ExtinctZoo - The Last Time Earth Was Iceless

Episode Date: July 12, 2025

Warm breeze, palm trees, and good ol crocodiles, just some of the things you might imagine when picturing a tropical paradise, and yet I am talking about Antartica, confused? Well, I am not talking about it now but as it was millions of years ago, when earth was completely iceless, and let me tell you this is just the tip of the iceberg, pun intended

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At First Citizens Bank, we roll with your goals, because we're built for what you're building. Fit for your ambition for Citizens Bank. Of all the prehistoric periods and events, there is perhaps none as iconic as the Ice Age. From it, we got things like mammoths, Smilodons, a never-ending amount of animals that have cave in their name, and of course, giant ice sheets. And thanks to mainstream media, it's also become a highly mythicized period. given just how different it was in the present. However, the truth is that we never actually fully left the ice age, at least according to glaciology, with an ice age referring to any time where an extensive ice sheets are present in both the northern and southern hemispheres.

And the world today still checks these boxes, at least for now. And there are also even looser definitions, where some consider an ice age to simply be any point when Earth possesses permanent glaciers or ice sheets anywhere. And officially, according to scientists, the present is still considered to be a part of the quaternary glaciation event. And obviously, many don't know we are still in an ice age, with people generally believing that Earth has pretty much always had large amounts of ice covering the planet. But that's actually not the case, and at various points in our planet's history, it has been completely iceless, which begs the question, when was Earth last fully green, or at least not icy. Now, you'd think the answer would

have something to do with the quaternary glaciation period, which is thought to have begun about 2.58 million years ago. But if you traveled a day or even a few years before this event began, you'd still find plenty of ice and coldness to go around, because this event is really just the tip of the iceberg, no pun intended. In fact, if you go back 1 million, 2 million, or even 10 million years ago, you're still going to find some parts of the planet covered in ice. No, to see the Earth completely iceless, you'd have to go back way farther than you'd expect. Before humans, or any of the great apes were a thing, a time when crocodiles lived in Antarctica. When palm trees grew in places like Alaska, mammals seemed alien-like, and continents were flooded

by oceans. In other words, the late Eocene. This was a mysterious time, which played out between 40 and 34 million years ago, meaning that the last time we had a green earth, we were closer in time to literal dinosaurs than we were to the present. In seeing that there was no permanent ice, you can bet that this bygone era was a lot hotter than things are today. With most studies finding that right before the ice age popped off, average temperatures

are about 5 to 8 degrees Celsius hotter than things are today, meaning that a country like France felt more like Syria, and that Europe as a whole was closer to being subtropical than temperate. Meanwhile, if you lived in, say, the U.S., you'd find the climate was more like that of Uruguay. And so naturally, if the climate is this different, other things are bound to be too, such as the kind of weather patterns you'd expect, with this time being much more susceptible to wildfires, powerful storms, heat waves, and uneven rain and droughts, helping to keep a key to the late Eocene and its inhabitants on their toes. But what was really the most noticeable change was the water, specifically how much more of it there was. You see, in today's day and

age, 70% of all Earth's fresh water is frozen as ice, which equates to about 2% of the total water supply. And sure, this might not sound like a whole lot, but its significance was easily seen in the Eocene sea levels, which were possibly 70 meters or 230 feet above current levels, meaning that maps at the time would have had a few changes. For starters, much of our current coast were submerged, and then on top of that, you add things like the entirety of Florida being snugly underwater, Europe being chiseled into the giant and small islands, India off doing its own thing, and the Sahara was wet, not dry.

And you can bet with all these water environments and warmer temperatures that the fishing was or would have been good, yet at the same time exceedingly dangerous, as it was in these waters that Earth's ultimate predetermined. predators of the time were lurking. And if you know anything about the waters of the Eocene, you probably won't be surprised to hear that this included the bacillosaurus, a very important animal at this time, as it, or rather its family, were the top predators of Earth that I was referring to.

Simply put, these guys are a now extinct group of cetaceans, or whales. But they were not like the whales who are familiar with today, as they were the complete opposite of gentle giants, being hyper-preditorial, having highly developed, mean-looking as well streamlined bodies and powerful jaws that frankly gave some of them appearances closer to mosasors than other whales Which may also explain why this group was actually first misidentified as marine reptiles instead of mammals And besides having the perfect builds for killing there were also other problems with this bunch First there were the prehistoric equivalent to mr worldwide seeing that the bacillosauridae managed to expand into every single continent on earth Antarctica concluded and they managed to do this concurrently meaning

if you ever found yourself in a late Eocene ocean or sea, you'd be almost guaranteed to swim into one of them if you stuck around long enough. Also, it wasn't just that they were found in each continent, but virtually every saltwater environment as well, including open oceans, shallow inland seas, and in some cases even brackish ecosystems like marshes and mangrove forests. And we know this from fossilized remains of multiple genera, like of course the bacillosaurus, but also Dorodon, Saghasidis, and Stramarius, that together conquered regions even consisting of places like the literal Sahar Desert. So this all-reaching influence was the first problem, but then you had the second one, which was the fact that these guys came in virtually every shape and size you could think of,

rendering nearly every animal around them a potential target. At the lower end, you had Tut Cetus, who was, by the way, named after King Tut, and despite being the smallest, was still very much bigger than all of us, measuring over 2.4 meters or 8 feet long, and weighing the same as a large bull shark. So not great news for human-sized animals. And then, on the complete opposite side of the spectrum, you had the parasitis. Now, there's a fair chance you've heard of this guy before, seeing that for a bit, it was actually considered a potential candidate for the largest animal, and not just of its time, but of all time,

with initial estimates giving it a weight of 340 tons, which just to put that into perspective would be like smashing together seven tanks, and then giving it a tail. And the crazy thing is that it wasn't actually that long, being only 20 meters or 65.6 feet, meaning that it was closer in length to a whale shark than to a blue whale, so a very serious chunkster. Now this being said, it has turned out that these original estimates were way off, but it is still the largest bacillus sororidae, and animal at that from the entire Eocene, with estimates now standing around 35 to 50 tons.

And ironically, despite being the biggest, it was also likely that, the friendliest, at least to larger animals. As due to its chunky nature, the parasitis was actually quite slow and unable to move freely, most likely having trouble adjusting its depth, and therefore probably spending most of its life in shallow water feasting on benthic animals, instead of being a giant killer. Although, even with parasitis out of the way, there was indeed another bacillosauridae who was both huge and bloodthirsty, and that was of course the bacillosaurus, who measured up to 18 meters or 60 feet long. So think humpback whale just 10 times scarier and streamlined, with its weight being about 15 tons, while also being an absolute speedster,

allowing for a very active hunting lifestyle, where the bacillosaurus fed on virtually anything it wanted, including sharks, large fish, and other marine mammals, including its own kind, such of the Dorodon. A fact we know, based off of stomach contents and preserved bite marks on multiple different Dordon specimens, with most studies even finding that other whales were actually this creature's main food source. And so obviously, considering that it hunted whales, it would have needed quite the bite. And let's just say it had one, having a chomp that registered some 20,000 newtons, which is enough, by the way, to shatter concrete under the right conditions. And this bite force would have been delivered through dozens of giant teeth that came in many different types, but could

overall be described as sharp, robust, and pointed, allowing it to pierce, crush, and then chew, yes, chew, their prey into paste. And so with all these traits combined, it's not surprising that this beast was able to hold quite the range, being found in North Africa, North America, and various parts of Asia. Now, the Bacillosauridae were ultimately a big part of what set iceless Earth apart, but they are for sure not the only lost relics from the time, for other oddities and monstrosities called the water's home. And this, of course, included multiple sharks, including one very peculiar genus, which is named the odotus.

Now this might not ring a bell for you, but the otadus is actually the very same genus which gave rise to the megalodon, albeit the megalon's time would have to wait a bit, as it had yet to evolve. Instead, the species of odotis swimming around was the arachylaidus, a shark that was giant within its own right, being capable of growing to 9.5 meters or 31 feet long, making it comparable to the biggest killer whales on record. And considering that, it probably won't be shocking to hear then that this Jaws was yet another apex predator of the time, who utilized a giant mouth and razor-sharp teeth to shred animals into pieces.

And this ferocity in size allowed it to enjoy quite the global range, just like the Bacillosaurus, being found in Europe, the U.S., Asia, and even Antarctica. And then just as a cherry on top, there's even a good chance that there was another odious species lurking around as well, an even bigger one at that, the obelicus, which in some cases could crack 12 meters or 39 feet, making it more comparable not to killer whales, but to large whale sharks. In other words, you'd probably want to bring a bucket of popcorn with you to the late Eocene, as giant sharks versus giant predatory whales probably went down at least once

or twice. And though there are many ways changed, sharks and whales today are still doing just fine. But not everything that was around back then has fared so well, and perhaps for the better, as the late Diocese's warmer temperatures supported many other creepy creatures as well, but one perhaps more than others, namely giant sea serpents. Now yes, we have sea snakes today, but thankfully they are not huge, nor are they too interested in us. But during the late Dio scene, I don't know if you could have said the same thing, as back then they were absolute units, best demonstrated by the Paleofidae, an entire family of extinct marine snakes that were uncomfortably large, as in the largest water snakes of all time.

The two biggest were Teres Venus and Paleophis, with the former having been the smaller of the two, measuring 5.7 meters or 19 feet, which already makes it on par with some of the largest snakes of today. And ironically, it was still tiny compared to its relative, Paleophis. which based off of vertebrae could reach a staggering 12.3 meters or 40 feet long. In other words, four times longer than any sea snake alive now, and awfully close to the size of Titaniboa, the largest snake of all time. And for now, it's actually considered to be the third largest identified snake ever. And despite their size, the paleofidae weren't just some lumbering giants.

They were highly capable of swimmers with large compressed tails that acted like tail flukes and would have swam through the water with an undulating movement, just like present-day sea snakes. But what's a bit strange and discomforting about them is that they were much more robust and powerfully built than what you'd expect from an aquatic sea snake. Leading paleontologists to believe that the paleofidae would have needed to rely on stealth and ambushes to strike large unsuspecting prey who they then would have killed with remarkably powerful jaws and hyper-flexible mouths that allowed them to swallow things whole, such as sharks, fish, and possibly even small whales.

And unsurprisingly, giant extinct snakes can do pretty well for themselves. And along with being apex predators, they too, like the sharks and whales, were found globally, which can also be partially attributed to, the warmer temperatures that gave them access to areas that nowadays would typically be too cold. And rendering late Eocene waters something to be avoided entirely. Now, luckily, with all this said, the conditions of Earth before ice did not just create monstrosities. As worldwide, other more friendly groups were benefiting from the conditions, as well, which included not only a variety of sea turtles, cephalopods, bony fish, and invertebrates, but also our favorite mermaids, cyrenians, who at this time were exceptionally diverse,

while also being a bit different than how we think of cyrenians now, as these guys were a bit more primitive, only recently having transitioned to a fully aquatic lifestyle, and resulting in a few kinds still possessing physical traits which you would not expect to find on an aquatic animal. I'm talking four limbs and fingers. In fact, there's even a chance that back then you could have spotted a sirenian walking about on land too, as during the Eocene not all had made a full shift to water yet, with some instead being amphibious, or in some cases, even primarily terrestrial. And they weren't only ones caught in this figurative middle ground, as another group doing

something similar was our old pals, the cetaceans. Since in conjunction to the bacillosauridae, you also had the protocetidae, a diverse group of whales that in some ways actually had more things in common with amphibians than their extinct relatives, seeing that they were, well, amphibious, possessing strong limbs that were developed enough to have supported their bodies on land, while still also having traits more suited for aquatic adventures, including not only webbing on their feet, but also in a few cases, highly developed tails. In taking a page straight from their cousins, the Bicill Soridae, the members of this family were a bit more unfriendly than most present-day cetaceans, having teeth designed to pierce,

puncture and sheer flesh apart instead of filter feeding. The only good news here is that they were not as big as their co-existing relatives, being more akin to the size of bears, with the largest being about the weight of a grizzly. So, still not great. And when you take this into account, you'll also realize that not only was getting killed by a whale in the Sahara, a possibility back then, but so was getting chased by whales on land. Probably not something you had in your time-traveling bingo card. Now, the presence of whales and Sirenians on land is,

Granted, very strange. Yet it actually sets a good tone for the surface, which like the oceans was completely different back then, and this included not only the animals, but also the landscape itself, as the warmer and generally more humid climate resulted in tropical forests, open woodlands, and deciduous forests being the dominant ecosystems, allowing for both new walks of life and the continued existence of archaic groups. Additionally, thanks to both these conditions and the fact that Earth at this point had time to recover from the KT extinction event, creatures were on average larger than before too. And there was one cohort of mammals in particular that were kicking butt in the large game department,

the ungulates. Now, ungulates are nothing new, and we generally know them as hoofed animals, so think horses, giraffes, and rhinos. And although none of these three existed yet in a modern sense, the ancient Eocene ungulates could actually look a bit like their future descendants, which is nicely showcased by the brontotheres, who were also among the first mammals on land to crack the several tons mark. Superficially resembling rhinos,

these parasodactyls operated a bit like them as well, sporting horns that were not made of keratin, but straight bones, and in some specimens had various growths, suggesting that these herbivores utilized them for smacking things with their head, which would have been a very formidable attack when you realized that a few could weigh over four tons. And during their existence, Brontotheres would have been one of the most common sights on the surface, yet they were only one part of a larger trend, which I like to refer to as rhinoification.

As multiple other mammalian families were rocking similar body plans, with perhaps the next most successful example having been, the embrithopods, in order that despite still holding true to rhino's shape, were actually more related to Sirenians. They were also larger than brontotheres, with some species weighing more than 4.5 tons, which just to put that in perspective is similar to the weight of a small adult Asian elephant. And together, these two groups would have constituted a good portion of the large terrestrial animals. But ultimately, this was a three musketeer situation, as you absolutely cannot forget about the early proboscideans, i.e., the group that would one day become elephants, who

were also undergoing their very own growth spurt. And though they were undeniably big, they were not the biggest terrestrial animals just yet, with a few not even standing above your shoulder, but their time would eventually come. And given that you are watching this video, you should also be able to piece together that us primates would also one day pop off. But ironically, despite not having any 200 IQ members yet, primates were actually doing in some ways better during Isis Earth than now, as our diversity back then was off the charts, mainly due to the higher presence of forests.

And of course, more forests means more monke. And along with our own kind, other small critters reap the benefits from these forests as well, including a variety of rodents, insectivores, and modest paracidactyls, who were simply ungulates that had an odd number of toes. And overall, these long-gone days were truly integral for mammals, leading to both growth and massive amounts of diversity. And while perhaps they could be called kings of the planet, I should mention that they certainly did not go unchallenged, because even though the Cenozoic is known as the age of mammals,

it was during this time that reptiles were putting up a good fight as well, trying to hold under their crown as the rulers of earth. And given that most reptiles are, well, cold-blooded, they were also enjoying a power-up from the warmer temperatures. However, they had no interest in the rules of large herbivores, instead evolving to become highly successful carnivores, who in a few cases became the respective region's apex predators. Among them were the notorious forest rackids,

a group of flightless killer land birds who possessed robust deadly beaks and could grow to sizes that made even big bird look like small bird. And meanwhile, other birds were doing just fine as well, with both giant penguins and Titanic Flyers, both being very real possibilities to witness on any late Eocene safari. And though the birds of old were indeed threats to human-sized animals, I would probably not tell a time traveler to worry about them the most, as they had another big problem, as it was really another reptilian group that was far more scary and lethal, the Sebechidae. This was a family of crocodile morphs that had been around since the late Cretaceous.

but who had only really found their rhythm following the dinosaur's demise, which partially led to them becoming the top dogs of the Eocene, and the largest land predators back then. Now superficially, I'd probably describe them as crocodiles who looked like they were better at running than swimming. And they actually were, with each member being both terrestrial and carnivorous, while also having laterally compressed, pointed, serrated teeth, creates you tend to see more enlarged theropods, not crocs.

And these teeth alone made the sepacids, menaces, to society. But just for funzies, they also evolved the added bonus of being absolute giants. In the Western Hemisphere, you had the Brunusukas, a member whose maximum theoretical size sat at 10 meters or 33 feet long, giving it a weight of about two tons, which is greater than not only anything seen in living terrestrial predators, but also gave it a good shot at the title of the largest land carnivore ever since the dinosaurs. And then at the exact same moment that it was kicking, you also had the Dantanio Sucus to the east. who was slightly smaller at 4 meters or 13 feet, while also weighing one ton.

Yet this was still big enough to give it the title of the largest Cenozoic predator that Europe has seen so far. And the really bad news about all of this is that on top of being larger than most other animals, the sabakids were also crazily robust, leading paleontologists believe that they were quite good at killing the small handful of things that outsized them. So even in the age of mammals, things weren't always looking too great. Now, that isn't to say, though, that mammals were getting completely beat, as during this period, there were some who were making big strides in killing technology as well. Coincidentally, the situation was a bit like that of the megaherbivores, wherein lots of groups were taking a similar approach.

Except, instead of rinoification, the trend for carnivores was evolving proportionally massive heads and jaws that could dish out catastrophic damage, which is easily demonstrated by multiple groups, such as the hyaenodonts, bear dogs, mesonikidae, and the iconic hellpigs, who were on average the largest of the bunch, sometimes being the biggest mammals in a given ecosystem. And the general shift towards being a deadly bobblehead was partially the result of predators at the time favoring power over speed and ambush over pursuit, as well as just based on the fact that they were slightly more primitive overall. Albeit, there were some amalian predators who were also more derived, such as the sparasidants

and Nimravaday, the latter of which are also known as the fall saber-toothed cats, for the fact that they, well, weren't cats, but still at saber-teeth and evolved sizes and shapes that were remarkably similar to what's seen in extant felines, with the biggest of them being about the size of a lion. And in many cases, it was these mammal groups that I just mentioned who were competing with the top reptiles, that mind you, also included terrestrial snakes, representing just about the closest time where Earth's dominion was split between mammals and reptiles, at least in a certain sense. And who knows how things would have turned out if it wasn't for that pesky ice, which ultimately

threw a wrench and how things played out. As stated, the late Eocene was warmer than present, but it had been experiencing a cooling trend, one that exploded roughly 34 million years ago during the transition between the Eocene and the Oligocene, and it was all Antarctica's fault. Now, there were other factors involved, like lowering carbon dioxide levels, yet things only really switched up after Antarctica decided it did not like Australia anymore, with it drifting ever more southwards and finally breaking up with Australia, turning it into a single continent. And this was a problem as this isolation created new passages between Antarctica

and its old neighbors, which resulted in the very important circumpolar current, which simply put is a major current of freezing water that surrounds the continent, blocking not only warm water from reaching it, but also absorbing carbon dioxide. And this, ultimately led to the first permanent ice sheet that Earth had seen in a very long time, and thereby breaking the planet's iceless hot streak. But it did not stop here, as this ice sheet's formation ultimately started a feedback loop where in other regions of the world got colder as well, and ice started to grow in other places, eventually resulting in the onset of the late Sinozoic Ice Age that has gone up until today.

And this Ice Age basically rewrote history a hundred times over, as it had massive impacts on the environment and wildlife. And one of the first major changes seen was the shift of forests to open areas, such as grasslands and cool savannas, suddenly giving the edge to animals that were adapted for running and grazing. Additionally, anything that liked warmer weather, such as many, many species of reptiles, soon found themselves in major trouble as temperatures plummeted,

leading to a lot of final turnover. In fact, enough animals went extinct during this time that the Eocene-Legocene boundary is now guarded as a minor extinction event. And some of the more notable losses included are friends the Bacillosauridae, brontotheres, many early primates, and a heap load of reptiles, with even many of the surviving reptilians also suffering a massive restriction in range. On the bright side, though, it was around now that many modern lineages of mammals got their

start, with their behavior as also being influenced by the Ice Age, as colder temperatures typically led to things like thicker fur, hibernation, migration, and seasonal breeding. But this all leads to one final question. Since the ice, and thus ice age, has stuck around for the most part, will it continue to do so? And the answer is most certainly not, although the specific timeline is not crystal clear, or should I say ice clear. But barring massive natural disaster, humans are just about the only things that can tweak this timeline, as our actions certainly impact the climate. But if we assume lack of human interference, which obviously won't be the case, unless we end up on extinct zoo,

Some studies suggest that there won't be a true iceless earth for possibly tens of millions of years, almost 50 million, according to a few, with the reason being that it will take at least that long for Antarctica to shift far enough north to warm up again. So until then, Happy Feet will continue doing what he does best. Thanks for watching, and until next time, on Extinct Zoo.