Egg-laying, Not Environment, May Explain the Size and Downfall of Dinosaurs 123
ananyo writes "Paleontologists have argued that dinosaurs were able to grow quickly and fuel large bodies when temperatures were warm, oxygen levels were high, and land masses such as the supercontinent Gondwana provided abundant living space. But two new studies contradict that idea and suggest the key to some dinosaurs' vast size lies in the limitations of egg laying. In the first study, researchers examined whether changes in body size followed changes in environmental factors and found no correlation. A second study argues that the reason dinosaurs grew so large was because they were forced to produce relatively tiny young (abstract only), as developing embryos would not be able to breathe through the thick shells of large eggs. When the young of large animals start out small, they must grow through a large size range before reaching adulthood. As a result there was intense competition between small and medium-sized dinosaurs, forcing adults to keep growing until they reached very large sizes to gain a competitive edge. But being big also had drawbacks. When an asteroid impact 65 million years ago wiped out most large-bodied animals, there were so few small dinosaur species that the group was almost obliterated, with only the birds surviving."
Circular reasoning? (Score:5, Interesting)
When the young of large animals start out small, they must grow through a large size range before reaching adulthood. As a result there was intense competition between small and medium-sized dinosaurs, forcing adults to keep growing until they reached very large sizes to gain a competitive edge.
IOW, dinosaur species had to be big, because young dinosaurs of big species had to become big?
Re:Circular reasoning? (Score:5, Insightful)
Re:Circular reasoning? (Score:5, Interesting)
I think the actual implication would be that big dinosaurs had to produce vast numbers of young, so that enough of them would survive to become full-sized adults.
Also, "the little ones get eaten" would apply to small species of dinosaurs - and mammals. (Unless most predators preferred the taste of chicken to the taste of beef.)
Re:Circular reasoning? (Score:5, Informative)
I RTFA and it looks like hogwash to me. It said that the adults had to be big to keep from being eaten by their own young. It seems to me that cannibalism would be an evolutionary disadvantage, plus the biggest dinos were herbivores. And I notice that most large animals today are herbivores -- elephants, cows, rhinos.
Perhaps the article was poorly written, but it doesn't seem logical. The only logical part was that the larger animals became extinct when the asteroid hit.
Re:Circular reasoning? (Score:4, Interesting)
Cannibalism is a distinct evolutionary advantage when there is too few resources to support population that has to birth a lot of young to ensure at least some of them survive to adulthood.
It's commonly practised among many species that fall within this umbrella to this day.
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In Niven and Pournelle's The Legacy of Heorot they claim there is a species of frog that survives by eating only its own tadpoles. The continually lay frogspawn, which grows in tadpoles that eat algae and the like, and the parent frogs eat (most of) the tadpoles. I have no idea if this is true or not (it's only a novel), but I always suspected it was. Anyone know the species?
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In Canada, we refer to them as the Bloc Quebecois.
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Spadefoot
http://www.centre.edu/web/news/2009/brian_storz.html [centre.edu]
Re:Circular reasoning? (Score:4, Insightful)
It seems to me that cannibalism would be an evolutionary disadvantage...
In order for a species to survive, an animal only needs to survive long enough to produce children who can survive long enough to produce their own. Once you're old enough to survive to the point of reproduction, how does snacking on a parent hurt anything? In fact, if the parent isn't providing anything that helps you survive, you're just having a meal and cutting down on competition.
"It's people! You're eating PEOPLE!"
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There are multiple problems with this rationalization:
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"I RTFA and it looks like hogwash to me."
Well, what do you expect from a science where no direct observations can be made, no experiments can be performed, and all of your theories are based on fossils millions of years old? While I wouldn't say the study of subjects like this are a waste (things can still be learned from them), these theories have to be taken with more than the usual number of grains of salt.
IMO every set of theories on a subject like this is built up from the bottom like a house of cards.
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Yeah, right - because "In the beginning God .... " is such a logical framework.
Or, are you more of a 'turtles all the way down' sort of guy?
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I RTFA and it looks like hogwash to me. It said that the adults had to be big to keep from being eaten by their own young.
You don't have kids?
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Re:Circular reasoning? (Score:4, Insightful)
Right! Essentially, as the source story says, dinosaurs ended up competing with their own young in a way that mammals didn't. Mammals were able to occupy all niches - ie niches appropriate for small and medium sized animals, while adult dinos had to keep getting larger and larger to keep their competitive edge. The two papers are pretty neat and work well together - one shows the traditional hypothesis isn't right (environment doesn't correlate to dino size), the other suggests a credible reason why.
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Evolution has the advantage of being dependent on time and space, making mathematical logic completely irrelevant to how nature actually works
That's silly. The GP was just oversimplifying the situation. That mistake hardly makes mathematical logic irrelevant to evolution or nature.
If you had a valid point, what was it?
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I should have been clearer and said, "If you had a valid point pertaining to the bit of your post I quoted, what was it?". I agree with you on the part I did not quote.
About the part I quoted, you made a blanket statement about mathematical logic and nature that's clearly false: mathematical logic is highly relevant to how nature actually works, for instance with "time series generalized least-squares regression models" mentioned in the first journal article's abstract. I was just wondering if you had a goo
Re:Circular reasoning? (Score:5, Insightful)
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Still sounds like unnecessarily convoluted logic. There's no reason the young of big dinosaurs wouldn't be able to compete with smaller species as well as they had before.
A simpler explanation would be that post-KT there wasn't an ecosystem to support the huge adults, and when the environment won't support adults the whole species dies.
I think the summary is just making too much of the relevance of the articles to extinction.
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There's no reason the young of big dinosaurs wouldn't be able to compete with smaller species as well as they had before.
Unless of course the adults were interfering with the others to make their own young more able to compete.
Though that doesn't jibe with the "because they had to compete with their own young" line.
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A simpler explanation would be that post-KT there wasn't an ecosystem to support the huge adults, and when the environment won't support adults the whole species dies.
I think the idea is, when you are born small (category A ecosystem), than grow mid-size (category B ecosystem) than very-large (category C), you need all these different ecosystems intact in order to achieve a full circle. And you need those 3 categories to coexist in relative close proximity, if not at the same location.
When you are born category A and remain category A, you only need a category A ecosystem to survive and category B/C ecosystems don't matter at all.
So let's say a big event, destroyed part
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"Why don't animals today get bigger and bigger today?"
Haven't you been to the mall recently? As a population, humans are getting a *LOT* wider...
FTFY.
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In the case of homo sapiens, the species seems to already have a gene that makes it want to gang up and kill any member who looks different so such a mutation would hardly be viable.
They're quite viable. We put them on sports teams and give them an increased chance to succeed.
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Sort of. All those tiny brachosaur babies were tough competition to all other small dinosaurs. And since all dinosaurs had to start small, the niche of 'being small' was hopelessly overpopulated, so they grew big to occupy another niche.
Re:Circular reasoning? (Score:5, Interesting)
Virg
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No, the point is that bigger specimens of smaller dinosaurs had an advantage over the average, so there was environmental pressure driving larger animals to survive. Therefore, as the bigger dinosaurs bred more than their smaller siblings, the average size of their young went up, reinforcing their advantage until truly huge specimens became the norm.
Now that actually makes sense, though as others have pointed out, why didn't the same apply to mammals?
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Aha, but how many dinosaurs were actually cold-blooded? The current ones certainly aren't, they run hotter than mammals (though they are certainly also tiny compared to some of the huge ones of the past).
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No, the point is that bigger specimens of smaller dinosaurs had an advantage over the average, so there was environmental pressure driving larger animals to survive. Therefore, as the bigger dinosaurs bred more than their smaller siblings, the average size of their young went up, reinforcing their advantage until truly huge specimens became the norm.
Virg
Actually, there is no proof that bigger specimens of smaller dinosaurs had an advantage over the average. Being bigger may also mean being slower. Being slower would mean less likely to capture food (if a hunter) or more likely to be captured (if hunted). In addition, what may work to the advantage of one species may not be to another. It simply is not possible to make a blanket statement that bigger specimens of smaller dinosaurs had an advantage over the average ones.
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The explanation was extremely poor. Hopefully this is less poor.
Start with this factor: eggs have to be small. If they are too large, the short of it is, the oxygen/volume ratio in the egg will get too low.
Now, consider that all of the large species started as eggs. Therefore their young start small.
Now, they have to compete with the smaller and medium sized creatures to become large. To reduce the time-frame of this competition, they have to grow fast, to grow fast they have to use a lot of resources. Resu
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Less poor, but actually sounds like an environmental pressure to favor small species rather than large ones - the opposite of what the articles seem to be saying.
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Has anyone noticed that humans are getting larger? When I was 20, average height for men was 5 foot nine, now it's six feet.
When food is plentiful, animals get larger, since size keeps one from being easily eaten. When food is scarce, large animals starve while small animals survive, since a small animal dosn't need much food.
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While you would be big in Japan... (Score:2)
While you would be big in Japan at 180, I would be "Huge" in Japan at 275! Like Godzilla.
And just like these dinosaurs, that simple fact alone makes me better than you. I blame your "low" weight on your name, dietdew7.
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It's a side effect of all the antibiotics in the meat. Continued low-level doses of antibiotics cause mass increase. That's still in the meat you eat, so you've got the same low-level antibiotic exposure.
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I suspect it has something to do with some of the hormones they feed beef, like bovine growth hormone. But when I was in Thailand in 1974, I was a gaint compare to the Thais, who ate hardly any meat; their dists consisted mostly of rice. A couple of years ago we had a Thai intern who was as tall as me, and she said that's normal for them now. Not evolution, of course, but diet.
However, if there's a severe scarcity of plants for an extended period (like after the ateroid strike), larger herbivores are going
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No, it's not. Average height for a human male is about 5'10" in the USA. Worldwide, it's shorter than that...
Human height has increased somewhat since the 19th century, mostly due to better childhood nutrition.
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No, the argument is actually against small species, because that's where all the competition was. Butt hey had to start small - so they tried to jump through that phase quickly. Once you are larger, the competition with the smaller species is reduced. It's only once being larger became unfavorable, that they had issues.
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I bet this would have been a hot topic of discussion around the Triceratops carcass. Which came first, the Dinosaur or the Egg? Who knew the T-Rex was such a philosopher.
Probably came about from pondering why the fuck they were born with such short arms.
Re:Circular reasoning? (Score:5, Funny)
Probably came about from pondering why the fuck they were born with such short arms.
Couldn't reach a conclusion?
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T-Rex had tiny arms to compensate for the increased weight of its gigantic murder-maw.
It had arms at all because they helped it stand up (and maybe other uses). Skeletons show both many more muscle attachment points than would be needed for vestigial arms, and stress marks from bearing the weight of its body. Its arms were tiny, but very strong.
Re:Circular reasoning? (Score:5, Insightful)
As near as I can tell, the argument is...
Premises:
(1) Dinosaurs had some initial size diversity due to environmental factors
(2) Egg sizes were limited because thick shells would be air tight
(3) Egg-laying dinosaurs went through large size variances as they grew to adulthood (compared to mammal-scale)
Reasoning:
* Because of (1), (2), and (3), a particular species would occupy a broader environmental niche, eg. with small juveniles going places adults couldn't reach
* Increased niche breadth would cause species to interact and compete more with other species
* Increased competition results in a size arms race since larger animals get food more, which incidentally increases niche breadth all the more
* The process doesn't continue indefinitely since large sizes eventually hit environmental constraints, though "steady-state" sizes would be larger in egg-laying dinosaurs than eg. mammals. Birds have strong environmental reasons to stay small that tend to overcome increased competition.
[If you're a biologist, preferably one who has read the paper, please correct me if I'm wrong. The Nature article is pretty vague and I can only read the abstract of the journal article.]
Re:Circular reasoning? (Score:4, Insightful)
If the size of the eggs themselves has a limit, then all dinos start out small, regardless of how big they end up
There are risks in being a growing animal: Until the creature settles down to its adult size, it has to adapt to different food sources, learn over and over again how to move efficiently at each new size, and expose itself to predators foraging for food. Growing animals are awkward at some stages, and need more food, more often than when they finish growing.
Triple your size in a year and get it over with, those risks are proportionately small. Double over and over again every six weeks, and those risks are much larger.
So, there needs to be some advantages once you get big, to offset the disadvantages of the growing years. If a species has more disadvantages than competitors, and doesn't have advantages, it dies out from the competition. But the advantages of growing bigger than a competitor species accumulate with very large sizes:
For example, there's not much advantage to being just a little larger than a pack hunter such as Deinonychus, but if, like Apatosaurus, you're so large your hide is thicker than the packs 6" killing claws and so tall the pack can't even reach your vital spots, the advantage is your adult species members are practically totally immune to Deinonychus attacks. To eat you, Deinonychus doesn't just have to evolve to be a little taller, it has to evolve in the direction of T-Rex.
There are other trends in dino evolution: By the time smaller, early fast predators actually get to T-Rex size descendants, all the Apatosaurus like dinos are gone, and horned and armored herbivores take their places. Bulk can only do so much, and it's hard to see how anything could simply get big enough to ignore a pair of T-Rexes attacking it. But these biologists aren't saying that the trend towards bigness overwhelmed all other factors, just that it was a more major cause of more effects than is immediately obvious.
You can call all this circular reasoning. The biologists are in effect arguing that the advantages and disadvantages must have pretty well balanced in each stage of evolutionary history, because natural selection must work as the theory. But there are other, non-circular, lines of thought which support this. Reducing Darwin to "Survival of the Fittest" is tautological, but when you use actual math on the actual fossils, and look at how many different species in different size groups there were, over the millions of years leading up to the extinction event, you get non-circular predictions as well, like that number of different species would taper off for the last few million years before the extinction, and that it would be lower by far than for most typical dinosaur eras.
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Few is not the same as none (Score:4, Insightful)
> there were so few small dinosaur species that the group was almost obliterated, with only the birds surviving
Yes, but why didn't those few non-bird species survive? Or did they mean that birds were the only small dinosaur species?
Re:Few is not the same as none (Score:4, Interesting)
Also, why didn't those small juvenile dinosaurs just grow up and repopulate the world?
It's not like there would have been a shortage of them post-asteroid. If anything, the juveniles would have had an unusual edge, since they were growing up into a vacuum where the big predators used to be.
Re:Few is not the same as none (Score:5, Interesting)
That seems to make quite a bit of sense to me; an big asteroid impact would throw a lot of dust into the atmosphere, so a prolonged period of cooling would likely result. That could reasonably be expected to lead to a significant reduction in the available foliage for consumption by herbivores, leading to the larger herbivores being the first to starve to death. Fewer herbivores, means less meat for the carnivores, so the big predators are the next to find that the larder has suddenly gone dry, and down the chain it goes.
The most likely survivors in that scenario are those that can survive on meagre food supplies and digest more of what is available; if you can eat branches and the trees are bare, those of your competitors that require more succulent fare are going to have a harder time of things. Similarly, those species that relied more on stealth/cunning than just sheer numbers to survive would have have more of their preferred diet to go around and/or be more likely to avoid predation.
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So at first there would still be a lot of small babies of big (dead) dinosaurs to compete with the smaller dinosaurs (that evolved into birds?) from the short grasses that would emerge post fireball.
Birds evolved well before the KT event. The dinosaurs that were still dinosaurs at the time simply died out.
Good points btw.
Re:Few is not the same as none (Score:4, Insightful)
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The juveniles of existing large dinosaur species would have starved when they grew too large due to the lack of foliage for the herbivores. As they were juveniles, they would not have reproduced until they grew to adulthood, and thus they would have starved before reproducing. Ironically, if they were better "designed", then they could have survived in smaller forms until the time was right again. Instead, only the dinosaur species with the smallest adult forms survived.
As for smaller dinosaurs/birds, who i
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Using the same reasoning: The birds were able to fly, and only the flying dinosaurs lived.
Dom
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Using the same reasoning: The birds were able to fly, and only the flying dinosaurs lived.
Then why didn't non-flying mammals die?
"small && ( mammal || flies)" doesn't really make a lot of sense.
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Economics (Score:1, Interesting)
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Sounds like the ultimate free market.
Yes, every meal was "all you can eat".
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They forgot to hire lobbyists to convince the government they were "Too big to fail."
God is an idiot. (Score:1, Offtopic)
If he really exists, then he's an idiot.
Re:God is an idiot. (Score:4, Funny)
If he really exists, then he's an idiot.
Clearly, the dinosaur god couldn't compete. It's down to the human god vs. the beetle god now.
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When asked for their views on the origin and development of human beings, between 40% and 50% of adults in the United States say they share the beliefs of young Earth creationism, depending on the poll. The percentage of believers decreases as the level of education increases—only 22% of respondents with postgraduate degrees believed compared with 47% of those with a high school education or less.
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only 22% of respondents with postgraduate degrees believed
"Only"!?
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Well if you are going to bring theology into it. You could argue that God Created Dinosaurs, to keep the Mammals down and small, until after the asteroid hit, so we would then evolve into what we are now. If we to be designed to be made in his image, then there are particular circumstances that needs to happen to do that. Yes I am using Intelligent Design Theory to explain this, so don't consider this argument science. However your argument is that if God Exists then he's an idiot, is not based on scien
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I'd say to the GP "You're calling an entitty who is intelligent enough to design and build math, physics, time, and the entire universe an idiot? Only an idiot woud say something so stupid. To think that a mere human could understand the motives of a being that powerful is the very height of idiocy".
Summary == Gibberish (Score:1)
Does nobody read the summaries before posting them? According to the reasoning shown in summary, we should be seeing adult sparrows in the 40+ ton range, because they're 'forced to produce such tiny young'.
Re:Summary == Gibberish (Score:5, Funny)
Does nobody read the summaries before posting them?
Yes, nobody reads everything.
Except a 40ton sparrow couldn't fly (Score:2)
Any non flying bird is at a serious competetive disadvantage to birds that do fly unless its some niche ecosystem such as new zealand with few competitors or they've learned to "fly" underwater , eg penguins. Sure, ostriches are fairly big , but they haven't exactly taken over the world have they?
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It would probably have trouble breathing too.
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Note that for ten or so million years after the asteroid, the dominant land animals were...great big non-flying birds.
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Google "Terror Bird". :)
Doesn't explain anything (Score:5, Insightful)
This myth dies hard (Score:2)
Megafauna? (Score:2)
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Quite likely with a little help. Hunting may not have been enough to wipe them out alone, but it was at least a contributing factor.
chicken? (Score:2)
From little acorns (Score:2)
"May explain" (Score:3)
I like this phrase. As long as people understand a difference between "explanation", "fact" and "possible explanation", the science is in a good shape
Maybe it is because they could (Score:3)
We already know that terrestrial arthropods, like insects, are limited in size by a combination of the O2 concentration in the air and the tracheal respiratory system (a network of tubes...). So it would not be surprising that a highly effective dual air sac respiratory system could be efficient enough to make the trade-offs for increased size more advantageous for dinosaurs than mammals.
Therefore, for dinosaurs, increasing size to compete may have been more evolutionary advantageous than for mammals. And that is why dinosaurs grew so big.
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then why are birds small?
Mobility (Score:2)
I am certainly not a paleontologist, but it seems to me that there is evidence of a filter :
Birds (air-mobile) - mostly survived. My understanding is that there wasn't even that big a restriction in the number of species.
Dinosaurs (not air-mobile) - entirely wiped out.
This, to me, indicates that there was some sort of premium on air mobility. Maybe there were enormous tsunami's, and you had to be aloft to survive.
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Land-locked mammals probably had trouble competing in the same niche as birds. Probably why birds are still hugely successful (some species even thrive sharing territory with highly competitive humans). Non-flying birds are restricted to rather unusual habitats (like Antarctica, New Zealand, ...), so there must be something to be said for good, old-fashioned mammals as well.
Note that birds have rather high energy requirements (high body temperature, and flying is expensive), so that may be why they lose out