ExtinctZoo - Why Water Dinosaurs Never Happened

Episode Date: November 30, 2025

A man can dream...

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When you want savings, not surprises. It matters where you stay. Hilton for the stay. dinosaurs, a topic I'll probably never get sick of talking about. And every day I find myself pondering about these terrible lizards, especially when I probably shouldn't be. And recently I was thinking about something that most dino lovers will eventually question, which is, how come there was never any fully aquatic dinosaurs?

Now if your first thought is, there was, then I can say with certainty that you are a dino nor me, because in reality, anything you think is a watered dinosaur is not. Not this, not that, nor even these. and for the most part, what people think to have been watered dinosaurs were in reality marine reptiles who were not very related. No, in the entire history of dinosaurs, we are not aware of a single fully aquatic species. And to me, that's very strange when you really break it down. I mean, here are the facts.

This group has been around for over 233 million years, had a long stint as the top dogs of the planet, lived on every single continent, Antarctica included, widely varied in size, achieved flight, and all combined, are responsible for well over 10,000 species. species, and yet none of that made it to the water full-time. Meanwhile, other groups like mammals have gone terrestrial, airborne, and fully aquatic, despite being around for a shorter amount of time and being less diverse when birds are included. So what exactly gives? Why did dinosaurs fail to overcome this so-called barrier?

And to answer that question, it might be best to actually start with how close they came or come. And looking at birds, even just the extant ones, we can see that they're not really that far off, with there being many kinds of what are called water birds. which are essentially any bird that lives on or in water for a large part of their lives. And this includes some classics such as pelicans, ducks, swans, gulls. The list goes on. And across the board, we can see that certain adaptations generally take place.

With the most common traits being, legs adapted for diving underwater, extensive webbing between the toes in order to increase surface area, and then changes in beak morphology to adapt to more watery diets. And among this group, you can break things down even further, through the sea or marine birds, who, as their name puts it, are those that have become adapted to marine environments.

And like waterbirds as a whole, they greatly vary in niche and specializations. But again, we do also see some interesting features that are widespread, such as salt glands, which are located in their beaks and help them expel excess salt, allowing them to both eat and drink really salty stuff. And some have even given up on flying in exchange for being great swimmers, like of course the penguins, who do spend half their lives in water. But again, half is not 100%. And then on the other side, there are those like the great wandering albatore.

that still fly and are really good at it, but simply live on top of water for much of their lifespans, not landing on land for sometimes years apart. Yet again, they don't do this full time, and they live on the water, not underwater. An important distinction, and so do they count as water dinosaurs? I think not. And while all the modern lineages of seabirds evolved after the KT extinction, there were also cartitious groups of them, like the Hesperorniths. So in other words, they've been a thing for a minute, and while coming close, no cigar. So with that out of the way, Let's take a look at the more interesting group, no fence birds, the non-avian dinosaurs. And while the vast majority seem to be averse to the water, there has actually been a handful

of species and families who were actually pretty good swimmers, and in some cases, possibly even semi-aquatic. Of course, the best-known group that fits the bill were the spinosaurids, a collate or family, of usually large theropods, that honestly could have passed for crocs on legs thanks to their odd adaptations. Now, each differed a bit in their own way, but some strong signs that this lot like to be in, or at least around water, included nostrils situated far back along the skull in order to avoid water seepage, cone-shaped teeth that were suspiciously well designed for catching slippery fish,

and in certain cases, unusually large and powerful tails that could have possibly assisted in swimming. And get this, at times, these tails were only loosely connected to the rest of the body, a trait not seen in other dinosaurs, but rather in fish. Furthermore, isotopic analysis and the simple fact that most bones are found in regions with abundant water, reflected this family didn't stray too far from aquatic sources. And therefore, we know Spinos were unusual, but there is still a lot of debate about just how much time they really spend in water, with some saying they only stuck along the coasts and waited,

whereas others argue that a few would have been semi-aquatic creatures. And while Spinosaurids have definitely taken the reins, as far as representing the dinosaurs in the Water Olympics, there are actually other interesting, less reported cases of water-loving dynos. Take the Houscaraptor, for example, a late Cretaceous non-avian dino from Mongolia that as far as we can tell was a dromaeosaur. Think the lost raptor, albeit even smaller, with most being the size of a mallard duck. And it possessed various anatomical features that you would not expect to find on a raptor,

namely small forelimbs that were flipper-like. And you know what flippers are good for besides dancing, swim, swim. Additionally, the skeleton also possessed a short tail that shifted its center of gravity to the front, which makes it more useful for swimming than walking, while it then also had a long neck and sensory neurons concentrated in its snout, presumably being there to help it feel for vibrations in the water, and thus leading to the idea that this was a fish eater, something that was also backed up by its teeth, which are curved backwards and highly numerous, in other words, being designed to help trap small fish caught within. In Cretaceous Mongolia, you could find even more critters similar to the

Houscaraptor, as it was actually part of a clade full of close relatives with similar adaptations, a clade aptly named the Houscaraptor-in-A, which collectively possessed at least five different genera, all from the Lake Cretaceous. And seeing that these guys were raptors, they, just like the Spinos, were theropods, as birds are too. And so this group definitely seems to adapt more towards water than other dinosaurs. But that being said, there are non-therapod cases as well. They're just a bit more rare.

And one of the more interesting examples involves an iguanodont, of all things, the Lyrtosaurus. This creature lived during the early Cretaceous, about 112 million years ago, in Niger. And his name translates to heavy lizard. And this naming can be at first a bit confusing, because despite Doltz measuring up to 9 meters or 30 feet in length, this guy was a short king, with its stomach essentially touching the ground, and yet somehow it still weighed 5.5 tons, making it suspiciously heavy, hence the name. And the implications of its weight goes beyond what it's called. For along with being heavy, it also had an unusually stocky body plan that was somewhat reminiscent

of a hippo, and therefore leading to the idea that this was a river-adapted dinosaur that spent its time near and in water for much of its life, munching out of that oh so sweet freshwater aquatic plants. Now, I will say that this hypothesis is definitely not confirmed, and the same can be said about yet another dinosaur, the leoninosaurus, an incalosaur that I dare say is even more bizarre than our guanodont, and coincidentally lived during the same era, just in China instead of Niger.

But unlike our heavy guy, this guy was a little guy, much unlike the iconic anchylosaurus, being closer in size to a dog or cat than even the average dinosaur. And opposed to the later encyclosaurus, this creature was also without a tail club knob and had basically zero osteoderms or armor plates besides in just a couple of areas, which is, let's just say, quite odd for an acylosaur, but this fact might have been due to its unlikely affinity with water. You see, when examining its remains, paleontologists noted a couple of things. One, that it had a shell-like structure that reminded them a bit of a turtle, and two, that it lacked the fusioning of its spine and hips, something which typically acts as support for an animal that is walking. emphasis on the walking part and this alone was pretty interesting to the team but what was a bit more startling was that the teeth were weirdly sharp and almost seemed carnivorous in nature oh and uh

there's also the fact there was a fish in the area where its stomach should have been signs that imply that it could have very well been semi-aquatic so evidently some strange stuff seems to be going on with the sincilosaur well at least i thought as interestingly just a few weeks after having researched this, I discover that just recently, like in the last few weeks, the new studies come forth clarifying that in reality what we thought to be Leoneosaurus was in fact just a baby and chylosaur that drowned. So, who knows? Also, RIP. Anyways, with the Leonegosaurus out of the way, you still get a fair idea of how non-avian dinosaurs did dip their toes in water. But also at the same time, never managed to fully close the gap to become fully aquatic,

similar to what we get with birds, which thus begs the question of why. And it's not that they necessarily couldn't, like there was some adamant of evolution blocking them, but rather that there was quite a bit of obstacles in the way, and one big roadblock was something totally out of their control. Competition. You see, whenever you want to get into a niche, you've got to first make sure there's enough room for you to fit. And during the Mesozoic, there really wasn't that much wiggle room when it came to the waters. When the earliest dinosaurs appeared on land during the late Triassic,

there is already the ichthyosaurs rampant in the oceans, who were not only predatorial, but could be found in just about every size. And then on top of that, you also disarupycin, the tachshunds, one of diverse diaphsid reptiles, which at that point consisted of the aquatic nothosaurs, placodonts, and more. While in fresh water, carnivorous amphibians, fish, and phytosaurs were just a few of the problems that potential water dinosaurs would have had to deal with. And so, with that many adversaries, it didn't really make much sense for dynos to try and take over the water, Rather, it just made more sense to double down on land.

And this barrier of entry, so to speak, only intensified as the Mesasoa had progressed, with animals beneath the waves evolving, diversifying, and, simply put, becoming more terrifying, with pleasiosaurus, giant fish, and large crocs, all becoming stark realities, realities that in some cases were even bigger and badder than their predators that dinosaurs cooked up, which is a saying a lot. So, not a whole lot of motivation for them to get their feet wet. I don't blame them, but it wasn't only other animals that kept them from taking a dive. It also involved them, as well. As it was the design of dinosaurs that was another major hurdle in

going fully aquatic. And one of the main issues seems to have to do with the reproduction. Now, all dinosaurs are archosaurs, which is a clade that contains things like birds, non-avian dinosaurs, of course, crocs, terrors, yada yada. And what one will notice when scouring these archosaurs is that the vast majority of them, if not every single one of them, are something called oviparous, essentially meaning that they lay eggs outside of the body. And when you realize that the vast majority of fish are viparous too, in fact 97% of them, you'll probably think that dinosaurs would thus make the perfect candidates for water. Yet a key difference seen in fish in archosaurs is that fish of soft gel-like eggs,

whereas archosaurs are rigid, hard, and in the case of dinosaurs, made of calcium carbonate. Three things you actually really don't want if you're trying to lay eggs in the sea. as the texture or material ultimately was designed for gas exchange and exposed air, not underwater. And what would happen is that the pores in the shell would become waterlogged if you place them underwater, meaning that the embryos would suffocate or drown if the water penetrates enough. Because I'm not sure if you knew this, even though it's probably not that surprising, but eggs still have to breathe. And even in high humidity, chicken embryos have been known to drown.

So, full-on water is probably not a great idea. And then on top of that, their rigid shapes make it even harder for them to adapt once submerged, essentially causing a structural issue. In combined, these design flaws are pretty dang hard to just evolve away, especially because they're so useful on land. But there is obviously a way around to this, which is that other animals have gotten past this by becoming vivorous, i.e. doing live births.

Take snakes, for example. Most lay eggs on land, being of itperous, like dinosaurs, but 30% of them perform live births, including those that you guessed it are fully aquatic, aka sea snakes. with there being only one exception to this rule, the sea crate, who still in fact does lay its eggs on land. So that's pretty much the solution there. If dinosaurs wanted to become fully aquatic, they would likely have to drop the hard eggs on land and develop viviparity.

Yet strangely, this seems to be much more challenging for them than for other animals, snakes obviously included, who are Lepidosaurs. And Lepidosaurs is a superorder that also contains lizards, a superorder which, by the way, has evolved live births at least 115 times. While on the flip side, can you guess that number for archosaurs? Zero. Maybe one to two, and still absolutely nothing compared to the Lepidosaurs. And this comes back again to their hard-calcified closed shells, as Lepidosaurs, while also having shells in the oviparous species, typically lay soft and leathery shells instead.

Which apparently makes a big difference when it comes to making the leap to doing light births. And even if we magically made it, so a dinosaur did not have to lay eggs on land, there is still another trait about them that makes everything harder, their bones. Get it? Now, this does not apply to every single dinosaur, but many of them possessed pneumatic bones. And no, that is not a health condition. Well, except if you're a human and that's found in which case, I'd definitely say that is a health condition, but in dinosaurs it just means that like birds, certain non-avian

dinosaurs had more hollow bones, with air spaces being littered throughout them. And this helped dinosaurs do a number of things, including reducing their overall weight, achieve a certain skeletal mass distribution to help aid with balance, especially in the heads and necks, And then finally, help with higher altitudes. And this is great to know all, but it turns out that hollow bones aren't exactly the best if you want to swim for long times, as the amount of error they retain caused dinosaurs with them to basically be like living boys, making it incredibly difficult for them to dive and stay submerged.

And in order to get around this, the bones would have to become more dense over time, which is possible, as we do see it in some spot of swords, but it certainly takes a lot of rework, and it would require quite a large gap in a niche to the extent that it would cause evolution to turn away from the benefits of pneumatization. On top of this, the air sacks inside of the pneumatized bones, which caused all that air, allow them to have a very efficient way of breathing, but at the same time raises risks of compression when submerged. In other words, more air sacs equals higher chance of things going wrong when diving.

And even in penguins today, we see that just to go low, they have to do some pretty major breathing exercises beforehand in order to empty the gases within their air sacs, and thus reduce buoyancy. And even still, it's not perfect. So that's just another layer to it. They would have to pretty much restructure their entire breathing system. Well, at least those with pneumatized bones. And that is a piece of the pie too, in this sense that on top of the specific barriers,

there are also more general barriers that prohibited dinosaurs from evolving into fully aquatic creatures. In other words, going aquatic is simply not an easy task for anyone to do. Being pretty much hard enough to make a no-hit run in the Souls franchise game seem like a walk in the park. And part of this is the fact that animals, which do make the transition, to not only arrange their body, but also their senses, with eyesight, hearing, and smell, all needing to be heavily revamped to operate effectively in water. I mean, have you tried opening your eyes underwater? Doesn't work great.

Not to mention, you also have the dilemma of locomotion that you need to solve. And this might seem easy, as in whales, hands turn to flippers, and they evolved the tail. But it's actually not that simple and non-avian dinosaurs, even though many of them often do have powerful tails. Now, this is not a universal thing, but multiple groups during the Mesozoic took a very much on certain trends that made it very unlikely that they'd be able to evolve features for aquatic locomotion. For example, in theropods, many groups were evolving smaller arms as skull size and jaws became more important, whereas in some other theropods, it was a focus on gliding

and flight leading to wings instead of, well, flippers, even though we have seen that wings can go back to flippers, just a bit harder. And regarding ornithicians and saropods, it is not universal again, but we do see that many of them developed robust shorter limbs that were designed to be weight-bearing, pushing them even farther from the aquatic finish line. And really, besides the tails, there really wasn't a universal feature in dinosaurs that would have made it easy for an aquatic transition in locomotion. And so, the list of problems preventing the possibility of a water dinosaur is already getting quite big, but sadly, it's not at the end yet for our favorite group, as an additional issue relates to something quite distinct for dinosaurs, and that is size.

Now, as you know, non-avian dinosaurs were pretty huge, and this isn't a case of me focusing on the big famous ones, but rather, across the board, they were pretty darn hefty, with the average dinosaur being about 3.85 tons, so more than the weight of nearly every car you can drive on a public road. Now, obviously, these average sizes did them a lot of good, allowing them to essentially become untouchable to other groups. But it did help them keep them stuck to ruling land, as larger animals tend to have higher conversion costs as opposed to smaller or medium-sized creatures.

And what I mean by this is that based on fossil evidence, most animals which transitioned to the waters full-time, descended from animals that weren't that huge. And before you say, well, look at whales. Well, I'd say back to you, look at the first land-dwelling ancestors of the whales, as well as also the Sirenians, Mosasaurus, and Saraturigians. They were all we lads compared to their descendants. And taking this all into account, we arrive at the conclusion that while technically, Not being impossible, dinosaurs did have their work cut out for them, just as birds still do.

And honestly, it's not for a lack of opportunity, as there was a great one right after the KT extinction, seeing that many of the big bads in the water were eradicated and thus opening up the niche. But, unfortunately, along with the big bads in the water being eradicated, so were many dinosaurs on land. Well, in fact, most of them, with the only long-term survivors being, of course, the avian dinosaurs, who were more interested at the time in flying, or only swimming parts, but, you know, hard time. And to be honest, they likely wouldn't have fared that well anyways compared to the

mammals who also survived, obviously, as they had already evolved above a parody, making the transition a bit easier for them, or rather for us. And we do see that by 10 million years after the asteroid, we mammals had already made the leap. So tough luck to the dinosaurs. Although, who knows, maybe one day birds will get in the pool and never look back. And that idea does lead to the interesting speculative question of what exactly what a dinosaur have to have been like. And of course, This is seriously theoretical and impossible to answer completely correctly, but I do think an educated guess can be made by examining what were the most marine-adapted archosaurs of all time, and by a clear margin at that, the Thaladosukians,

and more specifically, a sub-family of them, which was dubbed the Metro Rancordia. And if you know, you know. Remember how he said that maybe one or two archosaurs developed live births? Well, this family is one of those numbers, and of all the archosaurs, they were the most adjusted to pelagic lives, possibly having achieved fully aquatic status themselves, whilst their ancestors superficially resembled crocodiles. So that begs the question of what changes did they undergo? Well, they lost their scales, replacing them with smooth, hydrodynamic skin,

and their hands and feet transformed into large paddle-like flippers, which numbered four, unlike what happened in Cyrenians and cetaceans, which have two flippers in front, and then just one large tail. But speaking of tails, these marine crocs worked on that too, developing tail flukes that were vertical in shape. And all in all, they kind of looked a bit like mosasaurus. So if we had non-avian dinosaurs make the leap to water, or should I say, dive to water, perhaps they would too. And frankly, envisioning a spinosaur or tyrannosaur as a mosasaur wouldn't be all that difficult, strangely, and also certainly not comforting. And in the case of herbivorous dinosaurs, maybe they would have evolved the ability to feed on seagrasses.

And perhaps found their already defensive adaptations shift be water-friendly, turning into strange. structures similar to what's seen in swordfish, sawfish, etc. With the one general rule being that likely whatever happened would make sure to take hydrodynamics into account. So in other words, I'm not sure if multiple horns or thagomizers are staying. But that being said, who knows? Because maybe dinosaurs could have also taken some more untraditional approaches to going fully aquatic, like some groups have in the past, such as the Desmostylians, which in spite of being fully aquatic, actually retained their limbs instead of developing flippers or tail, deciding to forego speed,

and instead prioritizing size to be their main deterrence. And since dinosaurs have already very much nailed that part, maybe they would have evolved the same way, living slower, chiller lives, which might have consisted of walking along the sea floor. Or who knows, perhaps these out-of-date constructions showing dinosaurs and swampy swamps, were really what could have been. And then in the case of birds, I suppose it's too early to say, but just to reiterate, whatever does happen, they've got some ways to go.

And frankly, if the future does hold fully aquatic birds, it might not be a great thing. thing as it probably implies that the earth experienced quite the serious shakeup, something that I'd personally rather avoid. Thanks for watching and until next time on Exteam Sue. Ambition comes in all shapes

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