammals were not so small and insignificant as conventional wisdom portrays.

Bats were already highly specialized by the Cretaceous, and other mammals were quite large. "Devil Dogs" have been found with dinosaurs in their stomachs.

If mammals were both large and small, and dinosaurs were both large and small, then what was it about the mammals which allowed them to survive when the dino's (except for the birds didn't)? Was it more about metabolism than size?

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This is purely speculative, but all the matter thrown into the atmosphere would have really obscured the sun. For cold blooded reptiles that rely on basking in the sun to keep their blood warm, they may have just gotten too cold to survive or just lost the energy to maintain a competetive edge.

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Yup. I'd think the warm blooded-cold/cold-blooded thing could play into it. Mammels could have dominated the colder regions while Dino's dominated the warmer climes. As the warmer regions cooled the mammels could have "moved in" expanding their range.

I've never really thought about it and have no idea how that would match up with the fossil record and such but it seems plausible off hand.

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It's a great question, especially since I wasn't aware that any mammals existed of any significant size. I had the image of little shrew-like animals scampering around catching insects. As of yet I don't have any suggestions. I'm still trying to come to grips over the Pleistocene extinctions.

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stuh505 wrote:

This is purely speculative, but all the matter thrown into the atmosphere would have really obscured the sun. For cold blooded reptiles that rely on basking in the sun to keep their blood warm, they may have just gotten too cold to survive or just lost the energy to maintain a competetive edge.

I believe many of the therapod dinosaurs were actually warm blooded. Their bone structure (including R-Rex) shows growth patterns and circulatory patterns indicative of warm bloodedness.

It could be that after the reduction in sunlight, it was just much easier to be small, and maybe mammals were better at being small than dinosaurs, even though they both had a range of sizes.

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rosborne979 wrote:

I believe many of the therapod dinosaurs were actually warm blooded. Their bone structure (including R-Rex) shows growth patterns and circulatory patterns indicative of warm bloodedness.

It could be that after the reduction in sunlight, it was just much easier to be small, and maybe mammals were better at being small than dinosaurs, even though they both had a range of sizes.

Fur is good insulation, too.

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stuh505 wrote:

rosborne979 wrote:
I believe many of the therapod dinosaurs were actually warm blooded. Their bone structure (including R-Rex) shows growth patterns and circulatory patterns indicative of warm bloodedness.

It could be that after the reduction in sunlight, it was just much easier to be small, and maybe mammals were better at being small than dinosaurs, even though they both had a range of sizes.

Fur is good insulation, too.

Yes it is. And so are feathers. And many dinosaurs had feathers.

There's probably no single answer to the question of why mammals survived and dinosaurs didn't. But I thought it was interesting to realize that some of the 'old' conventional wisdom about mammals being little squeeky things who were not as 'evolved' as dinosaurs is probably very inaccurate.

Mammal like animals had been around almost as long as the dinosaurs, and many mammals were probably very specialized (like bats, which also survived the KT extinction). The 'rise' of the mammals after the KT wasn't so much of a 'rise' as it was an 'explosion' in diversity of pre-existing forms.

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rosborne979 wrote:

Yes it is. And so are feathers. And many dinosaurs had feathers.

There's probably no single answer to the question of why mammals survived and dinosaurs didn't.

Eh? We still have birds...

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The 'rise' of the mammals after the KT wasn't so much of a 'rise' as it was an 'explosion' in diversity of pre-existing forms.

Well, this is guaranteed to happen whenever there is a mass extinction. There may be a lot of randomness as to which species prevail in such a situation.

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Most non dinosaur reptiles seem to have survived as well. That makes it more confusing.

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Adrian wrote:

Most non dinosaur reptiles seem to have survived as well. That makes it more confusing.

Not really, it is only the large inefficient monsters that disappeared. Gigantic creatures weighing many tons need to consume lots of energy. If resources are low, a small lizard may still be able to find enough to get by, but the huge beasts will not. The big guys are also very interdependent on each other. Because they are big and loud, they will only get sustainable energy from other big things, and aren't equipped to hunt the small prey anyway. If the vegetation isn't doing so hot, the big vegetarians die off, the big predators die off, the little guys are still doing ok.

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i think it was the fact that the dinosuars just figured out that humans were going to come and screw up the world. so why wait, just go ahead and roll out before they were hunted to death for sport, killed off by pollution, or done in by the global warming that the pollution caused... either way, they were the smart ones.

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stuh505.

I don't think you get my point. Metabolism can't have been the major factor, otherwise reptiles in general would have died out. They didn't, only the dinosaurs. Not just the "large inefficient monsters", all of them. There were plenty of large reptiles that survived, but no dinosaurs. Dinosaurs may have been warm or cold blooded, or a mixture of both, either way they died out. Mammals, birds and reptiles, by and large, didn't.

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so could someone tell me the difference then between a reptile and a dinosuar?

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It's all in the hips baby.

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Adrian wrote:

stuh505.

I don't think you get my point. Metabolism can't have been the major factor, otherwise reptiles in general would have died out. They didn't, only the dinosaurs. Not just the "large inefficient monsters", all of them. There were plenty of large reptiles that survived, but no dinosaurs. Dinosaurs may have been warm or cold blooded, or a mixture of both, either way they died out. Mammals, birds and reptiles, by and large, didn't.

All the dinosaurs died out because we only gave the name dinosaur to the ones that arent alive anymore. But we've still got turtles and lizards and birds...so what is your aversion to calling these the "small dinosaurs that lived"

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Adrian wrote:

stuh505.

I don't think you get my point. Metabolism can't have been the major factor, otherwise reptiles in general would have died out. They didn't, only the dinosaurs. Not just the "large inefficient monsters", all of them. There were plenty of large reptiles that survived, but no dinosaurs. Dinosaurs may have been warm or cold blooded, or a mixture of both, either way they died out. Mammals, birds and reptiles, by and large, didn't.

And many dinosaurs were very small. They aren't as famous as their larger cousins, but they were there.

Size doesn't seem to be the deciding factor.

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Seed wrote:

so could someone tell me the difference then between a reptile and a dinosuar?

Reptiles are cold blooded for one thing. They also have a distinct geneology which is different than the dinosaurs.

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stuh505 wrote:

All the dinosaurs died out because we only gave the name dinosaur to the ones that arent alive anymore. But we've still got turtles and lizards and birds...so what is your aversion to calling these the "small dinosaurs that lived"

Birds are the only dinosaurs which survived. The other animals you mentioned are reptiles.

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stuh505.

Turtles and lizards aren't dinosaurs. Birds are but they had already branched off by they time dinosaurs died off. There were small dinosaurs around, as rosbourne mentioned, and they died out along with the big ones. Birds and lizards of an equivalent size did not.

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.

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Yes, don't forget the huge asteroid that plummeted into the Gulf of Mexico. The crater is hundreds of miles in diameter. It must have penetrated the crust so lava must have gushed out and water flew up into the stratosphere and beyond. There would have been monstrous tsunamis several hundred feet in height. Thetsunamis would behuge killers. Most of the land was probably forested so huge fires would have consumed the trees. The asteroid would have created pressures in the molten interior and weak points in the earth's crust would have developed volcanos like the Deccan Plateaux in India. The asteroid would have been diverted by the iron core center. The fires would have created so much smoke and with the volcanic explosions in the Deccan Plateaux, the atmosphere would be acrid and headly breathable. Not sure how long those conditions would have lasted, probably years - look at Mt. St. Helens(?) in Washington State.

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

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Dinosaurs, Mammals and survival at the KT boundary

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