WI: No K-T extinction

[Zuvarq]

Possible, but there are suggestions about that some mammals already had superior brain power ounce-per-ounce. Plus there's the issue that these tiny, apparently flexible, warm-blooded, and insulated creatures died out in the K-T, while mammals did not. There has to be a reason for it.

What I suspect is that it's the egg-laying issue. Live birth is more flexible and (usually) allows a faster birthrate. That is a powerful feature, evolutionarily speaking.

The reason they died out is because they didn't burrow like the mammals.

Though eggs vs live birth is an important point.

 

[oshron]

What I suspect is that it's the egg-laying issue. Live birth is more flexible and (usually) allows a faster birthrate. That is a powerful feature, evolutionarily speaking.

im pretty sure that some dinosaurs are believed to have live births. the one that im pretty sure of is homalocephalae (its hips are wider than most pachycephalosaurs, which led to these suggestions of live birth) and i think i heard something about live birth in troodonts but cant quite remember and have no source on that. i'll ask some friends who are more paleontologicall-informed than i am and see what they think

 

[Admiral Matt]

The reason they died out is because they didn't burrow like the mammals.

Though eggs vs live birth is an important point.

Really? How did they work that out, I wonder? One would thing that burrowing is a capability pretty widely available....

 

[Admiral Matt]

im pretty sure that some dinosaurs are believed to have live births. the one that im pretty sure of is homalocephalae (its hips are wider than most pachycephalosaurs, which led to these suggestions of live birth) and i think i heard something about live birth in troodonts but cant quite remember and have no source on that. i'll ask some friends who are more paleontologicall-informed than i am and see what they think

Please do. That'd be quite nifty if it turned out to be the case.

 

[oshron]

got some replies back. here's what they had to say:

Well no living dinosaur gives birth to live young (that I'm aware of) and we have no evidence of any of the extinct species doing so (again, as far as I know) as of yet. this doesn't make it impossible though. Some lizards give birth to live young while most lay eggs.

I was just reading something about how the structure of hard shelled eggs doesn't lend towards switching over to live birth. In most reptiles, the eggshell is soft and permeable, so it's a slippery slope between the egg shell simply not developing all the way in the mother's body to not developing at all. It could be that the evolution of the hard-shelled egg in dinosaurs was the point of no return for live birth ever evolving.

I´ve often read that idea of Homalocephale giving birth, too, but since both crocodiles and birds lay eggs we should predict all dinosaurs to lay eggs unless a fossil says otherwise.

A more interesting question would be: Did they lay soft-shelled eggs like crocodiles and pterosaurs or hard-shelled eggs like birds?

in short, as far as we know, there's nothing definitive about live birth in dinosaurs. the possibility of it evolving is kinda dependent upon whether or not the eggs are soft-shelled or hard-shelled

 

[Errnge]

The reason they died out is because they didn't burrow like the mammals.

Though eggs vs live birth is an important point.

i thought it had to due with a meteor hitting earth the size of mt. everest and dinos (by and large, recent finds suggest a few species lived a couple million years after) happened to be too big to survive climate change. not to mention that nothing would survive the impact itself within a certain radius.

and eggs vs live birth isn't that important because we have birds who lay eggs. we even have mammals who lay eggs. it had more to do with size. the smaller an animal is, it tends to be more adaptable and more likely to survive catastrophic events.

we gotta remember, dinosaurs weren't the only things that died out. you have land dwelling crocs, mosasaurs, pterasaurs (though they probably would have in the long run have been driven to extinction by avians), and a myriad of aquatic reptiles.

my bet is that if a meteor hit us right now, same spot and everything, the large animals would be gone first. whales, elephants, bears and big cats, most deer, most dogs, apes, large ungulates, and the likes. you know who would succeed them and us? my bet, birds and rodents.

 

[whitecrow]

Possible, but there are suggestions about that some mammals already had superior brain power ounce-per-ounce. Plus there's the issue that these tiny, apparently flexible, warm-blooded, and insulated creatures died out in the K-T, while mammals did not. There has to be a reason for it.

What I suspect is that it's the egg-laying issue. Live birth is more flexible and (usually) allows a faster birthrate. That is a powerful feature, evolutionarily speaking.

Did mammals give live birth at that point? I thought they were all still monotremes back then.

 

[Sovereign12]

Did mammals give live birth at that point? I thought they were all still monotremes back then.

No marsupials and placentals were both around already.

 

[Zuvarq]

Really? How did they work that out, I wonder? One would thing that burrowing is a capability pretty widely available....

Running around eating dragonflies was their lifestyle.

i thought it had to due with a meteor hitting earth the size of mt. everest and dinos (by and large, recent finds suggest a few species lived a couple million years after) happened to be too big to survive climate change. not to mention that nothing would survive the impact itself within a certain radius.

and eggs vs live birth isn't that important because we have birds who lay eggs. we even have mammals who lay eggs. it had more to do with size. the smaller an animal is, it tends to be more adaptable and more likely to survive catastrophic events.

we gotta remember, dinosaurs weren't the only things that died out. you have land dwelling crocs, mosasaurs, pterasaurs (though they probably would have in the long run have been driven to extinction by avians), and a myriad of aquatic reptiles.

my bet is that if a meteor hit us right now, same spot and everything, the large animals would be gone first. whales, elephants, bears and big cats, most deer, most dogs, apes, large ungulates, and the likes. you know who would succeed them and us? my bet, birds and rodents.

Being able to burrow allows an organism to cope with something like that. If you're out in the open, and 90% of creatures and 99% of plants have died, you'll starve. If you can burrow and hibernate and eat roots and stuff, you have at least a little bit of a chance to survive until the disaster clears.

We were discussing tiny feathered-but-not-bird dinosaurs. Not all dinosaurs. Size doesn't apply in this case--many of them were roughly cat-sized, and plenty of mammals that were as large as cats survived K-T.

Oh I know.
Though there wasn't really a 'myriad' of aquatic reptiles in the late Cretaceous, there were a few mosasaur species, a few plesiosaur species, and the ichthyosaurs and others had died out.

I agree.

 

[Snake Featherston]

Based off of some theories mammals would be dominant, but there would likely still be dinosaurs in the T rex role, and probably the sauropod role too.

Why, necessarily? Mammals appeared at the same time the first dinosaurs did but didn't take over in the late Triassic. No K-T extinction doesn't open the niches for mammals that led them to do so IOTL.

I think the idea of dinosaurs continuing to dominate the earth is rather optimistic in my opinion, omnivores still have a massive natural advantage. Of course humans almost certainly won't exist, not our version anyway, but warm blooded mammals would still be dominant by the present day.

Well, mammals appeared at the same time in the late Triassic that the dinosaurs started doing so in large numbers. Yet dinosaurs went on to dominate megafauna and displace pterosaurs in the air for the next 150 million years. What's going to suddenly change that in favor of the mammals here? Obviously the Cretaceous behemoths won't make it to 2011, but then the Maastrichian theropods weren't simply souped-up Allosaurs, either.

I think that mammals and birds (or bird-formed dinosaurs, if you will) will edge out dinosaurs eventually, but this will be over a period of many millions of years (and possibly would not be complete by our time). However, every major catastrophe and extinction that destroyed dominant mammal species in OTL will instead destroy major dinosaur and reptilian species, opening up their niches for exploitation by lesser dinosaur, avian, and mammal species. Pterosaurs will be edged out by birds, while Mosasaurs and other marine reptiles will be edged out by mammals, birds, and/or dinosaurs as the oceans cool. Even if Mosasaurs survive in warm areas, marine mammals and birds will be able to survive and even thrive in both cold and warm areas, a flexibility that guarantees their eventual inheritance of the oceans.

On land, you might get something like the following: Sauropods go extinct, and are replaced by hadrosaurs who develop body shapes very similar to that of the previous sauropods. Eventually, the long-necked hadrosaurs will go extinct in turn, and their position as the dominant herbivores will be usurped by mammals or whatever new groups of herbivorous mammals have evolved.

Now this makes *some* sense except that over 150 million years there were faunal turnovers in the dinosaur era repeatedly. The tetaneurans replaced the older theropods, the Tyrannosaurs were already displacing the Allosauroids and could easily have done so to the Abelisaurids if they'd ever gotten into South America. Dinosaurs adapted to the rise of flowering plants with the disappearance of sauropods and a dramatic increase in the ornithiscians. They *did* evolve and had every reason to adapt further to the rise of flowering plants, which could easily in fact have increased the number of dinosaurs on the planet due to there being a lot more food for them to eat.

Possible, but there are suggestions about that some mammals already had superior brain power ounce-per-ounce. Plus there's the issue that these tiny, apparently flexible, warm-blooded, and insulated creatures died out in the K-T, while mammals did not. There has to be a reason for it.

What I suspect is that it's the egg-laying issue. Live birth is more flexible and (usually) allows a faster birthrate. That is a powerful feature, evolutionarily speaking.

Yet if we consider that mammals already existed in the Late Triassic and any changes here would be slow and gradual.....mammals won't dominate the planet, but the planet would also be unlikely to have any single predominant group of megafauna. Dinosaurs might end up eating lower-quality plant food where large mammalian herbivores could in some ways fill the niches sauropds left vacant (can anyone say http://en.wikipedia.org/wiki/Paraceratherium) leading to an interesting fauna where dinosaurs fill the niches antelopes and pronghorns do, while things like *that* fill sauropod niches......

The reason they died out is because they didn't burrow like the mammals.

Though eggs vs live birth is an important point.

Which is why birds, crocodilians, and turtles all went extinct 65,000,000 years ago too, eh?

 

[Snake Featherston]

Did mammals give live birth at that point? I thought they were all still monotremes back then.

Actually primates already existed in the Maastrichian (that would be the Cretaceous up to the K-T boundary).

 

[Zuvarq]

Which is why birds, crocodilians, and turtles all went extinct 65,000,000 years ago too, eh?

The tiny insect-eating or egg-stealing theropods of the late Cretaceous all had feathers and were warmblooded. There two main differences between them and the mammals of the time--they did not burrow, and they laid eggs. There has to be some reason why they went extinct and mammals didn't.

 

[Snake Featherston]

The tiny insect-eating or egg-stealing theropods of the late Cretaceous all had feathers and were warmblooded. There two main differences between them and the mammals of the time--they did not burrow, and they laid eggs. There has to be some reason why they went extinct and mammals didn't.

Perhaps that had to do with the extinction of dinosaurian megafauna removing the niches they'd fit into, which may have been over-specialized? We know less about that sort of thing with dinosaurian fauna but I'd not be surprised if by the late Cretaceous at least some dinosaurs were as specialized as today's coconut crabs and equally vulnerable.

 

[oshron]

in natural mass extinctions, its always the big animals that go first. most recently, it was mammoths, terror birds, sloths, woolly rhinos, and the like. today, its elephants and tigers and such animals that are in danger. granted, these animals are being driven to extinction by mankind, but i believe the point is valid

EDIT: another reply from a friend. he was responding to the question of hard- or soft-shelled eggs in dinosaurs:

Hard-shelled eggs for all dinosaur eggs that have been found yet.

 

[Admiral Matt]

i thought it had to due with a meteor hitting earth the size of mt. everest and dinos (by and large, recent finds suggest a few species lived a couple million years after) happened to be too big to survive climate change. not to mention that nothing would survive the impact itself within a certain radius.

and eggs vs live birth isn't that important because we have birds who lay eggs. we even have mammals who lay eggs. it had more to do with size. the smaller an animal is, it tends to be more adaptable and more likely to survive catastrophic events.

we gotta remember, dinosaurs weren't the only things that died out. you have land dwelling crocs, mosasaurs, pterasaurs (though they probably would have in the long run have been driven to extinction by avians), and a myriad of aquatic reptiles.

my bet is that if a meteor hit us right now, same spot and everything, the large animals would be gone first. whales, elephants, bears and big cats, most deer, most dogs, apes, large ungulates, and the likes. you know who would succeed them and us? my bet, birds and rodents.

All well and good, except we were specifically speaking of small dinosaurs, down to the size of a red squirrel. If size were the only consideration, they'd be all over the place. Instead, they died off at the same time as did their larger cousins.

Similarly, for the cephalopods the event was a holocaust. This despite the fact that they tended to be quite small - many significantly smaller than fish genera who did just fine out of the event.

 

[Zuvarq]

All well and good, except we were specifically speaking of small dinosaurs, down to the size of a red squirrel. If size were the only consideration, they'd be all over the place. Instead, they died off at the same time as did their larger cousins.

Similarly, for the cephalopods the event was a holocaust. This despite the fact that they tended to be quite small - many significantly smaller than fish genera who did just fine out of the event.

I think natural history selects against badassery.

Case in point: sea scorpions, crocodile-sized amphibians, those really ancient ferns that looked all alien and mushroomy and crap but were the size of the largest trees today, postosuchus, pterosaurs, ichthyosaurs, mosasaurs, small fast dinosaurs, tyrannosaurs, the dinosaurs as a whole, terror birds, basilosaurus, mammoths, and, lastly, the fact that cuttlefish and octopae are not the undisputed masters of the world.

 

[Admiral Matt]

Why, necessarily? Mammals appeared at the same time the first dinosaurs did but didn't take over in the late Triassic. No K-T extinction doesn't open the niches for mammals that led them to do so IOTL.

Out and out dominant is questionable, but I think they have a good chance of becoming the dominant herbivores in North America and Eurasia. The ice ages would be a disaster for dinosauria in those regions. The only things that could compete effectively would be the theropods, and they have the problem that they're predominately specialized as strict carnivores. That means that while they can certainly survive in the region, it's likely to be mostly in roles preying on birds and mammals. Only the ornithomimosaurs were both feathered and herbivorous, and they had the aforementioned problem of being on the big side needing to develop smaller forms, whereas the mammals and birds can move more easily in the opposite direction whenever the opportunity arises.

Further, there's a limit to grazing ability in bipeds and lipless organisms. That's why mammals dominate the field and the herbivorous birds mostly eat fruit and seeds - the easy things to do with bills. Not that ornithomimosaurs couldn't go quadripedal. I think some forms probably would. But they have to make that transition, which takes evolutionary time. The mammals have real advantages.

 

[oshron]

All well and good, except we were specifically speaking of small dinosaurs, down to the size of a red squirrel. If size were the only consideration, they'd be all over the place. Instead, they died off at the same time as did their larger cousins.

well actually, most dinosaurs around that size are dinosaurs are what we would call birds. thats why, nowadays, the KT extinction is called the mass extinction of NON-AVIAN dinosaurs, and not JUST dinosaurs. it should be noted, though, that the placement of birds among dinosaurs is a bit uncertain.

while on the matter of birds, the probability of them driving pterosaurs to extinction is pretty low, methinks. some pterosaurs, yeah, but not all of them. more likely, some pterosaurs will die out in other ways and some groups of birds will evolve to take their place. for example, the niche of the extinct pteranodonts that are mentioned in the timeline i posted would be taken over by some kind of birds. maybe albatrosses?

besides, theres plenty of niches that birds can take over that pterosaurs arent exploiting. besides, pterosaurs cant swim like birds can, and flightless birds are already present in plenty of environments, so why not ITTL?

 

[Snake Featherston]

Out and out dominant is questionable, but I think they have a good chance of becoming the dominant herbivores in North America and Eurasia. The ice ages would be a disaster for dinosauria in those regions. The only things that could compete effectively would be the theropods, and they have the problem that they're predominately specialized as strict carnivores. That means that while they can certainly survive in the region, it's likely to be mostly in roles preying on birds and mammals. Only the ornithomimosaurs were both feathered and herbivorous, and they had the aforementioned problem of being on the big side needing to develop smaller forms, whereas the mammals and birds can move more easily in the opposite direction whenever the opportunity arises.

Further, there's a limit to grazing ability in bipeds and lipless organisms. That's why mammals dominate the field and the herbivorous birds mostly eat fruit and seeds - the easy things to do with bills. Not that ornithomimosaurs couldn't go quadripedal. I think some forms probably would. But they have to make that transition, which takes evolutionary time. The mammals have real advantages.

And I agree with this. That's why I said that there'd actually be a more diverse fauna than IOTL here. Avian theropods have produced several times megafaunal predators, of which the Phorusacids were a later example but not atypical of Cenozoic dinosaurs (interestingly if you see it in a cladistic light pre-Maori New Zealand was the last dinosaurian ecosystem on the planet with Moae as hadrosaurs and Haast's eagles as avian theropods).

And again, while this is so there have been bipedal herbivorous megafauna even into the historical era, the elephant birds, moae, and dodo are all examples of this.

I think natural history selects against badassery.

Case in point: sea scorpions, crocodile-sized amphibians, those really ancient ferns that looked all alien and mushroomy and crap but were the size of the largest trees today, postosuchus, pterosaurs, ichthyosaurs, mosasaurs, small fast dinosaurs, tyrannosaurs, the dinosaurs as a whole, terror birds, basilosaurus, mammoths, and, lastly, the fact that cuttlefish and octopae are not the undisputed masters of the world.

Except that the temnospondyls actually lasted into the Cretaceous, while a relict population of Woolly Mammoths lasted into the days of Ancient Egypt and Ancient Assyria......

 

[Zuvarq]

Except that the temnospondyls actually lasted into the Cretaceous, while a relict population of Woolly Mammoths lasted into the days of Ancient Egypt and Ancient Assyria......

I was talking about natural history as a whole, not natural history before the K-T event. And note I said natural history, not survival of the fittest or natural selection, because K-T killed a lot of the animals on my list.