ExtinctZoo - When Dinosaurs Almost Made A Comeback

Episode Date: May 9, 2026

If you ask the average person when the dinosaurs rule ended, they would say 66 million years ago when that big ol mean asteroid struck. But in truth, this may not really be all that right...seeing that not so long after their demise a new group of dinosaurs emerged, that caused their own share of terror (pun intended).

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Of all the groups of animals who've ever lived, I'd say there's a fair argument that dinosaurs have been one of, if not the, mightiest to exist. And in their heyday, they established a rule that would go unchallenged for over 140 million years, leading to an entire era, the Mesozoic, being nicknamed the Age of Dinosaurs. During this time, no other group of animals was able to come even close to challenging their dominion on land. And it was only after the referee stepped in 66 million years ago, in the form of a giant asteroid, that things finally changed. Now, the asteroid's impact was catastrophic for all life, killing 75% or more of all species.

But dinosaurs were especially affected, thanks to their large sizes, and within a short amount of time, all non-avian dinosaurs had vanished from the face of the planet. But this wasn't really the end for the terrible lizards, as one group managed to slip by into the Centezoic and are still all around us. The avian dinosaurs, aka birds. This group of familiar animals are indeed 100% dinosaurs, and specifically belong to the theropod clade, the same to which the T-Rex once belonged to. And today they are found throughout the world and are represented by over 10,000 living

species, which is no doubt very impressive. Albeit with that said, no living species of bird possesses the same imposing presence that the non-avian dinosaurs once possessed. However, what some may not know is that not long after the demise of the non-avian dinosaurs, there was actually a family of carnivorous theropods that sprung up, which ended up coming alarmingly close to being just as terrifying as their predecessors, and who were the dinosaur's strongest comeback attempt to date. And this menacing group of avian dinosaurs primarily resided within South America, and it would

go on to create a powerful dynasty to last for tens of millions of years. And these were the Forest Rackeds. And maybe this name doesn't mean anything to, but their nickname might, as over the years they have more often been referred to as the terabirds, as along with being flightless, avian dinosaurs, they were, well, quite terrifying. And each and every member seems to have come equipped with the same starter kit, and that is a relatively giant hooked beak, a tall vertical stance, powerful necks, and razor-sharp talons on the end of their feet. It also helped their case that not one, but multiple species from this family managed to reach absolutely massive sizes

for a carnivorous bird, with a few of them even becoming some of the largest centazoic predators who have ever graced South America, as well as taking the top spots when it comes the predatory birds. Yet, while everyone likes to focus on the glory days, so to speak, the Tarabirds had humble beginnings and did not start off as giants. Their fossil record is incomplete, but it's believed that they descended from a group of birds capable of flight who survived the KT extinction event and ultimately became flightless in order to fill a new niche, with the first potential terabird, the Paleo-Sylopterus popping up as far back as 53 million years ago during the early Eocene, when the Earth was still very hot and Brazil was enduring

heavy rainfall. And this primitive terabird is not only, possibly the oldest of its kind, but also one of the smallest and slenderest of the terabirds, with adult specimens only reaching to about one meter or three feet in height, making it about the same size as a stork. But equipped with long, agile legs, this smaller size did allow the Paleosylopterus to be very quick and fast, which aided in chasing down prey within the dense forest of Brazil. However, this little guy was not the ecosystem's apex predator just yet, as that title went to the far larger animals in the area, which at the time included a variety of both crocodilians

and snakes. And unfortunately for the terabirds, they would need a way to a while longer for their shot at the top, because the second terabird to appear didn't have it easy either. And actually, this second bird might have been the first depending on who you ask. As in recent times, new studies have raised questions on the true nature of the Paleosylopterus, and if it really was a terabird or something of its own. If it really was something of its own, in other words, not a terrabird, it would add a whole new layer mystery to this group, as the next oldest species is actually still unidentified. To be exact, a tibiotarcyst dated to the middle Eocene, some 43 million years ago in Argentina, has been of late, frequently cited as the oldest conclusively proven terabird, as the bone is an exact match, as far as defining characteristics go, compared with later more complete terabirds.

Yet, because it is fragmented, no name has been given to it, only that, just like the Paleosylopterus, this guy was more bird than terror, with an estimated body mass of just five kilos or 11 pounds. So, something most people can curl with one arm many, many times over. So yeah, definitely not an apex predator either. And actually, it seems like in the beginning it was actually the terror birds who were the ones being terrorized. As numerous tooth marks in the bone suggest that this little guy was the victim of a vicious attack by a small to medium-sized predator. And possibly the Neolestes, a hypercarnivorous marsupial that lived alongside it. and seems to have been a bit farther up the totem pole.

But that said, the mammals would need to savor this win, as their reign in South America was on a timer, as over the coming millions of years, the tarabirds would start to slowly power up. And it's actually thought that other birds might have had something to do with this, as there were other carnivorous birds in the area too, which along with the expansion of grasslands, led to a fiery arms race that ramped up fast.

And such that by the time the Eocene was coming to a close and the legacy in it started, the terabirds had already begun to reach giant sizes, such as demonstrated by the fysornis, which was also found in Argentina. Sadly, exact measurements of this terrab bird are not known as far as height goes, due to the limited remains. But going off what we do have, it's been estimated that the fysornis would have at the very least stood taller than the vast majority of humans, while also being quite hefty, weighing up to 240 kilos or 530 pounds, and already making it heavier than the largest living bird of today, the ostrich,

and actually more comparable to a grizzly bear than any modern bird. And this large weight was not only due to its height, but also due to its bone construction, which was remarkably robust for a terabird and rendered it among the largest terrestrial predator within its environment, if not the largest, of a legacy in Argentina, and resulting the fysornis being among the earliest terabirds to be an apex predator, outsizing both the known snakes and terrestrial crocs in its ecosystem. And with this size increase, we also see the emergence of the terabird's massive and powerful hook beaks that were longer than rulers and were sharp enough that you might as well consider them

to be two blades, just stuck on top of each other. And in fact, they were so sharp and robust that some have referred to their be beaks as bolt cutters. So yeah, you do not want to be bitten by this thing. And armed with this absurdity, it's been speculated that large terabirds would have killed prey by basically bringing down their beaks like murderous axes, essentially cleaving through flesh and dealing catastrophic damage with repeated strikes. Other studies have also proposed that terabirds might have had a surprising powerful bite as well, which is contrary to earlier beliefs, and a potent ability to kick with their long robust legs, which, as a reminder, armed with razor-sharp talents, and giving them more than a few options to dispatch prey. So whatever you were, you definitely want

to steer clear of these large terabirds. And this whatever part would have also included other terabirds, as besides the fysornis, there were actually smaller to medium-sized tererbirds around as well, including the under soreness, for example, who would not have been tall enough to peer over your head. Though with that said, over time, the trend for terror birds would become clear, and that was that these guys were only getting larger, not smaller, and becoming much more specialized in the inflicting terror part, which we can see in the late legacy in terabird, the parrifice soreness, which wasn't only a giant as well, but also had evolved an extremely hooked tip on their beak, even for a tererbird, and thus suggesting that

it was uncomfortably good at tearing, ripping, and slicing flesh. And somehow, even it, and those that came before, would not be the figurative mountaintop for the terabirds. as that would arguably only come in the preceding Miocene Epoch, when the Terabirds once again reached new limits in size, and the continent saw the emergence of the family's largest members, as well as the most iconic, the Kalenken and Brantornis. Surprise, surprise, both of these units hailed from Argentina, and likely actually coexisted with each other in life, each holding their own different records amongst the Teribirds. And for the Kalenkin, this was height, as adults can measure three meters or 9.8 feet tall at the head, which is, by the way, taller than any known horse, while also weighing a maximum,

possibly 300 kilograms or 661 pounds, making it about the same weight as a male grizzly bear. The bronze tornus, on the other hand, was not as tall, with adults only being about 2.8 meters or 9.2 feet tall, yeah, only. However, it had a stockier and more robust build, which made it likely heavier, with individuals weighing anywhere from 770 pounds to 880 pounds, or 350 to 400 kilograms, making it not only the heaviest terror bird, but also the heaviest carnivorous bird of all time, and the fourth heaviest bird to have ever existed, period. There is one problem, though, which is that the broad hornus may not have been a terror bird at all, or even a carnivore, which would certainly hurt the terror part.

You see, in recent years, certain paleontologists have questioned these old assumptions about it, referencing the lack of its remains, as well as its toe claws, which bears some resemblance to those found in herbivorous birds. And through differing studies, it's been claimed to have instead been a gastronithiform, a charyamiform, or even its own thing. Now with that said, there have also been other studies that push back on this and maintain its terabird classification, citing certain features that the brontorness possessed, which are seen pretty much exclusively in terrobirds, such as the shape of its thoracic vertebrae. So to be honest, until we have more complete remains, who really knows what this mystery bird was.

However, if it was a tererbird, what is definitely true is that it was still quite unlike the other kind. due to its immense weight and its contrasting build, which was opposed to the more nimble skeletons such as what was seen in the Kellynchon. And so if it was a terrabird, it likely more heavily relied on ambushes to capture its prey, as it certainly had slower locomotion to accommodate its enormous body mass. Now in the flip side, the Kellynkin and other more nimble birds seemed to have been unsurprisingly extremely fast runners. And we can especially see this by going off their legs, which much like ostriches had short

thigh bones but elongated bones in the lower leg and foot, allowing them to chase down prey fast-paced pursuits. And when I say fast, I mean fast, as paleontologists even believed that these terrobirds, despite being giant, could have exceeded 30 miles or 48 kilometers per hour at top speed, making them faster than the fastest recorded human ever, Usain Bolt. And this speed allowed the terabird to chase down pretty much every animal in their environment, despite again, being huge. And it wasn't just in Argentina that we see giants at the Kellanquin or Brontorne emerge, as during the exact same time in Colombia, there was yet another giant terabird that was supersized living there and possibly was even bigger than its Argentinian counterparts.

Specifically, in late 2024, a report came out that a middle leg bone belonging to an unidentified terabird found some 20 years ago had possibly been attached in life to the largest terabird ever. Now, the singular bone is all we have, so it's by no means confirmed. But based on its dimensions, it seems that this new species was at the very least bigger than 150 kilos or 330 pounds and taller than 2.5 meters or 8.2 feet. The only problem is, we're just not sure how much taller or how much bigger, with the most liberal estimates saying that it could have been between 5 and 20% larger than anything seen previously in the family, which, if true, would also mean that terror birds made to the podium for the top three largest birds of all time. So, watch out, Big Bird. What's super interesting, though, and also quite scary, is that this leg bone keeps in line with the rule that water is always more nightmarish than land, as this fossil had signs of predation, with the suspect in question,

actually coming from the largest Cayman of all time, and possibly the largest crocodilian, period. So, as you can see, following the asteroid, reptiles were doing just fine. And like many animals today, it's not that this terror bird wandered too close to the water's edge, and thus ended up beginning hit with the Unor-Rverse card, with the terror being flipped right back at them. However, even with this in mind, at the end of the day, this mystery bird is still considered to have been an apex predator, and the fact that it had no often-reoccurring natural predators. And surely the vast majority of animals around, it, at least on land, feared it, rather than it fearing them. And I point this out because for a long time, it was actually thought that large

terrobirds were a bit like chihuahuas, in that they were all bark and no bite, being instead small prey specialists, hunting primitive rodents, reptiles, and smaller mammals instead of megafauna, given how their schools perceived as weak at the time. But the latest research shows that tererbirds are probably just fine at tackling small game and large game alike, with there being absolutely no problems. And this new more supported idea stems from the discovery that in fact two types of skulls exist within the family members, generally speaking. One being the xylopterine skull type and the other the Teribird skull type, the latter of which is only seen among the bigger members, and is mainly characterized by being more rigid.

And it's this rigidity that allows it to have much higher bite forces, higher stress tolerance, as well as giving it a bit more pecking power, and thus leading to the belief that these giant nightmares were capable of taking down prey larger than themselves. And along with their more nightmarish physical traits, the terrabirds also evolved another advantage that assisted in their long reign. And that would be their senses. Their eyesight and hearing in particular were quite potent as shown by studies in their brain cases and skulls. And regarding their eyesight, it is believed that, while they did not have a sharp vision

as eagles or hawks, they still had by all means excellent vision and possessed the crucial ability of being able to clearly see prey in both extremely bright areas and dark areas, allowing for a high level of adaptability. for hearing, their inner ears were developed in such a way, which suggests that terrabirds were especially good at detecting low frequencies, which they then could have used to track and locate prey. Additionally, their hearing was in fact so sensitive that they could actually hear footsteps of small animals that were completely hidden by undergrowth, and that is this fine-tuned and sense of theirs, which is currently believed to have been one of the main ways terabirds found

prey. And so, hearing, eyesight, and all the other physical traits combined, allow the terroberts become dominant predators for millions of years. It wasn't just Argentina or Colombia that they would end up dominating, as Brazil and Uruguay also yielded fossils from these monstrosities, with another one of the largest members to exist, the Devincentia, actually hailing from Uruguay specifically. Then on top of that, it's also possible that this group even made their way to Europe and Africa, being represented by the Eleo Thorness and Lavocatavis. But with that said, I will mention that the classification of these two have come under scrutiny

in recent times. But as a wise man one said, when one door closes, sometimes another one opens. And this certainly applies here, as in 2024, a groundbreaking report found remains at Terabirds in what might be the unlikliest place of all, and that is, Antarctica, Seymour Island, to be exact. Now, to be fair, this unlikeliness really only applies to the present, as back in the day, before the Ice Age began, Antarctica was much warmer than present, and much closer to South America. And these two factors seem to have allowed for a couple of large Terabirds to hop on the Polar Express, so to speak, and thus increasing the range of this family occupied.

And across their range, the terror birds would interact and, well, terrorize, a massive trove of life, including an abundance of South American native ungulates, primates, rodents, cnarthens, reptiles, and even other birds. Yet none seem to admit a strong defense and slowing these guys down. And if we need any more proof that these guys were just built differently, then we only need to wait for what happened during the Pliocene, specifically the Great American Interchange, a war between two continents. And, uh, I actually made a video on this, so go watch that if you haven't. But as a short recap, this was essentially a biological war between South and North American

animals, wherein after the two continents linked up via Landbridge, animals from both sides swapped on over, causing major changes to the ecosystems, and in some cases, or rather many cases, leading to extinctions. And spoiler alert, South America got beat pretty bad, with many of its native animals dying out. While on the flip side, nearly none of them were able to successfully make its nature. North America, but some did, including the Titanus, a large terabird. In fact, it was this two-meter, or 6.6-foot genus, that was the only large South American predator to successfully establish a foothold in North America, with its remains coming from Texas and

Florida, where for millions of years it efficiently competed and co-existed with numerous North American predators, such as saber-toothed cats, canids, bears, and yet again, other birds, while also successfully hunting North American animals such as equids, northern rodents, endemic ungulates, and camels, because yes, camels come from North America. That being said, though the Titanus was able to succeed in the face of this event, the Great American Interchange is still viewed as an overall ding to the Terabird's dominance. In fact, it was even once thought to have played a large role in their demise, as the arrival of North American predators in the South was thought to have essentially triggered an unwinnable Battle Royale for the group.

But this idea is now more scrutinized, as while the arrival of small North American omnivores like the procyonids does align quite well with the population decline in southern terabirds, the actual arrival of large North American carnivores during the great interchange does not, suggesting that maybe these little buggers were really far more annoying, troublesome, and dangerous for the terabirds, perhaps because they ate their eggs. Additionally, what's strange is that the vast majority of terabirds were already seemingly dying out before North American animals even entered the scene, leading to a new idea that it was possibly a factor of multiple things that did them in, such as climate change earlier on and then later the competition.

In other words, after tens of millions of years of existence, the terabirds were finally dealt bad luck after bad luck. And while we do know that their fall from grace only happened recently, it's hard to say when these guys truly went extinct and what the final nail was for the group. And for a long time, it was actually thought that the Titanic, the North American Terabird, was really the last of them, the last survivor, so to speak. disappearing from North America about 1.8 million years ago. But we now know that didn't turn out to be the case, and we now know that much younger

terabirds showed resilience to the bitter end. With the youngest verified terabird for now being to have been the Brazilian Escatornis, a member dated to the late Pleistocene, who was believed to still be kicking as recent as 25,000 years ago. However, unlike its glorious ancestors, this guy had shrunk quite a bit, only weighing about 6.1 kilos or 13 pounds, indicating that the last survivor, might have shrunk compared to their earlier forefathers to survive. And what's interesting is that such a recent age found in a terabird has also

reignited the idea that maybe terabirds ended up meeting what is now the most dominant species in South America. In other words, modern humans. And while not confirmed, another promising leg bone belonging to an unidentified species indicates an even more recent expiration date of just 18,000 years, which, if accurate, would mean a fair chance that a kind really did meet the dinosaurs' comeback head on. And who knows, maybe that is where our love for chicken comes from. Thanks for watching, and until next time, on Extinctu.