Chapter 1: What were the largest animals to ever walk the Earth?
Over the four billion years of life on the speck of dust we call home, the Earth has seen countless walks of life come and go. And many of these groups have been wondrous and large within their own rights, but only one group can hold a title as the largest. And when it comes to walking, at least, there is one clear winner. And that would be, of course, the dinosaurs.
a diverse group of reptiles that came in just about every shape and size over their record-long rule, with many of them holding various size records as well. And yet, even amongst them, there was one group that stuck out like a sore giant thumb when it came to stature, being the biggest animals to ever walk, period. And that would be, obviously, the sauropods.
First appearing in the very late Triassic period just over 200 million years ago, this group of longnecks ended up becoming one of the most successful animals to ever live, spreading out across the entire world, touching every single continent, and reaching sizes that were once thought to be impossible for terrestrial animals, with some of the largest members possibly even surpassing 100 tons in weight, which is for reference like 20 stegosauruses smashed together into just one super animal.
And because they were so large, we have a fairly good understanding and record of them, as the larger a bone is, the larger the chance technically it has at fossilizing, which is why we have something called a preservation bias, which in short means an organism, or group, preserves relatively better than others.
And this partially explains why in some places, there are so many gosh darn giant sauropods, like the Morrison Formation. And such formations where dozens of sauropods live also go to show just how successful the group was, with many considering them the most dominant herbivores of the entire Jurassic.
So here you have these extremely successful giants that are literally everywhere and preserved quite nicely, but then suddenly during the Cretaceous' Cenomanian stage, about 100 million years ago, they suddenly disappear, just like that.
And this wasn't a slow vanishing, rather a pretty abrupt disappearance that would strangely last for millions of years, until one day at the tail end of the Cretaceous, they would just suddenly pop up once more, creating one of the most mysterious periods in paleontology that is now referred to as the sauropod hiatus. However, here's the real perplexing thing about the disappearance of sauropods.
It was not a global phenomenon, only occurring in certain places, namely North America and Europe. Whereas on the flip side, in continents such as South America, Africa, and Asia, we see that the giant longnecks continue their reign, being undisturbed by the whole event. Which obviously leads to the second question of why was only parts of the planet impacted, while others were not?
Especially since the impacted areas seem to be far apart. It's almost as if one day, every sauropod past a certain line vanished. But again, why? And to answer this, it's best to start before any signs of trouble begin. So in other words, the late Jurassic.
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Chapter 2: Why did sauropods experience a sudden disappearance?
with the group only making a reappearance during the final Maestrichtian stage about 68 million years ago, so almost 30 million years since they had vanished.
And to just illustrate how long this disappearance really is, we are talking about a gap that's 1500 times longer than what you'd think to be the Ice Age, i.e., you know, that time of the classic mammoths, humans with clubs and fur, saber-toothed, etc. But while the Longnecks had returned, they never did achieve their old glory, as it was primarily just one sauropod that returned.
Remember the Alamosaurus, a rather giant titanosaur that might have been between 30 and 80 tons, which if true would make it fairly equal in size to the Argentinosaurus. So, a pretty strong comeback regardless, and ironically makes it the largest sauropod to ever live in North America, despite also being the last.
So far, its remains have only been found in southwestern United States, and it is believed to have migrated upwards from South America at the start of the age. The question is, though, why did they come back all of a sudden? I mean, dinosaurs were still around, and were arguably even better off than before.
And so, the answer might have had to do something with the original problem, the Western Interior Seaway. In the tens of millions of years after its formation, the inland sea had already drastically shrunk, increasing the map size, so to speak, once more, and allowing for more animals to squeeze in without the worry of extreme competition.
And similarly in Europe, it seems that just like the problem, the solution to the hiatus was similar as well, as worldwide there was a major marine regression and sea levels plummeted, and thus increasing the overall land size of Europe and also making it more accessible to the rest of the world.
And while this next part is more debated, the best hypothesis at the moment is that the sauropods' big break in Europe came from migrating titanosaurs out of Africa, who successfully set up shop in Europe once again, and even led to a partial resurgence in sauropod diversity, as multiple sauropods ended up evolving, such as Ampelosaurus, Lohueka Titan, Abductosaurus, and Petrus Titan.
Interestingly though, unlike the Alamosaurus, the new sauropods in Europe often were on the smaller side. perhaps as a reflection of insular dwarfism. And we've even seen in certain places, like Katzig Island, the smallest sauropods to ever evolve, that were legitimately closer to human size than they were to their giant relatives.
And so, with the hiatus officially at close, and the sauropods back in the north once more where they belong, the future for these giants was looking bright, with countless possibilities on the horizon.
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