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Old 08-10-2017, 12:18 AM
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Why are there no dinosaur-size land animals today?


Some scientists say that the enormous Patagotitan mayorum is the largest animal ever to walk the earth. Why are there no land animals of the size of the biggest dinosaurs today? What's changed about the planet? Presumably it's still possible for land animals to get that big and the evolutionary advantages of massive size are pretty obvious; who's going to prey on something like Patagotitan? So why no giant beasts today?
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Old 08-10-2017, 01:56 AM
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Some scientists say that the enormous Patagotitan mayorum is the largest animal ever to walk the earth. Why are there no land animals of the size of the biggest dinosaurs today? What's changed about the planet? Presumably it's still possible for land animals to get that big and the evolutionary advantages of massive size are pretty obvious; who's going to prey on something like Patagotitan? So why no giant beasts today?
There are disadvantages in growing too large. For large animals it takes time to reach sexual maturity for just a few offspring produced and many young will die before reaching adulthood. It takes a lot of investment by the parents, so such groups will be more vulnerable to adverse changes in the environment and predation compared to smaller animals who can produce more offspring and don't need to invest as much time and effort in rearing their young. You're also more conspicuous to would-be prey if you are too big and nimble prey will be able to elude you easier.

Last edited by abashed; 08-10-2017 at 01:59 AM.
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Old 08-10-2017, 02:04 AM
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Dinosaurs laid eggs which meant they produced several embryos at once, which promoted the chances of survival of their young that much more.
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Old 08-10-2017, 03:42 AM
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But all the disadvantages you cite would have been around when large dinosaurs were alive. They coped with them, grew huge and still managed to thrive. Why shouldn't later animals have adopted the same strategy? What is so different about today?

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Old 08-10-2017, 04:14 AM
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But all the disadvantages you cite would have been around when large dinosaurs were alive. They coped with them, grew huge and still managed to thrive. Why shouldn't later animals have adopted the same strategy? What is so different about today?
For one thing there was more oxygen about which promotes growth, although this is just a hypothesis and quite controversial.

As I said, dinosaurs laid eggs, therefore, reproduction would not have been such a problem, whereas mammals only make one or two young and if they fall prey to disease or lack of food it takes the population a lot longer to recover. Dinosaurs could simply lay more eggs. I daresay, also, that mammalian young require more rearing than dinosaur young did which puts a premium on the parent's time and energy. Look at elephants and the way their young have a long childhood requiring much parental care. If a calf dies for some reason it will take a long time to replace that individual.

It's also possible that sauropods were able to swallow large amounts of food without chewing, increasing body size and permitting the development of bird-like breathing allowing oxygen to be supplied to their bodies more efficiently.

There is no one reason why today's animals are not as large as dinosaurs but a complex of reasons.

Last edited by abashed; 08-10-2017 at 04:17 AM.
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Old 08-10-2017, 05:05 AM
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There's a maximum possible size for land mammals, and it's around 1/10 that of land reptiles. At least, that's this person's theory.
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Old 08-10-2017, 05:16 AM
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There's a maximum possible size for land mammals, and it's around 1/10 that of land reptiles. At least, that's this person's theory.
Interesting and goes to show what I said about there being a number of reason why land mammals never got as large as the largest dinosaurs.
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Old 08-10-2017, 06:01 AM
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Two factors to conciser: there may have been no need to get that large, and there may have been no way to get that large.

For not need, dinosaurs may have been caught in a feedback loop of bigger predator pushing bigger prey pushing bigger predator pushing bigger prey, and there may be a practical limit on how big a mammalian predator can get, allowing mammalian prey to not need to get particularly huge (and mammals tend to get fast to avoid predators, not get big.)

For no way, mammals, being warm-blooded, may be faced with 1.) not being able to find enough food for a giant body or 2.) not being able to shed enough heat for a giant size, with possibly an evolutionary constraint that prevents them from vastly changing their metabolism. The biggest whales get around this by being filter feeders and by living in water, which sucks out the heat more quickly than air (so much so that they need extra fat.) (Some dinosaurs may have been warm-blooded, but they may have been differently warm-blooded enough that this wasn't a limit on size.)
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Old 08-10-2017, 06:54 AM
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Why are there no dinosaur-size land animals today?


They changed the tax codes.
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Old 08-10-2017, 07:59 AM
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Nowadays, an elephant is already big enough that nothing can prey on it. Why go bigger?

Of course, elephant-size wasn't big enough for that at the time of the dinosaurs, because there were bigger predators, too. So that suggests an evolutionary arms race of size.

So maybe the answer is just that the evolutionary arms race hasn't had enough time, since the K-T event, to build back up that far.
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Old 08-10-2017, 08:04 AM
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There are plenty of reasonably large mammals (less so now, mostly due to human predation).

The true giants among dinosaurs were the Titanosaurs. Perhaps it is simply a matter of random chance why these creatures developed extreme hugeness.

After all, the largest sea creatures ever to live were the Blue Whales - one could equally ask why no predecessor creatures ever grew that large.

Some land mammals grew to pretty enormous size though:

http://mentalfloss.com/article/66361...nd-mammal-ever

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At such an impressive size, Palaeoloxodon namadicus would’ve not only outweighed Paraceratherium, but possibly certain long-necked dinosaurs like Camarasaurus as well. The behemoth died out around 24,000 years ago.
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Old 08-10-2017, 08:31 AM
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So maybe the answer is just that the evolutionary arms race hasn't had enough time, since the K-T event, to build back up that far.
Well, the evolutionary arms race took a different track and becoming huge didn't particularly help.
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Old 08-10-2017, 08:33 AM
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Nowadays, an elephant is already big enough that nothing can prey on it. Why go bigger?
Humans prey on elephants. We may have been the leading cause of the extinction of its relative in the Americas, and we may yet send them into oblivion in Africa, as well. But also, there are some lion packs that seem to specialize in preying on elephants.
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Old 08-10-2017, 08:52 AM
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Humans prey on elephants. We may have been the leading cause of the extinction of its relative in the Americas, and we may yet send them into oblivion in Africa, as well. But also, there are some lion packs that seem to specialize in preying on elephants.
Indeed, it is quote possible our stone age hunter ancestors played a role in the extinction of the above-noted gigantic species of elephant. I doubt gigantic plant eating dinosaurs would have fared any better, had they existed.
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Old 08-10-2017, 09:04 AM
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Just an amazing coincidence that all the megafauna dies off as soon as humans arrive ...
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Old 08-10-2017, 09:08 AM
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OK, I should have said that elephants have no predators other than humans. But we've been on the scene only for a very short amount of time, not long enough for any significant evolutionary changes other than extinction. And more size wouldn't help against us, anyway. Elephants are big enough to stop any predator that can be stopped by size, so the point remains that there's no advantage for them to be bigger.
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Old 08-10-2017, 09:18 AM
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This site makes the good point that the fact that the biggest known elephant relative and the biggest known rhino relative are more or less tied for size (as best as we can determine) may indicate that this is the size limit for land mammals. (That article also links to this relevant one.)
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Old 08-10-2017, 09:35 AM
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I thought the prevailing theory on Mammoth extinction was climate change causing loss of habitat and thus food and not humans? As the ice age ended the Mammoths did not adapt quick enough as forests replaced tundra.
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Old 08-10-2017, 09:42 AM
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I thought the prevailing theory on Mammoth extinction was climate change causing loss of habitat and thus food and not humans? As the ice age ended the Mammoths did not adapt quick enough as forests replaced tundra.
It is possible, but a problem with this theory is that numerous other warm periods had occurred during the existence of the mammoths, similar to the end of the last ice age to today, but the mammoths did not die out during any of these.

It is also possible that the warming trend did reduce mammoth populations, but that the "killing blow" was then landed by human predation on this diminished population.
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Old 08-10-2017, 09:44 AM
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I thought the prevailing theory on Mammoth extinction was climate change causing loss of habitat and thus food and not humans? As the ice age ended the Mammoths did not adapt quick enough as forests replaced tundra.
There is no spoon consensus.
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Old 08-10-2017, 10:26 AM
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Being that big comes as a package deal including the environment and every aspect of it.
That environment ceased to exist and i dont think has existed ever since.
If the world itself can't support you being that big, you cant be, mutation or adaptation towards that end would be a failed path.

There are a lot of reasons why ultra megafauna worked for 300 million years, the more scientific persons here could give you exact details as we know them, but its a complex combo deal, and it hasnt existed for 65 million years.

Even the mammalian ultra mega fauna combo deal ended, leaving us the few hardy yet smaller survivors we have today.

One super important thing that you need is, FOOD, the world has to be able to feed your ultra mega fauna.
If you are going to be titanic of proportion, the world needs to be overflowing with mass quantities of high density nutrition.
That does not exactly describe the current crap selection of grasses and leaves our current feed stock mega fauna survive on.

No need for titanic carnivores , if you dont have a vast supply of titanic herbivores, right?
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Old 08-10-2017, 10:39 AM
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OK, I should have said that elephants have no predators other than humans. But we've been on the scene only for a very short amount of time, not long enough for any significant evolutionary changes other than extinction. And more size wouldn't help against us, anyway. Elephants are big enough to stop any predator that can be stopped by size, so the point remains that there's no advantage for them to be bigger.
Did you miss the part about lions? And African lions are not the largest predators that have existed, or even the largest mammalian predator that has existed (or exists, since some species of tigers are bigger; but then tigers hunt alone).

Last edited by John Mace; 08-10-2017 at 10:40 AM.
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Old 08-10-2017, 10:53 AM
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Actually, I think the prevailing scientific consensus is that humans played a very important role and probably decisive role in most regions. Climate change may have also been important in some limited areas and for some species. But in general, megafaunal extinction is better correlated with the arrival of modern humans than climate change.

As noted in the article, mammoths survived on islands much longer than they did elsewhere even though these islands were also subject to climate change.
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Old 08-10-2017, 11:01 AM
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I thought the prevailing theory on Mammoth extinction was climate change causing loss of habitat and thus food and not humans? As the ice age ended the Mammoths did not adapt quick enough as forests replaced tundra.
Dont think it is quite that simple, i don't think we exactly know what complex thing was going on.

But i also don't believe the simple"Man killed them all" theory either.
If you take north america as an example, we are talking about a low density, low birthrate, high mortality population of hunter gatherers, not the plains buffalo hunters.
At best, i figure they simply sped the clock up a tick on an already begun dying event.

Many things died that they are not even noted to have been eating and were not predators.
And Some large surviving things became smaller.
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Old 08-10-2017, 11:12 AM
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For one thing there was more oxygen about which promotes growth, although this is just a hypothesis and quite controversial.

As I said, dinosaurs laid eggs, therefore, reproduction would not have been such a problem, whereas mammals only make one or two young and if they fall prey to disease or lack of food it takes the population a lot longer to recover. Dinosaurs could simply lay more eggs. I daresay, also, that mammalian young require more rearing than dinosaur young did which puts a premium on the parent's time and energy. Look at elephants and the way their young have a long childhood requiring much parental care. If a calf dies for some reason it will take a long time to replace that individual.

It's also possible that sauropods were able to swallow large amounts of food without chewing, increasing body size and permitting the development of bird-like breathing allowing oxygen to be supplied to their bodies more efficiently.

There is no one reason why today's animals are not as large as dinosaurs but a complex of reasons.
What's the mechanism for higher oxygen levels promoting growth? I haven't looked into it but it sounds fairly dubious to me.
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Old 08-10-2017, 11:21 AM
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As noted in the article, mammoths survived on islands much longer than they did elsewhere even though these islands were also subject to climate change.
But said mammoths had their own unique adaptation going on which may play a part
of their longer survival.
Shame no surviving pygmy mammoth to study what adaptations it has made.
Santa Rosa didn't show signs of hunting? Yet they die eventually.
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Old 08-10-2017, 12:34 PM
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Did you miss the part about lions? And African lions are not the largest predators that have existed, or even the largest mammalian predator that has existed (or exists, since some species of tigers are bigger; but then tigers hunt alone).
And bears are much, much larger than tigers
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Old 08-10-2017, 12:42 PM
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And bears are much, much larger than tigers
Lions < Tigers < Bears.

OH MY!!
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Old 08-10-2017, 12:57 PM
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And bears are much, much larger than tigers
The muchness of bearses largerness than tigers is much smaller than the muchness of larger than lions of the largest theropods.
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Old 08-10-2017, 01:24 PM
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Maybe those huge sauropods simply never evolved any system for growth regulation other than availability of food, and so continued to grow for their entire lifespan? Some of the fossils we find might well be from bicentenarians...

Whereas, once some control mechanism had evolved, as it has in mammals, it would probably be an advantage, as it would save resources otherwise wasted on increasing body size for reproductive purposes.
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Old 08-10-2017, 01:24 PM
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[snip] ... But i also don't believe the simple"Man killed them all" theory either ... [snap]
Neither do I ... the whole notion of humans hunting down and eating every last horse across the entire continent in a rather short time in preposterous ... but this predation was a major stressor ... along with climate change ...

One more major stressor that rarely comes up in these discussions is that humans brought fire with them ... and humans knew how to use fire to modify the environment to their benefit ... and not necessarily to anything else's benefit ...

Each one of these three mechanics alone wouldn't have driven so many species into extinction ... but bring the three (and however more) to bear all at once ... we have ecological catastrophe ...

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Old 08-10-2017, 03:29 PM
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the whole notion of humans hunting down and eating every last horse across the entire continent in a rather short time in preposterous
The Passenger Pigeon would like to disagree. As would the Tasmanian Tiger and a bunch of others. And those only took a few tens of years. We're talking a timescale of centuries, and many fewer animals to begin with. I'm not saying it's true, just that it's not at all preposterous that humans can wipe out a species in a very short time.
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Old 08-10-2017, 03:37 PM
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And the "overhunting" hypothesis assumes accidental extinction--but what if the people back then decided for some reason that the megafauna were a pest ("Og tired of motherfucking mammoths on motherfucking plains!") and developed a deliberate policy of extermination?
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Old 08-10-2017, 04:15 PM
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The Passenger Pigeon would like to disagree. As would the Tasmanian Tiger and a bunch of others. And those only took a few tens of years. We're talking a timescale of centuries, and many fewer animals to begin with. I'm not saying it's true, just that it's not at all preposterous that humans can wipe out a species in a very short time.
Good point ... I should have qualified "neolithic humans" ...
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Old 08-10-2017, 04:19 PM
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Sauropods have hollow bones, which are much lighter per volume than any mammals. This is mitigated by denser mediums like saltwater oceans, so you can get things like the blue whale.

Are bats' wing bones much thinner than those of birds of comparable sizes? Even the larger ones like flying foxes?

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Old 08-10-2017, 05:45 PM
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Also, the largest ornithiscian (which lack air-sac and hollow bones) was shantungosaurus, which is comparable to the largest known land mammals.
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Old 08-10-2017, 06:11 PM
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Wow. I'm impressed.

EVERY SINGLE PERSON MISSED THE OBVIOUS AND ONLY CORRECT ANSWER.

Actually, the one that was closest was the joke answer about taxes.

Everyone is demonstrating a lack of understanding of evolution and how it ACTUALLY works. I never cease to be amazed that people get it wrong.

Here's the correct answer:

Q: Why are there no dinosaur sized land animals today?

A: Because there aren't.

That's it. Nothing has "changed."

Reasoning Hint: You know when ELSE there were no land animals the size of the larger dinosaurs?

Answer: Every OTHER of the millions of years they weren't here. As in BEFORE they were here.

Everyone seems to have forgotten that this planet spent millions upon millions of years, with creatures just a few cells in size or less. We didn't go from zero life, to dinosaurs, to asteroid strike, to humans, and then STOP.

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Old 08-10-2017, 06:57 PM
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That'd be a valid answer if there were only one species, or one set of closely-related species, of super-large dinosaur. But when you have a wide variety of different diverse species all reaching sizes much larger than the largest land mammals, you start to wonder why.
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Old 08-10-2017, 07:41 PM
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.. Presumably it's still possible for land animals to get that big... So why no giant beasts today?
It's pretty obvious to me the underlying question is if we know of any reasons that land animals that big can't exist anymore.
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Old 08-10-2017, 08:15 PM
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"Og tired of motherfucking mammoths on motherfucking plains!"
+1 internet
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Old 08-10-2017, 08:34 PM
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There are no dinosaur sized mammals because we ate them.

Okay, not really true, but at one time, something called megafauna mammals ruled the land all around the world and just happened to disappear about the same time humans started colonizing those areas.

Elephant type species use to be found all over the world, but quickly disappeared in Europe, most of Asia, and the Americas about the same time humans populated those areas. Other extremely large mammals like the giant sloths also disappeared at the same time.

Coincidence? Many biologists say there's simply not enough evidence. It could have been climate change that did them in. Many disappeared when there was a sudden warming or cooling of the local climate. When rainforests disappeared or reappeared. It could have been the climate.

And, it could have been because a creature suddenly showed up with a brain that looks at something really big and scary, and instead thinking "Wow, I better run and hide" thinks "Yup, I can eat that".

Dinosaurs took a long time to get to that XXXXXL size. We forget how long the dinosaurs lived. They started to evolve at the beginning of the Triassic era over 250 million years ago, dominated the Jurassic, and then onto Cretaceous before they disappeared a mere 66 million years ago. That's 180 million years of evolution -- three times the length mammals have been around. After 50 million years, one of the largest dinosaurs was the melanorosaur which grew to about 25 feet in length -- not quite twice the length of a mammoth. It took 100 million years of evolution to get to the brontosaurus which was over 75 feet long.

Mammals have had only had about 60 million years to evolve before we showed up and started eating them. Imagine how big mammals might get if they had 180 million years to evolve -- and how tasty they would be.
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Old 08-10-2017, 08:50 PM
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Wow. I'm impressed.

EVERY SINGLE PERSON MISSED THE OBVIOUS AND ONLY CORRECT ANSWER.

Actually, the one that was closest was the joke answer about taxes.

Everyone is demonstrating a lack of understanding of evolution and how it ACTUALLY works. I never cease to be amazed that people get it wrong.

Here's the correct answer:

Q: Why are there no dinosaur sized land animals today?

A: Because there aren't.

That's it. Nothing has "changed."
Emphasis added. Wrong.

The conditions on the earth today are not the same as those that existing ~100M years ago. Whether any of those conditions would cause animals to be smaller in max size today is debatable, but it the idea that "nothing has changed" is flat out wrong. As far as we can tell, for example, O2 levels have fluctuated significantly since the rise of that element in the atmosphere some 600M years ago.

Last edited by John Mace; 08-10-2017 at 08:50 PM.
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Old 08-10-2017, 09:25 PM
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That's it. Nothing has "changed."
Define Nothing?
once North America was divided into an East side and a West side, by an Ocean.
T-Rex live on the west island

South America had no overland Passage to North America.
Antarctica was a lovely sub tropical place and was not at the south pole.

Once there were ENORMOUS insects.
There are not now, and there could not be even if you were God's geneticist.
Why? Because something has definitely changed.

Many many many ancient animals could not even live on earth today, even if there were 0 humans, and God himself resurrected them.
Why? Because something HAS changed.

So, could we define nothing again?
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Old 08-10-2017, 09:31 PM
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Many many many ancient animals could not even live on earth today, even if there were 0 humans, and God himself resurrected them.
Why? Because something HAS changed.
OK, I'll bite. What changed?
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Old 08-10-2017, 09:37 PM
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First thing to consider is body heat. The Elephants of today have giant ears, for the express purpose of shedding heat (plus apparently they get hard of hearing in old age?). Since there's no evidence that dinosaurs had any similar heat-removal mechanisms, we need to conclude that although they may have had some heat-generation mechanisms (latest pet theories), they were generally not fully warm-blooded.

With warm-bloodedness, as alluded to, comes a host of other issues. The animal can still move well when the climate is cold, but also needs significantly more food and the protective mechanisms (fur or blubber or feathers) to preserve that heat in cold climates. So consider a croc or gator - a cold-blooded animal can grow from a tiny finger size to a dozen feet or more, and with minimal change of body morphology or adaptions (other than relying on a warm climate). A creature that starts off the size of a mouse and grows to twice the size of an elephant, warm-blooded, will have to go through a significant change in heat-adaption strategies. A body twice the dimension of an Elephant generates 8 times the heat with 4 times the surface area to shed that heat.

Another factor is brains. The human brain is the single biggest factor in our survival, despite the evidence of some specimens. Smart outdoes strong very often. The Jurassic may have been an arms race of size and armour, but the last 65 million years appears to have been a brain race.

I have read that the human brain consumes 30% of the body's calorie intake. To feed brain and size, any warm-blooded animal with a decent brain would have to eat a massive amount of food. Grazers like cows and such are non-stop feeding machines, since the nutritional value of grass is quite low - even when using bacteria to aid in converting cellulose for digestion.

But, warm-blooded predators are very active - so slow, ponderous, massive cold-blooded animals would not have the speed or smarts to avoid becoming a meal; ditto for their small-brained tiny offspring, before they have a chance to become large. Most surviving reptiles have occupied niches to marginal or complex for mammals - swamps and tidal shorelines, isolated islands, or moving in and out of water.

Mammals tend to have few offspring, and the larger the mammal, the longer the gestation and child-rearing cycle. Other than relatively primitive marsupials, offspring tend to be not that much smaller than adults by the time of their birth.

So to sum up - mammal morphology doesn't allow larger beasts for heat and food reasons. Smart, fast, active predators have killed off anything too big to get away, or picked off their young.

So what about mammoths? Read Darwin's account of the Galapagos. The first humans to get there found the birds, adapted to the isolated island, so unaware of the danger of humans that one passage describes a sailor pouring a glass of water, and a bird lands on his arm to start drinking it as it pours. A visitor a decade or two later describes a young boy with a 3-foot stick sitting near a watering hole, whacking birds and killing them for dinner. Another few decades or many bird generations later, and the surviving birds are as skittish as the mainland. The same applied to the dodo - too unaware to be frightened of humans, until it was too late. Mammoths would have been even worse. by the time a few generations of mammoths learned (were selected) instinctively to fear humans, there weren't any more generations.

This is the pattern everywhere outside of Africa and Eurasia - animals had to learn the hard way to fear humans. If numbers were too few and generations too long (or humans too mercenary) then sayonara. It wasn't that anyone decided to hunt them to extinction; just that every individual actor fed themselves in the most expedient way with powerful weapons developed to feed themselves when prey were much less cooperative; and a large prey would continue to not be aware of the danger of humans long after the smaller ones had evolved to figured out the run away, so they were targets of convenience.

As for elephants, they evolved alongside humans and so learned to avoid them before they had more lethal weapons of mammal destruction.
  #46  
Old 08-10-2017, 09:51 PM
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OK, I'll bite. What changed?
Simple but big ones
Food, Climate, Habitat

Where does one go to find forests of Lepidodendron to eat today, if that is what one eats?
How about Conifers like sequoia? Only a few in california.
Cycadeoidaceae? nada.
You can't live if the food you eat, that you adapted to digest does not exist.

And

Mega insects can no longer exist mostly for one simple fact (that i know of)
Oxygen levels.
Their breathing apparatus only supports X maximum size because of oxygen intake.
You need more oxygen % to grow bigger
After that its a limitation of the exoskeleton and circulatory iirc.
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Old 08-10-2017, 10:06 PM
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I have trouble imagining that pines constituted good food for anyone other than insects. Giant ferns, maybe.
  #48  
Old 08-10-2017, 10:06 PM
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md2000, last I heard, the prevailing wisdom was that Stegosaurus's plates served as heat radiators, much like elephant ears. Is that no longer accepted?
  #49  
Old 08-10-2017, 10:06 PM
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Originally Posted by Weisshund View Post
Simple but big ones
Food, Climate, Habitat

Where does one go to find forests of Lepidodendron to eat today, if that is what one eats?
How about Conifers like sequoia? Only a few in california.
Cycadeoidaceae? nada.
You can't live if the food you eat, that you adapted to digest does not exist.

And

Mega insects can no longer exist mostly for one simple fact (that i know of)
Oxygen levels.
Their breathing apparatus only supports X maximum size because of oxygen intake.
You need more oxygen % to grow bigger
After that its a limitation of the exoskeleton and circulatory iirc.
OK. Two questions:

1. Why was oxygen content of the atmosphere higher in the dinosaur era and why is is it lower now?

2. Why don't massive forests of the plants you mention exist any more?
  #50  
Old 08-10-2017, 10:17 PM
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First thing to consider is body heat. The Elephants of today have giant ears, for the express purpose of shedding heat (plus apparently they get hard of hearing in old age?). Since there's no evidence that dinosaurs had any similar heat-removal mechanisms, we need to conclude that although they may have had some heat-generation mechanisms (latest pet theories), they were generally not fully warm-blooded.
OK, let's just start here. African elephants have "oversized" ears. Asian elephants, not so much and their close relatives, Mammoths surely were not lacking of a heat dissipation organ while living through a Siberian winter.

And yes, there is evidence of heat dissipation in some dinosaurs. And since many birds use their legs to regulate heat, it's quite possible that some non-avian dinosaurs did, as well.

And what does it mean to be "fully warm blooded"? Scientists generally use the term endotherm and ectotherm. Birds are Endotherms as are mammals. There is no reason to think that other, non-avian dinosaurs were not also endotherms.
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