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Ok you Mathamaticians!

  • #21
[b said:
Quote[/b] (Mokele @ July 20 2006,10:32)]
Hey Mokele,

[b said:
Quote[/b] ]Well, the idea is that the cold was a minor second problem, while the big issue was dust choking out the light and impeding photosynthesis. That would mean less plants, which would mean less herbivores, which means less carnivores...

When you hear it discussed it is most always put forth as the mother of all "Nuclear Winter" situations and I think most people feel that way, even the scientists. And yes it would be the double play of the dust cooling and blotting out the sun that would be the cause but I still don't buy it. Look at it this way, if you upset the lowest level of the food web then ALL the upper levels will feel it. KNock out the plants and yes you knock out the herbivores but not just the big one, you lose all the little ones too, like insects. You lose the insects and you lose the food supply for the smaller mammals and herps. You lose the small mammals and herps you lose the food for the larger mamals and herps... Ad infinitum. So again, why did the herps and smaller critters come out less scathed than the dinos??

[b said:
Quote[/b] ]with the big things and the warm-blooded things (since both large size and high metabolism increase food requirements) being the first to starve

Actually that is not fully correct, there is not a linear increas in size and food intake. In fact most smaller warm bloods have to eat more than their own mass to maintain their body heat because their small size means they radiate the heat faster.

[b said:
Quote[/b] ]Also, it's technically inaccurate to say that ectotherms survived unscatched; many species of crocodylians and other reptiles perished, including the pterosaurs and marine reptiles. They just didn't get screwed nearly as badly as the dinosaurs did.

I never said unscathed I said "more or less untouched" which is pretty accurate. Yes, some crocodiliads died off, but not all. Yes the pterosaurs died off however, 1) they were also considered to be warm blooded and 2) I group them in with the dinos as far as the extiction talk goes so they are on that side of the equation for me. As for the marine reptiles, data nowadays seems to indicate that they were dying off long before the meteor hit so while it might have done them in they were already on the way out.

[b said:
Quote[/b] ]There is, of course, still debate. Other alternatives include Bakker's theory, volcanic eruptions, or disease.

Bakker's theory is the disease theory (unless he has come up with something new) and AFAIC the volcano theory is just slant on the meteor theory, lots of ash and smoke...

[b said:
Quote[/b] ]It's complciated by the fact we've never directly witnessed a large asteroid strike on a rocky planet, thus must rely on historical evidence to infer the effects. Hopefully if that situation changes, it'll involve the moon or some rocky planet other than Earth.

I'll agree that it is complicated but I still thenk that people jump to "smoking gun" too soon.
 
  • #22
[b said:
Quote[/b] ]When you hear it discussed it is most always put forth as the mother of all "Nuclear Winter" situations and I think most people feel that way, even the scientists. And yes it would be the double play of the dust cooling and blotting out the sun that would be the cause but I still don't buy it.

Well, first, you must remember that the Alvarez paper (proposing the asteriod impact) was proposed before Bakker's theories of endothermy.

Secondly, we do know that there was a big impact event around the right time, and such events would likely cause a nuclear winter effect. The real question is more whether this is what killed them off or not.

[b said:
Quote[/b] ]Look at it this way, if you upset the lowest level of the food web then ALL the upper levels will feel it. KNock out the plants and yes you knock out the herbivores but not just the big one, you lose all the little ones too, like insects. You lose the insects and you lose the food supply for the smaller mammals and herps. You lose the small mammals and herps you lose the food for the larger mamals and herps... Ad infinitum. So again, why did the herps and smaller critters come out less scathed than the dinos??

Because the producers were not eliminated, just impeded. Some plants, as you no doubt know, can work with low light levels and cool temperatures. This would create an impediment to all subsequent trophic levels, with only those organisms who can manage to fulfill their dietary requirements surviving. Thus the animals with the lowest dietary requirements survive, those with the highest die.

[b said:
Quote[/b] ]Actually that is not fully correct, there is not a linear increas in size and food intake. In fact most smaller warm bloods have to eat more than their own mass to maintain their body heat because their small size means they radiate the heat faster.

I never said it was linear, only that it increases with both size and metabolism. Trust me, I am more than aware of allometry and biological scaling; it's a large part of what I do.

Also, it doesn't matter to my point. Small animals need *proportionally* more food, but not on an absolute scale. A mouse needs more food than a lizard, and an elephant needs more than a mouse. Sure, it's not linear, but all that matters is that big things, warm things, and especially big warm things, need a *LOT* of food.

[b said:
Quote[/b] ]I'll agree that it is complicated but I still thenk that people jump to "smoking gun" too soon

I strongly suspect there's less consensus in the scientific community than the media makes out.

Nevermind, this is paleontlogy, the field that gave us the quote "Consensus is established one funeral at a time". I'm amazed they can reach a consensus on where to have meetings.

Mokele
 
  • #23
The problem with the asteroid hypothesis is that it's a photogenic, high school textbook kind of explanation like saying the US Civil War happened because shots were fired at Fort Sumter or that the Great Depression happened because of Black Thursday.  The world is a complicated place.
 
  • #24
Mokele wrote:
[b said:
Quote[/b] ]Nevermind, this is paleontlogy, the field that gave us the quote "Consensus is established one funeral at a time". I'm amazed they can reach a consensus on where to have meetings.
Hmmmm - how do you really feel??
301.gif
 
  • #25
[b said:
Quote[/b] (jimscott @ July 20 2006,9:53)]Would that have something to do with smaller critters having more time to adapt / evolve than the larger ones?
[b said:
Quote[/b] ]And yes it would be the double play of the dust cooling and blotting out the sun that would be the cause but I still don't buy it. Look at it this way, if you upset the lowest level of the food web then ALL the upper levels will feel it. KNock out the plants and yes you knock out the herbivores but not just the big one, you lose all the little ones too, like insects. You lose the insects and you lose the food supply for the smaller mammals and herps. You lose the small mammals and herps you lose the food for the larger mamals and herps... Ad infinitum. So again, why did the herps and smaller critters come out less scathed than the dinos??

Since we've already gone from math to dinosaurs, I wanted to drag this dead quotes back up.
smile_n_32.gif
'The weather' thing always means something else.

Think what Jim meant was that the 'smaller critters' (e.g. worms, bugs...raccoons) could adapt more easily as they lived more generally. I mean, for example, while the larger creatures (i.e. dinos) were more specialized (i.e. some were strictly carnivorous, eating only one type of meat - fussy is the word). While the smaller critters, they could feed off anything, be it plant or meat, and perhaps a larger range of primary food sources (algae, plankton...) as well. So when 'nuclear winter' hits and a source of food is wiped out, the animals that can switch habitat, diets, would be the survivors.

You guys would have probably discussed this to death already, but thought I'd just throw an interesting point in. Plus, I am in no mood for logic, so excuse me if I appear to be doodling and dozing off.
smile_m_32.gif
 
  • #26
[b said:
Quote[/b] ]The problem with the asteroid hypothesis is that it's a photogenic

Definitely. The view the public has of paleo is pretty off, thanks to the media's presentation of the most photogenic theories. For instance, we have one, and only one, find that *might* support pack hunting by dromaeosaurs ("raptors"), though they might also have been scavenging, while we actually have a fossil of a velociraptor and protoceratops locked in combat (likely a sand dune collapsed on top of them) and it's just one of each. (Also, I heard though the grapevine of a yet-unpublished trackway showing a solitary dromaeosaur.) But the media gets things into their heads, and because it's 'sexy' and sells, they parrot it endlessly.

[b said:
Quote[/b] ]Hmmmm - how do you really feel??

hehehe. I'm just rather cynical, and a fellow student I worked with used to do paleo, so she clued me in on all the metaphorical dirt.

[b said:
Quote[/b] ]Think what Jim meant was that the 'smaller critters' (e.g. worms, bugs...raccoons) could adapt more easily as they lived more generally. I mean, for example, while the larger creatures (i.e. dinos) were more specialized (i.e. some were strictly carnivorous, eating only one type of meat - fussy is the word). While the smaller critters, they could feed off anything, be it plant or meat, and perhaps a larger range of primary food sources (algae, plankton...) as well. So when 'nuclear winter' hits and a source of food is wiped out, the animals that can switch habitat, diets, would be the survivors.

Actually, AFAIK, there's no real tendency for big animals to be either specialists or generalists. Plenty of large animals will eat anything they can stuff in their mouths (wolves, lions, crocodiles, elephants, bison), while others are specialist (anteaters, gharials, cheetahs, sperm whales). Similarly, there are generalist small animals (anoles, rodents, roaches, pond turtles, sparrows) and specialists (hummingbirds, snail-eating-snakes, woodpeckers, etc).

While specialists would be hurt more, I'm not aware of specialists vs generalists being more common at either end of the size range. If anything, I'd think that big animals would be more likely to be generalists, since they can't afford to be picky if they're going to feed that huge body.

Mokele
 
  • #27
[b said:
Quote[/b] ]Well, first, you must remember that the Alvarez paper (proposing the asteriod impact) was proposed before Bakker's theories of endothermy.

Yes, I knew/know that. Does not make much of a difference to me. I mean, if everyone can gladly accept the challenge to the idea of cold blooded dinos then why can they not think to challenge the impact when things start to look a little fishy??

[b said:
Quote[/b] ]Secondly, we do know that there was a big impact event around the right time, and such events would likely cause a nuclear winter effect.  The real question is more whether this is what killed them off or not.

I would not say we know but I grok your point. However, there are a bunch of different ways to both interpret and explain the data and that again brings me to the critisizm of jumping to the "smoking gun" and totally discarding everything else.

[b said:
Quote[/b] ]Because the producers were not eliminated, just impeded. Some plants, as you no doubt know, can work with low light levels and cool temperatures.  This would create an impediment to all subsequent trophic levels, with only those organisms who can manage to fulfill their dietary requirements surviving.  Thus the animals with the lowest dietary requirements survive, those with the highest die.

It still does not jive because there would have been dinos that were just as/more maleable/generalist than the small mammals and herps. We are not talking species or genus level extinction here, a global event like an impact is not going to hit selectivly.

[b said:
Quote[/b] ]I never said it was linear, only that it increases with both size and metabolism.  Trust me, I am more than aware of allometry and biological scaling; it's a large part of what I do.

I offer my apologies for misinterpreting.

[b said:
Quote[/b] ]Also, it doesn't matter to my point.  Small animals need *proportionally* more food, but not on an absolute scale.  A mouse needs more food than a lizard, and an elephant needs more than a mouse.  Sure, it's not linear, but all that matters is that big things, warm things, and especially big warm things, need a *LOT* of food.

But not all dinos were big. And some crocodyliads (that made it through) were quite large. And then there is the scavenger aspect, with all those dead bodies scavengers must have had a ton of food so why didn't T rex (assuming you accept the theory that he was a scavenger [which I am not saying I do or do not, just throwing it out as part of the argument]) make it through?

[b said:
Quote[/b] ]I strongly suspect there's less consensus in the scientific community than the media makes out.

I would concur but even in the literature it is pretty slanted.
 
  • #28
[b said:
Quote[/b] (Mokele @ July 22 2006,3:20)]Actually, AFAIK, there's no real tendency for big animals to be either specialists or generalists. Plenty of large animals will eat anything they can stuff in their mouths (wolves, lions, crocodiles, elephants, bison), while others are specialist (anteaters, gharials, cheetahs, sperm whales). Similarly, there are generalist small animals (anoles, rodents, roaches, pond turtles, sparrows) and specialists (hummingbirds, snail-eating-snakes, woodpeckers, etc).

While specialists would be hurt more, I'm not aware of specialists vs generalists being more common at either end of the size range. If anything, I'd think that big animals would be more likely to be generalists, since they can't afford to be picky if they're going to feed that huge body.

Mokele
True, but if not that, then why do all the small critters survive over the big ones (not that all do, but the large ones always seem to go quickly) when there is a mass extinction?

I doubt that large animals could become generalists, really. Just imagine, a T-rex trying to swallow a roach? C'mon!

Joking...
smile_m_32.gif
 
  • #29
[b said:
Quote[/b] ]I mean, if everyone can gladly accept the challenge to the idea of cold blooded dinos then why can they not think to challenge the impact when things start to look a little fishy??

The fact that there are other theories out there indicates that the impact theory *is* being challenged.

[b said:
Quote[/b] ]I would not say we know but I grok your point. However, there are a bunch of different ways to both interpret and explain the data and that again brings me to the critisizm of jumping to the "smoking gun" and totally discarding everything else.

Well, we do know: we've got a worldwide iridium layer and a giant crater off the Yucatan. Something big definitely did hit, the question is what happened when it did.

Also, while not everything else is being discarded, I must admit to having a strong affinity for the impact hypothesis, simply as a matter of scale. Disease, famine, climate change, all of these happened regularly during the reign of the dinosaurs. And they were doing well, all the way up until 65 mya (the supposed 'decline' is due to paucity of fossil deposits from that time; a series in Alberta that shows from 10 my prior all the way to the extinction shows no decline). Then, all of sudden, one of the most successful vertebrate lineages ever almost completely dies out, leaving only birds behind. All of them, the world over, large and small, along with other successful groups of the time, such as marine reptiles and pterosaurs. I have a hard time believing anything less that a collosal catastrophe could have such a sudden effect.

Maybe there were other factors, maybe it worked differently from how we think, but the fact remains that they were doing fine until they vanished in a geological instant, accompanied by a huge crater and a lot of iridium dust.

[b said:
Quote[/b] ]It still does not jive because there would have been dinos that were just as/more maleable/generalist than the small mammals and herps. We are not talking species or genus level extinction here, a global event like an impact is not going to hit selectivly.

It's not the generality, it's the *amount* of food. Specialists may have been more boned that generalists, but either way, a dinosaur that needs 5 kg of meat a day is a lot worse off than a crocodile that needs 5 kg of meat a month.

If there's less food, and everyone's fighting for it, the ones who will suffer the most will be those who need the most.

Look at the predictions that makes: you survive if you need little food because you either a) have a low metabolism or b) are small (even a small endotherm). Now look at what lived: herps (which, as we know, can survive a *long* time between meals, even large ones), small mammals (they eat more than a small lizard, but not as much as a large mammal or large dinosaur),and small dinosaurs survived (now known as birds).

The real puzzle, from what I can see, is the extinction of the large marine reptiles. Given that they seem to have been denizens of the warm shallows, it's very possible their food web simply collapsed due to insufficient light and/or warmth for phytoplankton; given that ammonites, belmenites, and reef-building rudist clams all went extinct at the time, it's certainly a reasonable proposition.

[b said:
Quote[/b] ]But not all dinos were big.

Exactly, and the little ones lived on. Flight was probably a big bonus, allowing them to scour huge areas for food.

[b said:
Quote[/b] ]And some crocodyliads (that made it through) were quite large.

The truly huge ones, Deinosuchus, died. Modern-sized crocs are surprisingly economical: they can survive for a year on only a dozen or so kg of meat, especially if they brumate/hibernate for a portion of the year. They're also so long-lived that the loss of younger animals wouldn't have hurt them as badly.

[b said:
Quote[/b] ]And then there is the scavenger aspect, with all those dead bodies scavengers must have had a ton of food so why didn't T rex (assuming you accept the theory that he was a scavenger [which I am not saying I do or do not, just throwing it out as part of the argument]) make it through?

Dead bodies rot fast, though. Firstly, you've got just about every predator around out for a free meal (because even predators won't turn away a free meal). Anything that can't be eaten in a few days is too rotten. As populations drop, so do the numbers of bodies, so more predators fight over fewer and fewer corpses.

There's also the fact that a dead body can only have as many nutrients as the live animal. If the animal starved to death, it's gonna have no fat reserves left, little remaining muscles (as the body will break those down for food when starving), and not much glycogen left in the liver. It's gonna be little but skin, bones, and organ meats. That's still something, especially to a starving theropod, but it's not exactly the bounty that you'd get from carrion from healthier animals (weird as it is to call a corpse healthy; disease and such rarely strips the body to nothing before death like starvation does).

[b said:
Quote[/b] ]True, but if not that, then why do all the small critters survive over the big ones (not that all do, but the large ones always seem to go quickly) when there is a mass extinction?

Not always; trilobites, toothed birds, and other small animals died too.

However, as noted above, big animals need more food. As noted in prior posts, big animals also have smaller populations and longer generation times, leading to slower evolutionary responses.

[b said:
Quote[/b] ]I doubt that large animals could become generalists, really. Just imagine, a T-rex trying to swallow a roach? C'mon!

Well, specialist vs generalist is always size-based; what could the animal eat vs. what does it eat. False gavials are *huge* crocodilians, known to top 16 feet, thus should be able to eat just about anything, yet they've evolved into a specialist fish-eater niche.

Mokele
 
  • #30
oh yea back to the point, I got a satasfactory on my assignment, thanks guys!
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  • #31
Hey Mokele,

Before I go on I just want to say that I really am enjoying this discussion with you. It is nice to be able to go talk with someone who does not just parrot "but it is what the experts thing so it must be true". So I thank you.

[b said:
Quote[/b] ]The fact that there are other theories out there indicates that the impact theory *is* being challenged.

I take your point but I counter that unless you are really interested in it all you never really hear the other theories. Ask the Average Joe on the street and they will say it was the meteor. Period. End of discussion. You don't really have anyone making public noise about the other theories. To drag T-rex back into it, there is not Horner to the Bakker.

[b said:
Quote[/b] ]Well, we do know: we've got a worldwide iridium layer and a giant crater off the Yucatan. Something big definitely did hit, the question is what happened when it did.

I am not saying nothing hit, I am sure something did. I am just saying that it was not THE cause. There are some inconsistancies in the iridium layer and, as I noted before, there are different ways to both interpret and explain the data: Meteors are not the sole source of iridium, the layer could be the result of concentration deposition, etc.

[b said:
Quote[/b] ]Disease, famine, climate change, all of these happened regularly during the reign of the dinosaurs. And they were doing well, all the way up until 65 mya (the supposed 'decline' is due to paucity of fossil deposits from that time; a series in Alberta that shows from 10 my prior all the way to the extinction shows no decline). Then, all of sudden, one of the most successful vertebrate lineages ever almost completely dies out, leaving only birds behind. All of them, the world over, large and small, along with other successful groups of the time, such as marine reptiles and pterosaurs. I have a hard time believing anything less that a collosal catastrophe could have such a sudden effect.

Yes, disease, famine and climate change all probably happened regulary but they also were (like today) more "isolated" incidences. But at the time of the extinction you had massive global changes. You had basically every continent connected again after long isolation. You had global weather changes. Oceans were cut off from one another so currents and convection flows were disrupted. In concert it would be seriously disruptive.

[b said:
Quote[/b] ]It's not the generality, it's the *amount* of food. Specialists may have been more boned that generalists, but either way, a dinosaur that needs 5 kg of meat a day is a lot worse off than a crocodile that needs 5 kg of meat a month.

Quite true. However a dino that eats 1kg should be at least an equal match to a small mammal that eats 1kg. So why then didn't the small dinos pull through?

[b said:
Quote[/b] ]Look at the predictions that makes: you survive if you need little food because you either a) have a low metabolism or b) are small (even a small endotherm). Now look at what lived: herps (which, as we know, can survive a *long* time between meals, even large ones), small mammals (they eat more than a small lizard, but not as much as a large mammal or large dinosaur),and small dinosaurs survived (now known as birds).

Some small dinos survived as birds. However, not all the small dinos were of the same lineage that would evolve up to be birds. So why did they die?

[b said:
Quote[/b] ]The real puzzle, from what I can see, is the extinction of the large marine reptiles. Given that they seem to have been denizens of the warm shallows, it's very possible their food web simply collapsed due to insufficient light and/or warmth for phytoplankton; given that ammonites, belmenites, and reef-building rudist clams all went extinct at the time, it's certainly a reasonable proposition.

Yes it is reasonable. However it is just as reasonable to propose that a disruption of the ocean dynamic upset the balance at the lowest level. There are always alternatives.

[b said:
Quote[/b] ]Exactly, and the little ones lived on. Flight was probably a big bonus, allowing them to scour huge areas for food.

But as I noted, not all small dinos were of the lineage that would become bird. So what happened to them? Why didn't they make it? And I do agree about flight being an advantage, not only does it allow you to cover large area in search of food but it also offers a great escape from diseased areas. Or, the flipside, it is great for colonizing new areas and bringing with you something nasty that the locals don't know about.

[b said:
Quote[/b] ]The truly huge ones, Deinosuchus, died. Modern-sized crocs are surprisingly economical: they can survive for a year on only a dozen or so kg of meat, especially if they brumate/hibernate for a portion of the year. They're also so long-lived that the loss of younger animals wouldn't have hurt them as badly.

Yes, Deinosuchus died off, but IIRC he actually came after the dinos left, early in the age of mammals (or maybe I am thinking of another of the megacrocs.) Still, the point I was making was that some, not all, large crocs did make it through. And I will grant that modern-sized crocs are surprisingly economical but you still don't see them inhabiting areas like costal New England, hibernation or not. Global cooling from a dust layer would have been pretty hard on them.

[b said:
Quote[/b] ]Dead bodies rot fast, though. Firstly, you've got just about every predator around out for a free meal (because even predators won't turn away a free meal). Anything that can't be eaten in a few days is too rotten. As populations drop, so do the numbers of bodies, so more predators fight over fewer and fewer corpses.

It was a semi-rhetorical question anyways but... Yes, bodies rot fast but not everything would drop at the same time so there would be a constant (albeit deminishing) supply. And when you are talking about global death then even that diminishing supply is still pretty good sized. A small scavenger species could be quite happy and stable under those conditions.
 
  • #32
[b said:
Quote[/b] ]I take your point but I counter that unless you are really interested in it all you never really hear the other theories. Ask the Average Joe on the street and they will say it was the meteor. Period. End of discussion. You don't really have anyone making public noise about the other theories. To drag T-rex back into it, there is not Horner to the Bakker.

True, but the average joe also seems to be willing to believe that grass juice cures cancer, that seasons are caused by the earth getting closer and farther from the sun, and that said planet is 10,000 years old. With such an abysmal state of science education, I think the public's perception of the KT extinction is the *least* of our worries, and definitely not something to reproach the scientific community on.

[b said:
Quote[/b] ]I am just saying that it was not THE cause. There are some inconsistancies in the iridium layer and, as I noted before, there are different ways to both interpret and explain the data: Meteors are not the sole source of iridium, the layer could be the result of concentration deposition, etc.

I'm pretty sure it's not the *only* cause, but it's certainly a major player. As for other sources of Iridium, what can explain a worldwide deposition or a usually rare element in both terrestrial and aquatic habitats. Major volcanic eruption, maybe, but that puts us back into the "big explosion" category with the ensuring climatic effects, even if the cause is terrestrial.

[b said:
Quote[/b] ]Yes, disease, famine and climate change all probably happened regulary but they also were (like today) more "isolated" incidences. But at the time of the extinction you had massive global changes. You had basically every continent connected again after long isolation. You had global weather changes. Oceans were cut off from one another so currents and convection flows were disrupted. In concert it would be seriously disruptive.

Actually, the landmasses weren't all connected at the time:
Page showing map of earth 66 MYA

In fact, if you look at the map on the same site of 94 MYA, you don't see much difference, except that South America and Africa were a bit farther apart. Certainly nothing suggestive of massive, worldwide climatic disruptions.

[b said:
Quote[/b] ]Quite true. However a dino that eats 1kg should be at least an equal match to a small mammal that eats 1kg. So why then didn't the small dinos pull through?

Were there any non-avain dinosaur species at the time that were small enough for this to be relevant? Maybe some of the small ornithischians, but even those were pretty sizable, and a lot bigger than the mouse-sized mammals and crow-sized birds they were competing with. Most of the truly small dinosaurs I can think of are from eras before this, or are proto-birds.

[b said:
Quote[/b] ]There are always alternatives.

Hence my cynical comment about how contentious paleontology can be; we can think of alternatives, but without a time machine, all we can do is amass post-hoc evidence. With enough explaining, any amount of post-hoc evidence can be dismissed or turned to another theory. As a historical science, paleontology is essentially denied the most powerful tool of science, direct experimentation. Hence the ceaseless arguements.

[b said:
Quote[/b] ]Yes, Deinosuchus died off, but IIRC he actually came after the dinos left, early in the age of mammals (or maybe I am thinking of another of the megacrocs.)

Well, several lineages have produced huge crocs (and some sizable phytosaurs, too), both before and after. Deinosuchus was from before, probably died during the KT extinction (we think; the fossil record for the big D is very poor). The next big croc wasn't until the Miocene, some 40 MY later, namely Purussaurus.

[b said:
Quote[/b] ]Still, the point I was making was that some, not all, large crocs did make it through. And I will grant that modern-sized crocs are surprisingly economical but you still don't see them inhabiting areas like costal New England, hibernation or not. Global cooling from a dust layer would have been pretty hard on them.

Actually, gators have ranged into NC and VA in modern times, and can hibernate quite well; it's possible the ancestor of modern crocs could do likewise.

[b said:
Quote[/b] ]Yes, bodies rot fast but not everything would drop at the same time so there would be a constant (albeit deminishing) supply. And when you are talking about global death then even that diminishing supply is still pretty good sized. A small scavenger species could be quite happy and stable under those conditions.

Yep, note the *small* part. That actually does wonders for explaining mammals and birds. The former are very small, thus have low requirements. The latter, though they have higher metabolisms than, well, anything, can fly, thus covering huge areas, allowing them to last longer in the diminishing supply as both the number of bodies decreased and the space between them increased.



Ok, I've been doing some digging, and I've found several mentions of the value in the literature that nothing over 25 kg survived on land. However, inconveniently, none of these mentions, reliable as they seem to be, actually give citations of articles in the scientific literature. It's late for me, so I'll look into it more later, but it seems that there is an upper size limit for all taxa, even crocs. If there were no non-avian dinosaurs bellow that size, it would explain with only the avain lineage survived. Like I said, I'll do more digging (pun intended).
smile_n_32.gif


Mokele
 
  • #33
[b said:
Quote[/b] (Mokele @ July 27 2006,11:18)]True, but the average joe also seems to be willing to believe that grass juice cures cancer, that seasons are caused by the earth getting closer and farther from the sun, and that said planet is 10,000 years old.  With such an abysmal state of science education, I think the public's perception of the KT extinction is the *least* of our worries, and definitely not something to reproach the scientific community on.
I am with you 100% on this score. And let's not even get started on evolution in schools!!

[b said:
Quote[/b] ]I'm pretty sure it's not the *only* cause, but it's certainly a major player. As for other sources of Iridium, what can explain a worldwide deposition or a usually rare element in both terrestrial and aquatic habitats. Major volcanic eruption, maybe, but that puts us back into the "big explosion" category with the ensuring climatic effects, even if the cause is terrestrial.

I don't even know that it is necessarily a major player. Seafloor sediments and formations in Texas and Denmark suggest that the deposition of iridium took place over a span of 100K years which is way to long to attribute to a single meteor strike no matter what magnitude. The volcano source works when you consider that plate techtonics were disrupting things in such a way that there were fewer shallow seas which were the places most likely to for good sedimentation layer. With less sediment being deposited there are less thick sequences of rock and geologic time spans appear shorter than they actually were. You also need to consider that a good number of the iridium deposits occur near areas where uplift was occuring, like along the Rockies. Iridium that was being erupted from such areas would be concentrated in the few sediments deposited and as such would appear to be unnaturally concentrated.

[b said:
Quote[/b] ]Actually, the landmasses weren't all connected at the time:
Page showing map of earth 66 MYA

In fact, if you look at the map on the same site of 94 MYA, you don't see much difference, except that South America and Africa were a bit farther apart. Certainly nothing suggestive of massive, worldwide climatic disruptions.

I mis-spoke in my rush of thought, brain working faster then fingers can type. I meant that continents that had been seperated were reconnected. Your map is interesting because it is different than any I have seen which show Asia liked to N.Am., N.Am. linked to S. Am., Asia linked to Europe and Europe linked to Africa. So basically all were inreconnected.

ANd I would disagree that there was nothing massively disruptive to global climate. Opening up the deep oceans and eliminating the slew of shallow seas would have had a major effect on the climate.

[b said:
Quote[/b] ]Were there any non-avain dinosaur species at the time that were small enough for this to be relevant? Maybe some of the small ornithischians, but even those were pretty sizable, and a lot bigger than the mouse-sized mammals and crow-sized birds they were competing with. Most of the truly small dinosaurs I can think of are from eras before this, or are proto-birds.

It has been a while since I actually boned up on what all was living then but I am prety sure there were other non-avimid dinos close to the end. I could be recalling incorrectly.

[b said:
Quote[/b] ]Hence my cynical comment about how contentious paleontology can be; we can think of alternatives, but without a time machine, all we can do is amass post-hoc evidence. With enough explaining, any amount of post-hoc evidence can be dismissed or turned to another theory. As a historical science, paleontology is essentially denied the most powerful tool of science, direct experimentation. Hence the ceaseless arguements.

So very true. And something we all forget, myself included.

[b said:
Quote[/b] ]Well, several lineages have produced huge crocs (and some sizable phytosaurs, too), both before and after. Deinosuchus was from before, probably died during the KT extinction (we think; the fossil record for the big D is very poor). The next big croc wasn't until the Miocene, some 40 MY later, namely Purussaurus.

I stand corrected

[b said:
Quote[/b] ]Actually, gators have ranged into NC and VA in modern times, and can hibernate quite well; it's possible the ancestor of modern crocs could do likewise.

True but NC and VA are not really NE states and are a far cry from their temps in winter. It'd be a pretty hard hibernation with a lot of freezes.

[b said:
Quote[/b] ]Yep, note the *small* part. That actually does wonders for explaining mammals and birds. The former are very small, thus have low requirements. The latter, though they have higher metabolisms than, well, anything, can fly, thus covering huge areas, allowing them to last longer in the diminishing supply as both the number of bodies decreased and the space between them increased.

Yes, I note the small part but as I said before IIRC (always open to argument there) there were small dinos that could/should have been just as likely to fill those same roles.

[b said:
Quote[/b] ]Ok, I've been doing some digging, and I've found several mentions of the value in the literature that nothing over 25 kg survived on land. However, inconveniently, none of these mentions, reliable as they seem to be, actually give citations of articles in the scientific literature. It's late for me, so I'll look into it more later, but it seems that there is an upper size limit for all taxa, even crocs. If there were no non-avian dinosaurs bellow that size, it would explain with only the avain lineage survived. Like I said, I'll do more digging (pun intended).
smile_n_32.gif

This is interesting. I can not say I have come across that figure but then again I have not been reading as much on it as I used to. A figure like that would go a long way but it would still leave an opening for "small" dinos as 25kg is pretty sizable
 
  • #34
[b said:
Quote[/b] ]Seafloor sediments and formations in Texas and Denmark suggest that the deposition of iridium took place over a span of 100K years which is way to long to attribute to a single meteor strike no matter what magnitude.

But wouldn't seafloor sediments be expected to show a long duration, as iridium deposited on land washes out to sea?

[b said:
Quote[/b] ]You also need to consider that a good number of the iridium deposits occur near areas where uplift was occuring, like along the Rockies. Iridium that was being erupted from such areas would be concentrated in the few sediments deposited and as such would appear to be unnaturally concentrated.

Aren't there unnatural concentrations in non-uplift areas too, though? Plus, if it was the result of uplift, the iridium layer would be local, not global.

Actually, on that note, I don't seem to recall iridium generally being associated with uplifts, or anything else, really, since it's not a common element in the crust. But geology definitely isn't my strong suit.

[b said:
Quote[/b] ]Your map is interesting because it is different than any I have seen which show Asia liked to N.Am., N.Am. linked to S. Am., Asia linked to Europe and Europe linked to Africa. So basically all were inreconnected.

I seem to see the reverse; all the maps I'm familiar with of that time period show the continents separate, and the only real difference from early Cretaceous being that they're farther apart.

[b said:
Quote[/b] ]ANd I would disagree that there was nothing massively disruptive to global climate. Opening up the deep oceans and eliminating the slew of shallow seas would have had a major effect on the climate.

Yes, but over a long time period, and given that fossils show dinosaurs inhabiting a wide range of climates and migrating long distances, I'm very skeptical that non-catastrophic climate change could result in the total extinction on non-avian species, as well as so many other species, terrestrial and marine.

[b said:
Quote[/b] ]It has been a while since I actually boned up on what all was living then but I am prety sure there were other non-avimid dinos close to the end.

Sadly, my efforts to find anything in this area have been as yet unsucessful.

[b said:
Quote[/b] ]True but NC and VA are not really NE states and are a far cry from their temps in winter. It'd be a pretty hard hibernation with a lot of freezes.

However, even in the case of an asteroid impact dust cloud, I doubt there would be freezes worse than that in the tropics.

[b said:
Quote[/b] ]This is interesting. I can not say I have come across that figure but then again I have not been reading as much on it as I used to.

Well, I'm still trying to source the figure, but I'm not terribly familiar with the primary literature; paleo is more a side-interest of mine (my actual field is biomechanics).

[b said:
Quote[/b] ]A figure like that would go a long way but it would still leave an opening for "small" dinos as 25kg is pretty sizable

Well, nothing over 25 kg would include ectotherms, too. If we assume it's based on how much they eat, that's a 3 kg endotherm at the very most (generous guestimate, not actual calculation), and if small dinosaurs had avain-level endothermy, maybe even less. While some of the dromaeosaurs were likely under 25 kg, I can't think of any late cretaceous non-avian dinos under 3kg. darn, I'd kill for a simple list of known late cretaceous taxa.

Mokele
 
  • #35
There's plenty of iridium in the mantle. Tha's why Deccan Basalt volcanism at the K-T boundary is a plausible iridium source.
 
  • #36
Forgot about this thread till I saw this:

MSN article

Just food for though
 
  • #37
There's a bit of discussion of it here, including some comments by what I presume is one of the authors.

I'm skeptical (after all, that's what science is about) about some aspects, but I'll withhold total judgement until I see the actual published article so I can read their methods.

Mokele
 
  • #38
[b said:
Quote[/b] (Mokele @ Oct. 30 2006,10:31)]I'm skeptical (after all, that's what science is about) about some aspects, but I'll withhold total judgement until I see the actual published article so I can read their methods.
Funny, those were my exact thoughts. THere do seem to be some rather "vague" asertations that need backing. But like I said, it was just food for though. I was just glad to see an alternative theory comeout of the dark corners and into the light. Even if it is wrong it gets people thinking
 
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