ExtinctZoo - The Only Marine Mammals That No Longer Exist

Episode Date: November 8, 2025

Marine mammals are all around us, whales, seals, manatees, the list goes on and these lot have been a staple of the earth for tens of millions of years. However, it turns out that there used to actually be even more of these guys, as there is one (and only one) marine mammal order that no longer lives, and you probably have never even heard of it.

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When you want savings, not surprises. It matters where you stay. Hilton, for the stay. Roughly 225 million years ago, across the plains of late Triassic Pangaea, a brand new kind of animal was on the prowl. To the naked eye, it might have come across as small and underwhelming, especially compared to the early dinosaurs and archosaurs it lived alongside. But unbeknownst to them, and even to itself, its presence was huge news, as one day it and its ascendant would completely change the world.

And who was this? Well, none other than our own, a mammal. And from then to now, mammals have made their way to the top. being in some ways akin to what dinosaurs were in the Mesozoic, in other words, rulers, with now nearly unparalleled diversity, and thus far over 6,000 species of mammals are known of, and that's just living. And this includes mammals that have evolved to take flight, live underground, live on ground, and then of course inhabit the waters of Earth for full-time or near full-time, aka the aquatic mammals. Typically, biologists consider there to be 27 extant orders of mammals, with three of them

being either partly or entirely made up of marine mammals. And the best known of this trifecta is arguably the cedar ardeadacty, which includes animals like whales, dolphins, and porpoises. Next, we have the sirenians, or sea cows, that are represented by manatees and dugongs. And finally, there is the carnivir order, which is home to many mammals, both terrestrial and aquatic, and in the marine department it includes pinnipids or seals, marine musselids, and then even one bear, the polar bear, who is home to be. is, surprisingly, or perhaps unsurprisingly, counted as a marine mammal due to its dependency

on the ocean and sea for survival. And together, these marine orders stretch across every continent, greatly ranging in size, have vastly different food preferences and sometimes very ancient roots, with both cyrenians and cetaceans getting there start around 55 million years ago. So, these groups have long been a part of Earth's history, and are a testament to the success of marine mammals. And just to drive the success home, another fact that proves this is that the vast majority of marine mammalian orders, which have evolved, are still here today. And actually, there is only one order of marine mammals to have arisen that is no longer with us today, and therefore representing the sole group of marine mammals to have ever gone extinct.

And there's a good chance that you've never even heard of them. So without further ado, this is the Desmostalia, which means bundle pillar, but we'll get to that later. Strangely enough, despite being the only group that didn't make it, the Desmostalians were actually the most recent Marine Order to evolve. But with that still happening, a long, long time ago, with their origins dating back to the early a legacy period, around 33.8 million years back, give or take. Back then, the Earth was very much unlike the one we know of today.

Sea levels were yo-yoing across the world. Eurasia had an inland mega-sea. South America was being run by giant flightless dinosaurs. The largest land mammal ever was walking around. And maps in general would have seemed a bit off. So wacky, to say the least. But this is what apparently was required in order for us to get the same. the Desmostylia, who of course matched the vibes by being quite strange themselves.

And as far as we can tell, the first genera of this bunch to evolve was the behemotops, who popped up along the northern Pacific, specifically along the coast of the U.S. and Canada. On top of being the first, the behemotops was also, unsurprisingly, the most primitive desmosylian discovered thus far. And just taking one look at it, I'm sure you've gathered it was quite an unusual creature in general, too, resembling some sort of hippopotamus that didn't quite get the memo on how to be a hippo. Furthermore, along with its superficial looks, its bones suggested that behemotops was eerily hippo-sized two, with the adults having measured some 10.6 feet or 3.2 meters long, and weighing

2.2 tons. And so, with these two things in mind, it's no huge surprise that when bones belonging to this order were found, many thought they had stumbled upon a primitive ancient hippo, not a new order. There was one problem with this, though, that confuse everyone, which is that hippos, or rather hippopotamids, only appeared in the fossil record about 15 million years ago. So, in other words, quite a large gap. And lo and behold, it's turned out that behemotops and its kin aren't some sort of missing link, but rather uniquely their own group, who ironically aren't even that closely related to hippos. Go figure.

And actually, we don't really know what they're most related to, but the two most common ideas being that they're most close to Sirenians and elephants, or that they are more related to the parasidactyl. aka the autodongulets, which encompass animals such as horses and rhinos. In both of these hypotheses stem from the shared similarities that Esmostylians share with these animals, with its jaws and dental structures being more like that to manatees slash elephants, while its limbs hold more similarities to paracetactyls, especially basal ones. Now, their enigmatic nature does not stop at simply their classification,

as these guys in general were quite mysterious, with even their general body shape being very intriguing, with every member to have evolved being quadrupeds, with robust, massive limbs, and large bodies, which is nicely highlighted by the fact that the smallest species, the Ashura Latakasta, was still pretty big, measuring about 5'5 foot 6 inches in length, and would have weighed hundreds of pounds or kilos. Beyond body plan, paleontologists have also noted other universal traits, specifically among their skulls, with the rostrums having been broad and elongated.

And then on top of this, they typically also possessed forward-facing incisors and canine tusks. So again, not too hard to see why they were first confused for hippos. And based on this general description, you definitely would think that if you traveled back to the Eocene, as you would see these guys living along the shorelines and coasts, acting a bit like a, well, hippo. But instead of a lake or river, these guys preferred the whole dang ocean. But here's the kicker, no pun intended. As despite their hippo-e looks and clearly defined four legs, these guys probably didn't spend any time on land. Like, Nata, as DeSmosylians, as it turns out, were fully aquatic.

marine animals, meaning if you time travel to this period, you wouldn't see them walking along the beach, but rather while you were out scuba diving or snorkeling. Although, disclaimer, I would not recommend doing these activities during this time period. Now, originally, it was believed that Esmostylians were not fully aquatic, and no shame to those scientists because I'd have thought the same, with their earlier studies on this group, finding them to be instead semi-aquatic, or possibly even more terrestrial than they were aquatic, given their well-developed limbs. And while they were swimming, it was originally suggested that members of this order would have needed to rely heavily on their powerful forelimbs just to move. But over the years, as more species have been found, along with better preserved specimens, traits started to be identified that showed pretty clearly that despite the odds, these guys did not need land.

And the biggest sign of this was that, although their limbs were large and powerful, they were not built in a way that could support their hefty white bodies on land. And to kind of picture this, think about the people from, Wally. Additionally, every fossil belonging to one of them thus far has strictly come from Marine strata, while the bones themselves are also highly spongy, which in fact are a lot like those for cetacean, which would have aided them in buoyancy, cut down on weight, and helped to store energy-dense fat, which are all essential ingredients for a watery lifestyle. And this isn't the end of the list, as Desmostalians had retracted in airs as well, in other words, nostrils, plus raised orbits, both characteristics designed to keep water out of places you don't want it. And guess what?

But, these adaptations are usually only seen in other aquatic mammals. And then just as the final nail on the coffin, latest isotopic analysis shows that their diets reflected purely aquatic environments, not terrestrial. So there you have it. These guys are swimmers, not walkers. Yet I do admit that there are still some who push the semi-aquatic narrative, but to that I say, slander. But to be totally honest, they actually did walk. just a, not on land, rather along the sea floor, where they would have done most of their feasting. And yes, they did have those pretty gnarly incisors and canines,

but they weren't on the bottom looking for unfortunate prey, as they aren't thought to have been carnivores, but rather big old herbivores, with a feeding strategy so unique, it's only ever been seen in Des Mo Stylians. See, I wasn't joking when I said these guys are seriously odd. Now, you've all heard of chewing, right? Don't answer that, rhetorical question. But obviously yes. However, for the decimostalians, it would have been an alien concept, as despite having teeth,

these guys didn't really munch, well, in the typical fashion. Rather, they simply clenched their jaws and teeth, meaning they didn't move their mouth side to side, like we do, rather purely vertical, kind of like a stapler coming straight down onto something. And that's it. And they would do so in order to fully uproot their food of choice, aquatic plants, such as kelp and seagrass, with the northern demostylians in particular, especially liking to have sweet sweet, sweet kelp. And this bizarre way of clenching their teeth stems from their strange shapes, namely the molars which were constructed like columns or pillars, bearing resemblance somewhat

that multiple pipes stuck together or a bunch of clustered volcanoes, hence their name, meaning bundled pillar. And going full on stapler mode instead of chewing is just the beginning to their eating process. Because once they uprooted their food, instead of grinding it down like normal animals, Desmostalians instead bust out their necks, or rather throats, which had extremely powerful muscles that could suck like a vacuum from hell, allowing them to siphon grasses down at mind-boggling speeds. Perhaps don't put your hand near these guys. When you combine this odd way of feeding with their overall abnormal builds, the Desmostalians

come off as some sort of wacky experiment. But nevertheless, it seemed to do the trick and worked pretty well for them. Is over the next 20 million years or so, the Desmostalians would slowly spread out throughout large parts of the Pacific, and eventually even evolving into two distinct groups. one being the Desmostylidae and the other the Paleo Paradoxidae, or as I like to call them waterboys and superwater boys, as though there are multiple differences between them. A big one is that members of Desmostylidae like Desmos stylus or Cornwallius or Behemotops were mainly found in shallower waters that did not exceed 30 meters or 120 feet.

Additionally, this subfamily is also known to have traveled into more exotic environments, including freshwater channels and brackish estuaries, whereas the Paleo-Pyroarer, Paradoxidae, which contained the Osora and Paleo Paradoxia, lived in much, much deeper waters, and were exclusively found far offshore. Talk about pioneers. And they didn't just achieve an impressive range when it came to water depths, but also dimensions. As like I mentioned, this order also got sizey. From the get-go, they already tended to be on the heavier size, and that only increased

as they evolved further, with most reaching over a ton, while the biggest estmostalia were comparable to the largest Iranian species to have ever lived, the stellar sea cow. which might as well have been called the Stellar Sea's elephant, because it was a unit. And based off of it, the largest Decemostalions were possibly over 10 tons in weight. So move over Modo. Now this being said, the Decimostalians were not as long as the Cyrenians, given that all of them lacked long tails, that once upon a time was actually a common belief. But in reality, they had remarkably short tales,

indicating that they lived rather chill and slower lives, where speed was not the name of the game. But with that said, paleontologists have noted that across the genera, bone density widely varied, with some members having more dense, heavier bones, and others lighter and more porous, suggesting that if you swam alongside them, you would find that certain ones were utter slow-pokes, while others were a bit more lively, relatively speaking, as in general these guys were not what I consider speedsters. And a bit like manatees of today, Des Mo stallions probably heavily relied on their size to get ahead in life, lacking any clear adaptations for offense or defense.

Now, yes, they did have a robust build in general that aided endurability, as well as their incisors and tusks, but unlike those seen in hippos, which can have sword-length ones, these were not weapons of mass destruction, and beyond some maybe friendly competition between Desmostalians, it seems like a stretch that these teeth would have been used to fend off the true beasties that lurked below, which during their time consisted of marine crocodiles, predatorial toothed whales, and giant sharks, including the Megalodon and its closest kin. So obviously, that's a lot to deal with, but like the current manatees, Desmostalians managed to prevail.

And not just that, but their diversity reached surprising levels. And so far, we know that at least eight different genera lived between the oligocene and myocene. And I guess this also proves that being weird isn't a bad thing. And we even see that Desmostalians tended to get weirder and more specialized over time, which is best highlighted by one of the last species to have ever lived, the Neo-Paradoxia. This member hailed from the Montre formations in North America, and it was completely unlike its relatives. For one, it had a paracidol process that was massive, lengthened, and extended laterally, whilst its temporal and mandibular fossa were both proportionally larger

and deeper than what was seen in other Desmostalians. Now, don't get it twisted, these adaptations do not imply that they started to become a bit meaner and more dangerous, rather just that neoparodoxia had become more nuanced and picky when it came to eating, which is pretty absurd when you realize that even the least specialized these lot still had a feeding strat which was unseen in anything else. And though their high degree of specialization helped them at certain stages, it would also be the key behind their eventual downfall, highlighting the flaw in this group. And you're probably thinking about to mention something about the climate, yet unlike many other extinct animals, it wasn't the changing of temperature or sea levels that exposed the

Desmostalian's weakness. Rather, it was none other than a fellow marine mammal, the Sirenians. You see those innocent, adorable-looking faces? Well, turns out that they might have blood on their hands, or flippers, because there is some rather interesting beef between them and our protagonists. You see, Sireenians were the older of the two. First, appearing about 55.8 million years ago. However, they didn't actually get a huge head start off of this, considering that Sirenians didn't make the jump to fully aquatic until the end of the Eocene. And so this pretty much means that Sirenians and Desmostalians hit the waters for good around the same time, kickstarting somewhat of a rivalry between the two, with them both eating

a lot of the same foods, mainly kelp and seagrasses. But instead of the old clench and suck methodology, the Sireenians evolved a more simple approach, utilizing strong prehensile lips to strip the vegetation before using the oh-so novel, drum roll please, chewing to munch the matter up. Doesn't seem like a big difference, but it was, and a really important part of this is that by using their lips and the strategy, they would leave some of the plant's base behind, whereas the desmosalians would totally suck up every single last bit of plant,

leaving literally nothing behind. A critical error, one that we humans know quite too well, as in doing so, it left no chance for the plants to regrow. While for the Sirenians, on the other hand, they could eat, leave some behind, and eventually return to find that magically new snacks had appeared. Amazing, and quite the competitive edge over time. And this wasn't the only thing that the Sirenians had over the Desmostylians, as instead of keeping their limbs and getting a small tail,

Sireenians turned their hands into flippers and their back legs into one powerful tail. And this allowed them to absolutely steamroll the Desmostalians. And we actually see that the moment Sirenian diversity started to rise, Desmostalians started to fall, and they get rare and rare, and rare within the fossil record. For a long while, the two orders were able to coexist, but eventually one had to go, and it sure wasn't the Sirenians, and by the late Miocene, the Desmosalians were on their last legs, literally, as only the Desmosylos and Neoporodoxia remained, with them both being

restricted to the Northern Pacific, and soon enough their time ran out as well, perhaps facing competition from the Ducey Sirens, who had recently doubted to colder climates and thus moving farther north. And with these two guys vanishing, so did the Desmosyllians as a whole, ending a rather short existence for an order. So next time you see a dugong or manatee, yes, admire their cuteness, but also take note of their history-altering past, which perhaps robbed us of a pretty funky group. Thanks for watching, and until next time on. Ambition comes in all shapes and sizes. At First Citizens Bank, we roll with your goals, because we're built for what you're building.

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