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goingtothedo

Why did birds, of all the dinosaurs, survive the KT event?

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A bit of speculation of my own. If anyone can contribute with evidence or relevant information I'd love to hear it.

 

 

 

Many now accept that the great extinction at the KT boundary was probably caused by an asteroid hit. One of the puzzles regarding that extinction is the selection of animal species, specifically dinosaur species surviving the catastrophe. We still have the birds with us, but in different forms to the archaic birds, and the non-avian dinosaurs are gone.

 

Has anyone suggested the following? Or, can you suggest a book or other reading?

 

Birds now largely have one of two mechanisms for attracting a mate; either gaudy plumage which they may display in some kind of dance, or singing. Not many use both. Off-hand I can only think of lyre birds.

 

By extension, it seems reasonable to think that the dinosaurs may have had similar behaviours and we know now that feathers were common among the dinosaurs. We also know that the feathers came in degrees; from a few plumaceous wisps to a full body covering.

 

The lucky survivors of the KT strike also needed to be lucky reproducers for their line make it through to the present. Could these lucky few have been the ones with a combination of (a) A full set of feathers (b) The habit of attracting a mate by singing?

 

A full set of feathers would be an aid to survival simply in the sense of being “body armour”. And even feathers badly damaged in the strike and its immediate aftermath (heat, blast, atmospheric fallout, sulphuric acid rain etc) will regrow at the next moult if their owner has not been too badly damaged.

 

Feathers as insulators would also be hugely useful is the medium term as an aid to survival against the cold darkness of the “nuclear winter” following the strike.

 

However, in the darkness, which was deep enough to kill most of the plant life, a bird who tried to attract his mate with a plumage display would have severe problems. His prospective partners would not be able to see (and presumably admire) his plumage.

 

A bird who sang on the other hand, would be able to find his mate even in the darkness.

 

So, could the deciding factor in who survived the extinction lottery of the KT strike be

 

(1) A full set of feathers that would aid immediate survival

 

And

 

(2) Singing as the mate attracting mechanism

 

This has probably been suggested elsewhere, but I would like to read more developed explanations if anyone can tell me where to look.

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If the bolide impact theory is to believed, the subsequent 'nuclear winter' would have 'killed' most of the plants, all the large herbivores, and all the large meat-eaters.

 

Smaller dinosaurs may have survived on seeds and carcasses, but may have been partially warm blooded, so required both higher levels of food than true reptiles as well as sunshine.

 

The reptiles survived because they do not require much food (being cold blooded) AND can go into torpor for long periods.

 

The birds survived because thry are completely warm-blooded, and insulated with feathers, and highly mobile, and small (so could survive on seeds, carrion, etc).

 

The dinosaurs, being neither truly warm-blooded or truly cold-blooded, died out.

 

That's my guess...

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I would put it down to half dumb-luck and half high reproductive capacity. Smaller animals tend to breed faster and this gives them an edge when you have a rapidly and radically changing environment. The population can survive hits well and still maintain enough genetic diversity to adapt.

 

When ever you have lots of change, it's called an r-selective regime, and whenever you have a more stable environment with more competition it's called K-selective, in case you're interested.

"r" refers to the reproductive capacity of a species while "K" refers to the carrying capacity of the environment.

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I tend to favor Bombus' answer. I think it would be a matter of the amount of food needed per animal combined with ability to withstand the cold of the winter. Mammals, turtles, and some reptiles burrow, thus insulating themselves against the winter. The feathered dinos were 1) larger and 2) carnivores. So they were more susceptible to the cold and their food supply died.

 

As Bombus noted, many birds eat seeds or carrion. Even if the plants died, the seeds would still be available. The smaller birds would not need so much food and would have less body area to lose heat.

 

Remember that several genera of birds also went extinct at the K-T boundary. BTW, birds are descended from dinos, but the class Aves was well established by the time the K-T event occurred.

 

I have not seen a paper discussing the reasons the birds survived. Not surprising, since there is still debate as to the exact reason the dinos went extinct. Data indicates that the number of dino species was in a steep decline for at least 10 million years prior to the meteor impact. Robert Bakker, for one, doesn't think the meteor was the primary cause of dino extinction, but merely provided the icing on the cake. His position is controversial, but respected.

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The dinosaurs, being neither truly warm-blooded or truly cold-blooded, died out.

 

I have a bit of trouble with this, for a couple of reasons:

1. I'm not sure some dinos were not completely warm-blooded.

2. Dinos thrived in Antarctica when it was at the south pole. True, it was warmer than today so that it was more like the Arctic (with warm summers), but apparently still went thru some pretty cold winters.

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Robert Bakker, for one, doesn't think the meteor was the primary cause of dino extinction, but merely provided the icing on the cake. His position is controversial, but respected.

 

Professor Michael Boulter says the same thing. His research suggests it's all down to 'self organized criticality'. I think he might very well be right.

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The smaller birds would not need so much food and would have less body area to lose heat.

 

Er... wrong reasoning here, lucaspa.

 

It is just the opposite. What really matters for the conservation of body temperature is the quotient between body volume and body area. The bigger the quotient is the bigger the conservation of temperature is. And this quotient increases with body size because volume increases faster than area.

 

What protected birds from winter was mainly their coat of feathers. After that, it was, probably, their capacity to shelter themselves inside burrows and their warm-bloodiness.

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The short answer is that we do not know. We can speculate all we like, but more data is needed. In the last 10 years, we have discovered an amazing amount of information about dinosaurs. It is predictable that we will discover a heap more in the next 20 years about all forms of life before and after the big disaster.

 

Watch this space....

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Professor Michael Boulter says the same thing. His research suggests it's all down to 'self organized criticality'. I think he might very well be right.

 

This paper says SOC may be correlated with the origin of species, but not in extinction: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1690677

 

I really can't see how SOC can be "down to" as in the answer to everything within evolutionary biology. Nor can it explain the gradual decline in dino species: they already WERE "organized" as organisms.

 

FYI, here is a rather scathing review of Boulter's book: http://palaeo-electronica.org/2003_2/books/extinc.htm

 

It's plain from deep sea cores that the KT impact did wipe out many species, especially plankton. Destruction of that many species certainly disrupted the ecosystem and that, in turn, caused the extinction of other species.

 

The argument is whether dinos were in decline and would have gone extinct without the KT event. That is very dicey and, ultimately, untestable. Since the meteor DID hit, how can you test an alternate future that never happened? All I can do is note that there was a decline in the number of species and a "minor" extinction event at the end of the Triassic. The suborder Dinosauria came thru that and then re-diversified in the Cretaceous. An alternative hypothesis is that this pattern would have repeated. Again, it too is untestable for the same reasons.

 

It's a fun argument, but since we can never get the data to settle it, I refuse to get too serious about the argument.

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Er... wrong reasoning here, lucaspa.

 

It is just the opposite. What really matters for the conservation of body temperature is the quotient between body volume and body area. The bigger the quotient is the bigger the conservation of temperature is. And this quotient increases with body size because volume increases faster than area.

 

What protected birds from winter was mainly their coat of feathers. After that, it was, probably, their capacity to shelter themselves inside burrows and their warm-bloodiness.

 

I understand the relation of body size and volume. However, this only works in a general sense, not in terms of keeping heat in a very cold environment. The larger the area, the more heat is lost. Period. If it is VERY cold relative to body temperature, then this comes into play: you are losing more heat than you can replace by metabolism. If you are smaller, the amount of heat lost is smaller, therefore the less you have to replace by metabolism. Think of mammals that live in the arctic. Yes, you do have larger mammals, but they still needed to evolve longer fur. Their increased body size isn't enough to provide the necessary heat balance. And we are talking an event that happened overnight, so no time to evolve better insulation. In that situation, smaller animals have an advantage.

 

I was thinking about the insulation of feathers and how small birds stick around in winters. They are even able to be covered by snow because the snow itself then acts as additional insulation -- see igloos.

 

So, small birds with insulation, lower rate of heat loss, and reduced food requirements (because of their small size) are going to be able to survive the impact winter better than larger animals with our without insulation.

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lucaspa said :

 

If you are smaller, the amount of heat lost is smaller, therefore the less you have to replace by metabolism

 

Actually the reverse is correct. Proportional to body mass, the larger an animal is, the less the heat loss. That is why an elephant has almost no hair and has developed those massive ears, which it flaps around to lose heat. Whales have no hair either, and maintain body heat without external insulation in the Earth's coldest oceans. Admittedly, they have blubber layers, but these are less efficient insulators than air held under hair or feathers.

 

Small animals have to eat enormous amounts of food to replace the energy lost as heat. A shrew will eat half its body mass each day.

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Small animals have to eat enormous amounts of food to replace the energy lost as heat. A shrew will eat half its body mass each day.

 

I suspect Lucaspa's point is that it's easier in famine times to fuel half a shrew than it is to fuel a 5-tonne monster.

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This paper says SOC may be correlated with the origin of species, but not in extinction: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1690677

 

I really can't see how SOC can be "down to" as in the answer to everything within evolutionary biology. Nor can it explain the gradual decline in dino species: they already WERE "organized" as organisms.

 

I don't get what you're trying to say? All the SOC 'theory' is saying is that evolution, radiation and extinction follow power law principles, like just about everything else. That would make sense to me.

 

FYI, here is a rather scathing review of Boulter's book: http://palaeo-electronica.org/2003_2/books/extinc.htm

 

It's plain from deep sea cores that the KT impact did wipe out many species, especially plankton. Destruction of that many species certainly disrupted the ecosystem and that, in turn, caused the extinction of other species.

 

The argument is whether dinos were in decline and would have gone extinct without the KT event. That is very dicey and, ultimately, untestable. Since the meteor DID hit, how can you test an alternate future that never happened? All I can do is note that there was a decline in the number of species and a "minor" extinction event at the end of the Triassic. The suborder Dinosauria came thru that and then re-diversified in the Cretaceous. An alternative hypothesis is that this pattern would have repeated. Again, it too is untestable for the same reasons.

 

It's a fun argument, but since we can never get the data to settle it, I refuse to get too serious about the argument.

 

That's possibly the poorest, most inaccurate, twisted and plain unfair review of a book I have ever read! I reckon she's just envious because she didn't think of it. Half the things she complains about are due to her lack of understanding of what is actually being said. I felt quite upset reading it! What vitriol!

 

Unlike her, Professor Boulter is one of the most prominent and well respected Palobiologists there is.

 

Also, he doesn't dispute that a bolide hit the Earth at all, he justs suggests it was a final nail the coffin.

 

It's actually a great book, and well worth reading.

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how close to being like a modern bird is the most bird like dinosaur that they found so far from before KT? I know some dinosaurs had feathers but i thought they were all still pretty big. i'm guessing they could fly.. because you guys make a good point that feathers insulate well, you think feathers evolved as insulation or as flying tools? did the feathery dinosaurs come from where it was winter sometimes? I know they pretty recently found gigantoraptor http://news.nationalgeographic.com/news/2007/06/070613-giant-dinosaur.html but they think that it only had feathers on the arms and tail... i guess then they must be used more for flying than for warmth. but could such a huge thing really fly?

 

is it possible that there was some limited areas where pretty much all the animals could have survived, but many species didn't live there and couldn't make it there so they all died out? (they probably didn't even know to look for it even when conditions for them got really bad) but flying animals could cover more ground more quickly and are programmed to migrate when temperature changes (at least i think they only base it on temperature). but still birds can live through a winter no sweat, some of them anyways.

 

or did they find pre KT fossils and post KT fossils in the "same" earth?

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I suspect that feathers first evolved for insulation. After all, they came from scales, and an object half way evolved between scale and feather has no value for flight, but may be better than scales alone for insulation.

 

Of course, once evolved, they may have developed all sorts of uses, in addition to insulation and flight. Sexual signals, bright colours, fluffing out as threat displays, shock absorbers etc.

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It has been my understanding that whilst it was once accepted from the fossil record that the dinosaurs had a long slow demise, based on reducing numbers of fossils approaching the KT boundary, that this is no longer accepted.

 

I have read, in several places, that this is now taken to be a statistical artifact, based on the fact that if looking for a specific species, the odds are very high that you will never find "the last one". This produces a tail-off in the fossil record that looks like a gradual dying out of species but is actually what would be statistically expected to be seen for an actual sudden/catastrophic killing off of species

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Actually the reverse is correct. Proportional to body mass, the larger an animal is, the less the heat loss. That is why an elephant has almost no hair and has developed those massive ears, which it flaps around to lose heat.

 

Sayonara made the point for me. Also consider: the elephant is already in a warm climate! What happens if you plunk that elephant down in a blizzard? The large area + no insulation means freezing to death. Now plunk a chickadee down in a blizzard. Smaller area for heat loss, insulation, AND it can get covered up with snow that also acts as insulation. Again, think igloos.

 

Small animals have to eat enormous amounts of food to replace the energy lost as heat. A shrew will eat half its body mass each day.

 

But the body mass is so small! So, on an absolute scale, a shrew has to eat 5 gm per day. How much for an elephant? Several thousand times as much.

 

 

I don't get what you're trying to say? All the SOC 'theory' is saying is that evolution, radiation and extinction follow power law principles, like just about everything else. That would make sense to me.

 

SOC says more than that. It appears you are trying to change SOC to avoid falsification.

 

That's possibly the poorest, most inaccurate, twisted and plain unfair review of a book I have ever read! I reckon she's just envious because she didn't think of it. Half the things she complains about are due to her lack of understanding of what is actually being said. I felt quite upset reading it! What vitriol!

 

Quite a bit of vitriol in your comments, too. Are you sure it is her misunderstandig and not yours? After all, she is a paleontologist.

 

Unlike her, Professor Boulter is one of the most prominent and well respected Palobiologists there is.

 

Again, more ad hominem. The reviewer is quite prominent also. Did you read her bio? But, of course, the question isn't Boulter's standing, but the ideas. Ironically,the reviewer comments that Boulter spends most of the book using ad hominem on other people. Is that true?

 

It's actually a great book, and well worth reading.

 

I understand it's your opinion. I was just pointing out that your view is not universal.

 

 

how close to being like a modern bird is the most bird like dinosaur that they found so far from before KT? I know some dinosaurs had feathers but i thought they were all still pretty big. i'm guessing they could fly.. because you guys make a good point that feathers insulate well, you think feathers evolved as insulation or as flying tools?

 

1.There are species that are essentially modern birds from before the KT. As I said, birds had already diverged from dinos before the KT boundary.

C Zimmer, A sickle in the clouds. Discover 19: 32, June 1998. New bird, primitive like Archy, 65-70 MYa, found in Madagascar. Has sickle claw like Velociraptor. Named Rahonavis ostrami. Primary article is: Forster, C A, Sampson, S D, Chiappe, L M, and Krause, D W. 1998. The theropod ancestory of birds: new evidence from the Late Cretaceous of Madagascar. Science 279:1915-1919.

L Chiappe, Wings over Spain. Natural History 107: 30-32, Sept. 1998. Describes primitive birds from 115 Mya. KT was 65 million years ago.

 

2. Archeopteryx is a very bird-like dinosaur. :) But there is also this one: E Stokstad, Tiny, feathered dino is most birdlike yet. Science 290: 1871-1872, Dec. 2000.

 

3. Large feathered dinos could not fly. It appears that feathers first evolved for display -- sexual display. Feathers were later exapted for insulation and then exapted again for flight. There is a continuum of how much of the dinos were covered by feathers. There are fossils of dinos with only 1 or 2 feathers and then fossils where the entire animal is covered.

 

Here, this is probably a good article for you:

Kevin Padian When is a bird not a bird? Nature 393, 729; 1998

http://www.nature.com/Nature2/serve?SID=25602728&CAT=NatGen&PG=dino/dino2.html

Here are some more:

M Nowell, First came feathers. Natural History 107: 33, Sept. 1998. Summary of recent discoveries in China. Sinosauropteryx did not have true feathers; intermediates between scales and feathers.

T Appenzeller, T. Rex was firece, yes, but feathered, too. Science 285: 2052-2053, Sept. 24, 1999. Discovery of down on dromeosaurs. "partial" feathers.

http://research.amnh.org/vertpaleo/dinobird.html

P J Currie et al., Two feathered dinosaurs from northeastern China, Nature 393, 753; 1998. (June 25). Reports summarized in A Gibbons, Dinosaur fossils, in fine feather, show link to birds. Science 280: 2051 (26 June) 1998.

 

is it possible that there was some limited areas where pretty much all the animals could have survived, but many species didn't live there and couldn't make it there so they all died out?

 

Theoretically possible, but the data says "no". Dinos were distributed thruout the globe. So if there had been an area were they survived, then we would have dinos today. Also, dino fossils stop VERY abruptly at the KT boundary. Many species of birds also disappear at the KT boundary. The enantiornithines (the dominant Cretaceous bird group of which Confuciousornis is a member) went extinct and only the neornithines made it through. In addition, the hesperornithoformes and the icthyornithoformes (the toothed seabirds) went extinct at the end of the Cretaceous.

 

 

It has been my understanding that whilst it was once accepted from the fossil record that the dinosaurs had a long slow demise, based on reducing numbers of fossils approaching the KT boundary, that this is no longer accepted.

 

I have read, in several places, that this is now taken to be a statistical artifact, based on the fact that if looking for a specific species, the odds are very high that you will never find "the last one". This produces a tail-off in the fossil record that looks like a gradual dying out of species but is actually what would be statistically expected to be seen for an actual sudden/catastrophic killing off of species

 

:confused: That last sentence makes no sense. Why would you have a "tailing off" for 10 million years before the meteor hit? If it was a catastrophic kill on a robust lineage, you should see the same populations up until the moment the meteor hits.

 

So, can you please point us to your sources? We seem to have contradictory data -- decline in numbers of individuals and species before the KT implact and no decline. We need to look at the original papers to resolve this.

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lucaspa said :

 

Also consider: the elephant is already in a warm climate! What happens if you plunk that elephant down in a blizzard? The large area + no insulation means freezing to death.

 

Not a good example, since modern elephants are adapted to living in the tropics. That's why they got big ears! However, we have the example of the woolly mammoth, adapted to very cold conditions.

 

Even more dramatic, though, are mammals adapted to living in the sea. Heat loss, for a specific thermal gradient, is about 30 times as rapid for an animal immersed in water compared to one in air. Thus, animals in cold Arctic or Antarctic waters need to have a means of conserving heat. While this can be achieved by fur or feathers that retain a film of air underwater, or a thick layer of blubber, the best method of conserving heat in frigid aquatic environments is simply size. Seals and penguins often have to get out of the water to warm up. Very large marine mammals (whales and sea elephants) can stay in water at minus 2 Celsius for months or years at a time.

 

When they move into warmer waters, their big problem is over-heating. Humpback whales have enormous pectorals, into which they can pump lots of blood to provide a cooling surface, when in warm waters. Other whales have alternative cooling methods, such as pumping more blood into skin in the tail flukes.

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SOC says more than that. It appears you are trying to change SOC to avoid falsification.

 

Like what?

 

Quite a bit of vitriol in your comments, too. Are you sure it is her misunderstandig and not yours? After all, she is a paleontologist.

 

But well deserved ;) The review has taken many things out of context and in many cases she just seems to have completely misunderstood what is actually being said, to the point of thinking M. Boulter is saying the opposite of what he is actually saying. She also misunderstands the tone of the book, taking offence when none is intended, and some of her statements just show how she doesn't undertand the 'big concept' at all.

 

Again, more ad hominem. The reviewer is quite prominent also. Did you read her bio? But, of course, the question isn't Boulter's standing, but the ideas. Ironically,the reviewer comments that Boulter spends most of the book using ad hominem on other people. Is that true?

 

Well she is an Associate Professor, which isn't a real professor at all. M. Boulter has been the Secretary of the International Organisation of Paleobiology for over twenty years. He is also the Chair the UK Governments Biodiversity Steering group. Having met him on numerous occasions, I know him to be a modest, honest and very (very!) clever scientist, not the unscholarly, boastful, anti US data-thief Ms. Walker seems to portray. I'm sure if she met him she'd feel quite ashamed!

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Oh, that makes sense. What are the common attributes of the creatures that ended up dying because of KT? Is there some sort of website you know of that shows images of most creatures that died and most that survived?

 

What materials were found in the layer of earth that makes KT visible?

 

what was the earth shaped like in that period?

 

I guess it's probably impossible or very difficult to accurately know what the climate was in all areas of the earth in those days since the climate is not strictly influenced by latitude, but has anyone ever constructed a climate model for that period?

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lucaspa said :

 

Also consider: the elephant is already in a warm climate! What happens if you plunk that elephant down in a blizzard? The large area + no insulation means freezing to death.

 

Not a good example, since modern elephants are adapted to living in the tropics. That's why they got big ears! However, we have the example of the woolly mammoth, adapted to very cold conditions.

 

Even more dramatic, though, are mammals adapted to living in the sea. Heat loss, for a specific thermal gradient, is about 30 times as rapid for an animal immersed in water compared to one in air. Thus, animals in cold Arctic or Antarctic waters need to have a means of conserving heat. While this can be achieved by fur or feathers that retain a film of air underwater, or a thick layer of blubber, the best method of conserving heat in frigid aquatic environments is simply size. Seals and penguins often have to get out of the water to warm up. Very large marine mammals (whales and sea elephants) can stay in water at minus 2 Celsius for months or years at a time.

 

When they move into warmer waters, their big problem is over-heating. Humpback whales have enormous pectorals, into which they can pump lots of blood to provide a cooling surface, when in warm waters. Other whales have alternative cooling methods, such as pumping more blood into skin in the tail flukes.

 

SkepticLance , I was about to post similar arguments. Thank you for saving me the effort. :)

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lucaspa said :

 

Also consider: the elephant is already in a warm climate! What happens if you plunk that elephant down in a blizzard? The large area + no insulation means freezing to death.

 

Not a good example, since modern elephants are adapted to living in the tropics. That's why they got big ears! However, we have the example of the woolly mammoth, adapted to very cold conditions.

 

But the point is that, in the nuclear winter following the meteor impact of the KT boundary, all life adapted to living in the warm Cretaceous would have been immediately -- in a single day -- been subjected to a blizzard!

 

You've forgotten the context of what we are talking about. We aren't talking about gradual evolution of a population to a cold climate. We are talking about instantaneous transformation of the climate from warm to cold. As you noted, in this instantaneous transistion, elephants are at an even greater disadvantage because of their ears -- adapted to giving off heat. Now imagine what this does to the poor elephant, adapted to living in the tropics, suddenly having a blizzard. It freezes to death even faster.

 

But the small birds of the savannah -- with their insulation and smaller body area to lose heat -- might live thru the blizzard.

 

And then, of course, is the food problem. You thought I would forget that?

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You've forgotten the context of what we are talking about. We aren't talking about gradual evolution of a population to a cold climate. We are talking about instantaneous transformation of the climate from warm to cold. As you noted, in this instantaneous transistion, elephants are at an even greater disadvantage because of their ears -- adapted to giving off heat. Now imagine what this does to the poor elephant, adapted to living in the tropics, suddenly having a blizzard. It freezes to death even faster.

 

Hannibal used elephants to fight romans. They crossed the cold Andes mountains and survived.

 

But the small birds of the savannah -- with their insulation and smaller body area to lose heat -- might live thru the blizzard.

 

I find mind boggling that you still do not understand that big bodies have smaller surface in relation to their volume and therefore conserve temperature better.

 

Small birds and small mammalians survived simply because they could protect themselves against cold by hiding inside burrows and require far less food to survive. If they had no feathers or fur ( plus burrows ) to compensate for small body size they would die first.

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but also things like crocodiles survived, and they aren't particularly small like birds. i think wondering why only birds survived is not necessarily the most helpful thing to finding out why birds survived. perhaps the most helpful thing would be to have basically a list of all creatures that survived and where they lived on a period map. there must be some common characteristics among the creatures that survived, perhaps in ability, or mobility rather than physical characteristics. Birds weren't the only things to survive so strictly size and feathers would perhaps account for the birds but then how come other creatures survived? there may be different reasons why some creatures survived and others not but i would guess it is slightly more likely that all the creatures that survived had a common attribute that allowed for their survival.

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Oh, that makes sense. What are the common attributes of the creatures that ended up dying because of KT? Is there some sort of website you know of that shows images of most creatures that died and most that survived?

 

What materials were found in the layer of earth that makes KT visible?

 

what was the earth shaped like in that period?

 

I guess it's probably impossible or very difficult to accurately know what the climate was in all areas of the earth in those days since the climate is not strictly influenced by latitude, but has anyone ever constructed a climate model for that period?

 

Well some event happened that basically in a uniform fashion managed to "shock" quartz into a specific form all over the planet.

 

As for bird survival, well, they would have been able to move more easily in a terrain where food might have become a bit scarce. That’s just one idea I have as to why they might have persisted, I don’t know any factual reasons.

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