ExtinctZoo - When The Amazon Was A Mega Lake

Episode Date: October 18, 2025

You’d never want to get lost in the Amazon, BUT you really really would not want to get lost in the Prehistoric Amazon, as it was a giant cesspit of absolute nopeness.

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Nature is beyond amazing and all around us. We got deserts, forests, rivers, mountains, oceans, the list is near endless. And while every habitat is breathtaking in its own way, there are those particular places that seem time and time again to captivate people more the normal. And there is perhaps no better example of this than the Amazon rainforest and river, sometimes collectively known as the Amazon Basin. This area is made up of extensive lush rainforests, swamps, and thousands of waterways, providing an abundance of resources, which allows for the existence of some of Earth's most unbelievable life. And its crazy nature has led to it often being touted as the last frontier on land. And this is further reflected by the fact

that a poll, with over 600 million votes, listed it as one of the seven new wonders of Earth. Impressive, and proof that nearly everyone knows about it. But that said, not all, or dare I say most, realize just how giant it truly is. The rainforest, for starters, is by far the largest in the planet, out competing the second place, Congo, by a magnitude of three. While the Amazon River is so expansive and powerful, that it moves water about six times faster than what's seen in any other river on Earth. In fact, you could combine the Nile, Mississippi, Congo, and you could combine the Nile, Mississippi,

Ganges, Thames, and Yangtze River, and still not beat the amount of water the Amazon is moving. And due to its sheer size, the Amazon in some ways seems eternal, and it's hard to imagine it ever being different. But yet, at one time, it was unrecognizable compared to now, and not just in how the actual landscape looked, but also in the sense of what called it home. As if you think the Amazon is scary today, then boy, oh boy, do I have news for you, because once upon a time and make its present-day self looks somewhat like a petting zoo,

and there is no scarier time in the Amazon's history when it was not a rainforest, but rather a super mega lake, now known as Lake Pabas. This bonkers realm is believed to have started forming long ago, about 21 million years, give or take, during the Aquitanian. This was the oldest age of the Miocene epoch, and it was generally defined as a dry and cool period. But clearly the Amazon didn't get the memo,

as it remained relatively warm and wet by most people's standards. The climate had a lot of say in how things operate in these parts. Yet, what was having a far larger impact on the area was the wax and waning of the lands, with tectonic activity causing the Andean Mountains to rise up. And their increased elevation eventually got to a point where the flow of water was heavily impacted, essentially creating a huge bowl in the West, in which water would get trapped. And thus the region rapidly began to flood and fill up to the brim with water, giving us the pay-boss systems.

Now, I did say this area was a super lake, yet the nuanced answer, is that we aren't too sure as to what exactly this region really looked like. We know it was wet, surely. However, the question is, was it one massive lake, multiple lake systems, or a giant marsh, or something in between? And that's where it gets hazy, with one of the more accepted hypothesis being that it was a mega wetland, with loads of varying environments. Whatever the case, though, you would have found a lot of water here, as the Lake Pabas

system at its peak was larger than present-day Japan, and in certain areas could achieve depths of 50 meters or 150 feet. So for people with classophobia, this is rather unwelcome news, and this certainly wasn't helped by the fact that what lived in these waters consisted of what I would tentatively dub non-human-friendly life. And honestly, gave the Western Interior Sea, i.e., the Earth's deadliest sea, a run for its money. Because if I had to choose across either one, I'm not exactly sure which one I would choose, which is saying something. Additionally, like the Western Interior Seaway, the pay-buss mega wetland had phases to it, some of which were more chill and others more, Nope. And there is a clear time when it reached the peak nopeness, which was the middle mycine. This was a very important part in Earth's natural history as a whole. Yet, it was really an

event in the midst of this age that mattered the most, the MMCO, where the middle mycine climactic optimum, an interval where in temperatures worldwide rose, with the average temp being about 3 to 4 degrees Celsius warmer than the present, which for perspective would be kind of like going from Portugal to Syria. And based on present measurements, Lake Pabas would have been comparable to the top five current hottest countries. So you definitely want to bring some refreshment and a lot of sunscreen. This heat wave is believed to have stemmed from an elevation in atmospheric carbon dioxide. It might have also fed the vegetation of Pabas, resulting in giant trees, oversized marshes, thick mangroves, the lot, while also leading to the largest size

for Lake Pabas in terms of maximum reach and water levels. And unsurprisingly, this allowed for an abundance of life to seep in, and cold-blooded animals in particular took a heavy liking to the new heat, which helped not only their diversity levels, but also their sizes. And though the Sinozoic as a whole is often called the age of mammals, Lake Pabos was definitely in place ruled by reptiles. Yet, despite each group of Scaly's reaping the rewards, so to speak, it was one group in particular that took over, good old crocs. And if you thought Australia, the Everglades, or the Nile, has a crock problem,

think again, as the Paboss put them to absolute shame, with formations linked to the wetland, indicating a higher diversity seen in crocodilians than even birds. In other words, imagine a place where seeing a bird is more of a rarity than seeing a crock, which I don't know about you guys, but to me, it's probably not the kind of location I want to visit. And due to the high number of crocodilians living in Pabas, we see that there were many types, with niche partitioning being routinely observed. Along with heavy diversity in niche partitioning, of course, comes great differences of size.

And while a few remained within what we consider the normal limits, a handful evolved into supersized giants, and this included the king of the mega wetland, and what was the largest came in and possibly the biggest crocodile to ever live, the purasaurus. There are no words that capture just how monstrous this behemoth was, but I will try. The first report of its existence comes from 1892, when skull material was located in the porous region, by a team of paleontologists, and the sizes of these skull pieces were nigh unbelievable, And they instantly knew this was something different, so to speak. In subsequent discoveries and more material only confirmed this, as what it unveiled was

the supercrock that was built like a tank and it proportions off the charts, with the skulls alone measuring 4.7 feet or about 1.5 meters, and being almost comically robust at that, taking on a rather box-like shape. And so clearly from this powerful head alone, the perosaurus was top dog and Pabas, and a vicious predator at that. Although its post-cranial size, the body size, is something that not everyone agrees on, as post-cranial bones have been rather elusive. But most studies have found that at the very least, they would have measured 9.2 meters or 30 feet long, and weighed over 6 tons, which already greatly exceeds the largest reptiles of today, and puts it on par with literal

killer whales. But I have to warn you, things only get crazier after this, as these are the more, quote-unquote, conservative estimates. Other studies have reported theoretical maximum, from 33 to 42, or even 52 feet, or 12.5, 10, and 15.8 meters, respectively. Additionally, at these bigger sizes, the weight also balloons, and it's possible that the largest adults weighed between 8.4 and 12.6 tons, which at the latter weight, we are talking about a crocodilian heavier than even a mink whale. If true, it would also make the Purosaurus the heaviest crocodilian ever, and though the accuracy of these estimates are kind of hard to assess,

separate studies do suggest a high likelihood, that the parasaurus was indeed heavier than the most famous megacrocks, like the dynosucas or sarcosucas. And given its titanic broad jaws, it would have required a massive neck to support it, not to mention a muscular robust body as well. And given the absurd nature of its jaws, you know this guy had one mean bite, with models implying a bite force of up to 69,000 neutins, which sounds a lot, and it is, with very few animals having achieved anything even close to this, not even the infamous T-Rex. And at this bite force, it would essentially be like having a cargo truck dropped on top of you.

But instead of tires crushing you, the damage was delivered by dozens of 2-inch or 5-centmeter long teeth that were curved, covered in two cutting edges, and thickly conical, allowing for tremendous bites straight onto bone without harming these teeth at all. And due to their shape and design of the skull, it's clear that Peresaurus was a hunter of large vertebrates, who utilized puncturing and holding bites to debilitate and capture prey. And these stats alone make Perosaurus one deadly killer, but things only get worse for the rest of Pabas, as paleontas reckon that despite its massive weight, this guy retained the classical finishing move seen in many crocodilians. In other words, the death roll. This brutal move is designed

to not only subdue, but literally dismember prey, and with modern crocodiles, has been known to rip animals as large as buffaloes, to pieces. So I don't want to imagine just how messy a death roll from the Perosaurus would have been. And thus naturally, this reptile was clearly the apex predator, and nothing else we know from the region would be safe from a fully grown one, which is why it's also so unfair that Perosaurus had impeccable defenses as well, being covered in thick scales and osteoderms far greater than the armor seen in any of its ascendance, and keeping it well protected from many animals or from its environment, as the waters of Pabas likely were riddled with fallen trees and various debris that could be pointy.

And ultimately, the perisaurus found extreme success with this build, as fossil remains show that it was not concentrated to specific environments within Pabas, but instead lived throughout the entire thing, inhabiting rivers, floodplains, and lake environments. And so, if you saw water run and you were in said, water, well, it was nice knowing you. But while Purosaurus was to the Pabas formation what the T-Rex was to Hell Creek, it was by no means the sole crocodilian, nor was it even the only giant one. And a testament to this is that the Pabas was also home to possibly the largest Givialid ever. This family is currently only represented by the garrials and false garrials. But in ancient Pabos, there was a whole lot more, including Griposucas.

Now, I'd much rather swim into this guy than a perisaurus, but to be honest, I'd prefer neither, as this guy was still a giant within its own right. Thus far, four species of this genus has been discovered, and the largest by good margin is the Griposucas Croyzati, a species described in 2009 who seems to have been stuck in the northern tip of Pabas, possibly frequenting both freshwater and coastal environments, giving it access to a diverse range of food, which clearly did wonders for the northern tip of the baybos, who seems to be its size, as estimates over 10 meters, or 33 feet long, are very common for matured individuals. Only the rampasusus at the same family rivals it entitled for the largest gavialid.

In seeing this, it's pretty evident that Gripasukas did not have many foes either, rather just a lot of victims. Though I will say, none were probably as large as the prey perisaurus was going for. Since, opposite to the perisorosis's broad school, Griposuchus had evolved an extremely narrow and slender one, leading to a theorized diet, heavy and large fish. But given his sheer size, it's quite realistic that the occasional mammal might have been on the menu too. And if this duo of Titans didn't seem like enough, there was also a third stupidly huge crock that completed the Pabas trifecta and its name the Morosuccas. Like Perosaurus, it too was the type of Kaman, yet these siblings couldn't have been

more opposite, with this genus in some ways being closer to ducks, as it's sported at a broad, flat and elongated skull that is often described as being duck-like. Sounds funny, but I'd probably never say that to its face, considering that adults in this genus could reach 9.5 meters or 31 feet long, and weigh in excess of four tons. So basically four giraffes mashed together. And because of this stature plus its odd face, there has been great interest in this mysterious creature's diet, with three main hypotheses having been proposed. The first is that it was a generalist eater that patiently waited for animals to drift into its wading mouth, where it would then swallow them whole. The second option

was then at a twist, this crock was really a gentle giant, who fed on floating plant material. though to be honest, most are not putting their bets on this idea, with a majority support, instead go into the last hypothesis, which is that, use its large duck-like mouth to sift through the muddy floors of rivers and lakes, in order to uproot and consume a mix of vertebrates, mollusks, crustaceans, and fish. And while it may not be as voracious as its other two massive relatives, swimming into one would still not have been good for your heart. This, I guarantee.

And just remember, while these three were the true giants of Hayboss's water, there were still plenty of other crocodilians to go around, with fossil formations revealing the presence of at least a dozen other genera that again demonstrated a wide range in size, and you would have found multiple kinds that rival the largest crocodilians of today, whilst there was also a handful of much smaller genera, there were in some cases dog-sized or even smaller. And that might sound good, but what this really means is that every animal in Pabas had a crock designed to hunt them. But as Ian Malcolm so beautifully put it, life finds a way.

And co-existing creatures put up a good fight against these tyrants, using some of that good old gigantism right back at them, which is why this area also became home to a lot of large fish, including Potamo Trigon that rivaled the heaviest freshwater stingrays on record, and multiple croakers and drums that were human-sized. Yet, the animal that would likely turn the most heads in these waters, which wasn't a crock, was actually a turtle, though I frankly think calling it a kaiju makes a bit more sense, because it was the biggest freshwater turtle of all time, and one of the biggest, period, the stupendomis.

And don't want this name confuse you as it has nothing to do with being stupid, besides perhaps your expression when seeing one, but 100% to do with it being stupendous, which is what sums up this reptile, who even gave the likes of the Arcalon a run for its money, as its carapace alone was in some cases 2.86 meters or 9.4 feet. And remember, this was the shell, not the entire body. So it comes as no surprise that it was,

also quite hefty, being over one ton. And it's possible that these extreme proportions were essentially forced upon the turtles by the threat that Crocs posed. And the enormous shell would have certainly come in handy when traversing these waters. And we even have direct evidence of this, as multiple specimens from Pabas have been found with bite marks in their carapace, as well as actual embedded teeth that were crocodilian in nature. Now, I expect that not every turtle was this fortunate, but at least in these cases, it seems like the XXL shells did the trick, helping their would-be victims survive and fight another day. Now, I don't know about you guys, but seeing a mega-sized turtle would certainly check a few time-traveling boxes for me.

But this is one flippered animal you definitely would want to observe only from a safe distance away, as well we generally think of turtles as being harmless, cute creatures, for the most part. The stupendomis was a feisty guy. It possessed a hunkering beak that was curved in hard, allowing it to snip and crunch various items, likely resulting in a durofagous omnivorous diet that was rather generalistic in nature. And given its size, fish, mollusks, smaller crocodilians, and snakes were all likely game. And the defiance to their crocodilian rulers among the turtles did not end its stupendomis either, as another large-bodied genus lived alongside it, the caninamus.

It was a smaller genus than stupendomis that was somewhat similar in size to leather-backed sea turtles. So, not massive-massive, but still definitely not pet-sized, and it would have been even less optimal for house living considering its bad temper, since cononymous was highly aggressive and carnivorous. This notion stems from its hooked jaw that it was stout, robust, and had curves along it similar to what's seen in the alligator snapping turtle.

And thus the belief is that this was just one big old snapping turtle. Albeit, opposed to the risk of losing a hand, you'd be at risk of losing your entire legs, arms, and maybe even head from a bite. And I likely felt on anything it found, except for perhaps giant crocodilians. But who knows, perhaps it tried. And so, when even the turtles are unhinged, you know a place is messed up. But don't forget, you also had the usual nightmare suspects.

In other words, sharks. Now granted, these cartilaginous fish seem to have been extremely rare in the Pabas overall and limited to the regions closer to the coasts that were likely brackish and exposed to periodic marine incursions, which are known to certainly have happened. And so this was just one more thing to worry about. And this is why it's seriously impressive that aquatic mammals managed to show up here in any out, despite their relatively cold-blooded onslaught, with the two main mammalian groups in the Pabos waters being Sirenians and River Dolphins. At least multiple species of each coexisted with

the reptiles and fish, and like those groups, also ranged in size. For the Sirenians, they could be quote-unquote fun-sized all the way to the sizes seen in the extant manatees, while the dolphins, on the other hand tended to swing larger and actually got in on that good old gigantism from time to time, as it was here that the biggest river dolphin of all time lived. The Pabasas'bos and the Today, that title for the largest river dolphin goes to the Amazonian River Dolphin, that coincidentally lived in a corresponding area, and whose adults measure up to 8.5 feet and way about the same size as a gorilla, which is respectable, yet it has to beef up a bit more if it wants to catch up to the Pavanista, who is about 30 to 35 percent larger, on average.

And similar to the other inhabitants in the Pabas, the Pabonista also became a bit more menacing than its living relatives, and we know this thanks to the unique construction of its skull, which compared to extant river dolphins was unusually sturdy and sported relatively longer and thicker teeth. What's more is that its snout was oddly elongated, yet it wouldn't have been flimsy or fragile, instead being sturdy and capable of enduring high stresses due to the robustness of its overall skull. And then on top of that, the post-cranial skeleton featured many attachment points for muscles. So in other words, we had a dolphin chad on our hands. And paleontologists do agree that the Pabanista practiced a reptorial lifestyle

that was supported by the cetacean's hallmark opiability, echolocation. which would have proved wonders for Pabanista, as the development, or rather reduction in their eyes, reflected the PAYBOS was mainly composed of highly muddied waters, where visibility was very low, and thus things like echolocation would have been phenomenally useful. And that is this fact that really gives me the hebi-jee-jee-bees, that fact being that the Paboss was essentially a giant murky swamp. Imagine that for a second. You can be just minding your own business, paddling out on a little canoe,

and peer over the side and see absolutely nada, just a dark abyssed. While unbeknown sea you, multiple predators over one ton could be lurking just an arms reach beneath you. Yeah, no thank you. Here's the problem, though. Staying away from the water is not a foolproof plan to survive in the prehistoric Amazon, as the land was also home to its own nightmares as well. From formation sediment, it seems like the majority of vegetation and habitats in the system, plus its immediate surroundings, was a mix of rainforest, palm swamps, normal swamps,

ferns, and open flooded areas where aquatic plants are abundant. And this might sound lush and picturesque, but don't be fooled. All this vegetation did was make it easier for terrestrial scurries to hide. And in Pabas, there were two families of particular that were essential to keep an eye out for, the Sebikids and Forest Rackids. Both of these groups were like the biggest terrors in the water, i.e. reptiles, kind of. So again, so much for the age of mammals. But I guarantee you that you would not be mixing these two up.

For the Sabakids were a group of typically large, ferocious crock-like crocodile more, who hunted utilizing powerful skulls, jaws, and teeth, which were actually more similar to those of giant meat-eating theropods than two other crocodilians. Oh, and they also had long limbs, allowing them to run. Yeah, run. And unlike what we've been programmed to believe about crocodilomorphs, these guys were completely terrestrial.

So in other words, they probably ran fast at that. And then you had the forest rackets, or the terabirds. So, suddenly reptiles, in a sense. who were, as the nickname suggests, predatory birds, albeit flightless ones. But we're a bit too oversized to be confused for a chicken, and like the same type of teeth as seen in subicids, but still were able to kill plenty thanks to their exceedingly durable, sharp-curved beaks. As well as their long legs, they're granted them immense speeds while chasing down prey. So imagine Roadrunner, but multiplies deadliness by a hundred.

Now, both the terror birds and subicids were not new news in prehistoric South America, as well before the payboss system, they were around. Yet, the wetlands really brought out the worst in them, Because it was in the pay bus that the largest of each of these families lurked. For the Sebuchadis, this was the infamous Burinusukas, an animal who needs little introduction, and the adults could reach 7.5 meters or 25 feet long. In other words, greater than the length seen in the longest modern crocodilians. And just to remind you again, these guys are running, not swimming.

Which is only more impressive when you consider that they also weighed about two tons, thanks to their built and armor. And to make matters worse, there are even more extreme estimates, which suggests that 10 meters or 33, three feet was also within the realm of possibility, which would be like stacking three rhinos standing back to back. Now, I will say, subsequent studies have typically stated lower estimates, but in either case, the Burinusukas remains the largest known sub-a-kid, as well as a very strong contender for the biggest land predator to have ever lived since the freaking dinosaurs. Talk about an achievement. And so given this, the Brinausucas did obviously blow away the competing terrobirds in the wetlands. Yet, the birds did muster respectable fight, as recovered bones

in the region showed what is among the largest terrabird ever. A for now unidentified species that would have stood at 2.5 meters or over 8 feet, making it not only taller than the likes of shack, but also one of the tallest birds of all time. And given its vertical exceptionality, this bird would have been a hefty fellow too, weighing around the same as a lion. And for me, this would make me want to skip seeing this guy on a time-trophication. But for others in Pabas, their size just made them more appetizing, despite the fact that they were also terrestrial apex predators, as terabird bones have been found riddled in bite marks, indicating that it became someone's KFC.

And the culprit, our old pals, the Megacrocks. So yeah, I think we're going to have to take our chances on land. And yet, they still are not good odds. For beyond the larger subicids and terrobirds, you also had the smaller, more diverse members, too, such as the Lankstonia and multiple unidentified terabirds, plus some unwelcomed faces that are still present in the Amazon, namely a variety of boa constrictors. So with all this said, this error is without a doubt exceedingly unhinged, even for a prehistoric environment. I mean, think about it. In one spot, you could find the largest river dolphin, turtles, Cayman, Gavilid, and land predators since the dinosaurs, all in one spot.

Most places would be considered crazy for just having one of these things, let alone all of them. And given this, it's seriously impressive that besides terrifying predators, herbivores existed too, and were unsurprisingly the most widespread animals in these part, represented by none other. than us. Well, mammals. In the waters, our diversity wasn't exactly the most impressive, even making the extent mammals in the Amazon seem rather mundane and boring. For instance, today one of the otter creatures in the Amazon is the Capybarra, the biggest living rodent on earth, which loves swimming, lives by the water, and is actually semi-aquatic. So pretty interesting. But back in the middle Miocene, these guys had not yet come along. But in their place were other

rodents, including in Pabas, the faux beramus, a grass grazer who is a relative of a modern-day guinea pig. But that's where the similarity stops, as it cannot be farther from them in size, being more similar in that department to polar bears, making it among the largest rodents of all time. Meanwhile, the Pabas system would have been home to an absurd amount of ground slots, too. A group of unfortunately now-exing slots that were far more agile, active, and terrestrial than living ones, and it also tended to be more unusual in stature. In Pabas, their level of diversity was off the charts. We are aware of at least 10 different genera they call this place home,

and would have offered the perfect mount lineup. For across the bunch, there are species akin in size large dogs, pigs, deer, and even elephants, at least Asian elephants. As the ground sloth, Euramaquia, is believed to have weighed up to four tons. In addition, one-plus tonneo-unculates would have been a common sight as well, plus animals as superfisher resembled bisones and rhinos, but just lacked horns. Then moving on to some of the more funky-looking life, you also have a mix of glypidons, like topterna, and, of course, ant-eaters,

who are actually deceitfully large, and hard to miss, given their highly elongated tongues, strange eating manners, and highly modified schools that honestly looked like they're missing apart. And if you think you can't take any more new animals, then hold on to your horses, because I can't let you go without mentioning that primitive primates, bats, astrapatheria, metatherians, and chiroptura, were all out in this mega wetland, repping us mammals as well. So by now you should have gotten the memo that Lake Paboss was one heck of a place, and maybe a tad bit too much for nature to handle.

It's obviously many walks of life I just mentioned do not exist anymore, nor is obviously the mega wetland. So what exactly happened? How does such an expansive environment disappear? Well, just like the Andes giveth, so do they takeeth. And during this whole time they kept rising up and up and up, eventually reaching a point where instead of flooding the area like a bull, the bull started leaking water out, and the area slowly started to drain, causing immense shifts in the environments that forced animals to move out

or disappear. At some point, this uplift of land even ended up blood. blocking what is now known as the Amazon River from flowing into the Pacific, a venture resulting in its flow to do a complete shift. So yes, at one point this iconic river didn't even run the same way as it does now. And over enough time, the Pabas system fully emptied out, until the only remaining water became the Amazon and its tributaries, which have remained to this day.

But of course, many of the amazing and terrifying animals that called the system home are no more, but perhaps for the best. Thanks for watching, and until next time, on Extinct Zoo.