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?
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).
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.
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.
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.
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.
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 …
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.
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?
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?
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.
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.