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Egg-laying, Not Environment, May Explain the Size and Downfall of Dinosaurs
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."
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?
Sheesh, evil *and* a jerk. -- Jade
> 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?
Sounds like the ultimate free market.
Those who do not learn from commit history are doomed to regress it.
If he really exists, then he's an idiot.
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'.
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?
Reptilian eggs are not quite the same as avian eggs.
Moron.
I've read much of this before and it still seems pointless. People keep trying to explain how dinosaurs were such poor survivors yet they are by far the most successful large terrestrial species the planet has seen. The egg thickness theories have nothing to do with dinosaurs suddenly disappearing. The only thing it really explains is why dinosaurs had to have such a rapid growth rate. They ranged in size from around the size of a chicken to nearly the size of a Blue Whale with the largest eggs being not much larger than an Ostrich egg and the smallest on pare with a chicken egg. Those conditions existed for tens of millions of years before their extinction so egg size and shell thickness couldn't have been a factor in their extinction. Mammals also didn't suddenly change towards the end of their reign so it's unlikely that they suddenly found dinosaurs and their eggs tasty. The mammals driving dinosaurs into trees is silly since birds had been around for tens of millions of years before their extinction and T-Rexs didn't suddenly decide they had to climb trees. Birds were better at exploiting the nitch than the flying reptiles. Like most extinction events it's complicated and other than the meteor impact there aren't any smoking guns. Odds are it was climate change than was the death blow to the ones that survived the impact. The more interesting fact is the only species that survived were either small so they needed less food or they were able to go for long periods without eating like Alligators. Odds are most starved to death since some were even cold adapted and survived in higher latitudes than even alligators so the freezing theory wouldn't explain all the deaths. Ultimately the best explanation is starvation brought on by climate change caused by a meteor strike. Odds are it was that simple.
The gowns (usually from Ivy League Geo departments) who bitterly fought the Alvarez asteroid theory failed but next proposed that the dinos were already stressed out and headed for extinction when the asteroid hit. Now this...ugh, will they never give up?
Let's not forget that as a class the dinosaurs did not completely die out. It is now accepted that birds are a continuation of the dinosaur line.
How does this theory account for the megafauna? The giant sloth, the american lion, etc.
What was first, the chicken, the egg or the dinosaur?
I was promised a flying car. Where is my flying car?
So... they're saying dinosaurs grew so large for the same reason men buy Hummers?
When someone says, "Any fool can see
I like this phrase. As long as people understand a difference between "explanation", "fact" and "possible explanation", the science is in a good shape
I do not believe in karma. "Funny"=-6. Do good and forbid evil. Yours, Oft-Offtopic Flamebaiting Troll.
Dinosaurs probably had a dual air sac respiratory system like birds do today. This respiratory system allows continuous oxygenation of the lungs, unlike mammals who breath in and out. This is a very robust system and may be the reason that early dinosaurs out-competed early mammals et al and established a dominance in the Triassic that continued until Chicxulub.
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.
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.
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.
I only look human.
My mother is a halfling and my dad is an ogre, so that makes me an Ogreling
...they grew to that size due to having longer lives, and a massive event occurred with the only salvation from the event being something that allowed smaller animals to be aboard, without the long life afterwards.
But was all know that since science can't prove that that it absolutely couldn't happened that way, now don't we?
Please provide proof of a location of dinosaur fossils that is above the K-Boundary.
There are none.
They were long gone and buried deep before the Space Rock From Hell [tm]
For any given complex problem there is always a quick and simple answer that is absolutely wrong - A Einstein