ExtinctZoo - The Bear That Was As Large As The Allosaurus

Episode Date: March 5, 2024

Through old studies and numerous paleo media depictions, the Andrewsarchus has gained a reputation of being the undisputed largest mammalian land predator and carnivore ever. However, this is almost 100% not the case, as another lesser known mammal has a much more solid claim to the throne, Arctotherium sometimes known as the giant short faced bear

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Co-Pilot handles the spreadsheets. Learn more at M365Copilot.com slash work. Extinct animals have long been a source of fascination for many, and non-avian dinosaurs in particular have drawn great interest thanks to their huge and daunting sizes. Through the years, much debate has occurred around this topic, especially about which predatory dinosaur was the biggest to ever live. Meanwhile, terrestrial mammalian carnivores have gotten much less attention on their sizes, perhaps since mammals are still around or because they never attain the sizes of dinosaurs. On top of this, when people finally do discuss this topic,

there is one extinct animal that is almost always the first one to be named, and without much argument at that. This is the Andrew Sarkas. Most believe that this strange carnivore is the undisputed king of mammalian predators on land. And yet this isn't actually the case, as most sides actually point to another lesser-known predator taking this crown. The Arctotherium. While this beast's true size has only been revealed in the last few years,

its existence has been known for far longer, with remains first being unearthed over 170 years ago in Argentina. The original specimen was not as large as later ones, but it was still big enough to turn a few heads. Its fossils were also an excellent condition, allowing paleontologists to quickly determine that it was a new kind of bear, which along with its bulkier build led to it being named the Arctatherium, meaning the bear beast.

It was also given the species name Bonnerience, a nod to the city in which it was originally located. The exceptional nature of its bones didn't only help paleontologists figure out it was a bear, but it also allowed them to further place it as a member of a specific family, the Tramarktonae family. This was thanks to its uniquely shaped skull, which was heavily deepened, giving off the illusion of being short.

This is a feature seen in all Tramarktonae and has led to them being nicknamed the short-faced bears. Currently, there are four known genera in this group, only one of which is still living, the spectacled bear. The group is perhaps best known not for the survivor, but for the extinct member, Arctodus, a giant bearer that is often considered one of the largest mammalian hunters to have walked the earth.

And a giant it was, with large males clocking in at 2,100 pounds or 950 kilos, making it about the same size as the largest recorded polar bears, and just shy of the Andrew Sarkas, which currently is thought to have weighed no more than one ton. The large nature of the arctodus also made it bigger than the arctotherium Bonad. which is believed to have weighed a maximum of 500 kilos or 1,100 pounds. But its inferiority to Arctodus would not last forever, as since its discovery, other species of this mighty beast have been described, with five being known today.

This includes the Angustrians, Bonariense, Tarijense, Vitustum, and Wingay. All these species of Arctotherium were unique in when they existed. and their dentition. However, the biggest difference among them all was their sizes, as one in particular completely dominated the others when it came to stature, the Angustodans. This is by far the most well-known species of Arctotherium, and rightfully so as it was an absolute Titan,

the likes of which may have never been seen before. Originally, paleontologists believed that this species grew to be between 400,000, 410 and 1,200 kilograms, or 910 or 2,600 pounds. At this size, it was a contender for being the largest bear of all time, but not a contender for the title of biggest mammalian land predator overall. However, the short-faced bears, including the remaining member, are well known for having a high level of variety and size amongst individuals, especially between genders, with males sometimes being 50% larger than females.

This fact also extended to the Arctatherium, and thus, over the years, dig teams have occasionally found massive male Angustodans that pushed the envelope of how large terrestrial mammalian predators could get. And this all came to a climax in 2011, when a specimen located in Buenos Aires blew everyone away. The individual in question had a giant, and humorous radius in Ulna, which based on their measurements led scientists to believe that

this bear potentially weighed a staggering 4,500 pounds or 2,040 kilograms. In other words, over two tons. At this weight, it even outweighed some well-known large theropods, including the average adult allosaurus, and was thrice the weight of the biggest known serratosaurus. However, the paleontologist who estimated this size was wary of this large number and believed that a more likely weight for this Titan was 1,760 kilograms or 3,600 pounds. If this is true, it would still make the Arctotherium significantly larger than any terrestrial mammalian predator today, and a tad bit heavier than the extinct Sebacid Burinusukas. This is monumental, as the Burinusucas is widely concerned.

considered the largest terrestrial predator to have lived since the dinosaurs. Additionally, this Arctatherium specimen wasn't just a giant when it came to weight, as it was extremely tall as well, reaching 14 feet or 4.3 meters when standing upright. At this height, it was taller than both the average T-Rex and large African elephants. Its considerable stature also resulted in paleontologists starting to refer to it as the giant short-faced bear, A nickname it now shares with Arctodosimus. The source behind its gigantism is believed to have stemmed from the extinction of the Chapal Malania, a highly specialized omnivore that had a diet very similar to that of modern bears,

especially the spectacle bear. This may have created intense competition and thus with it gone, the Arctitharium was able to swell in size within a very short period, allowing it to become the largest predator around during the early Pliocene and early Pleistocene. And with this useful trait on its side, the Arctatherium became a killer of giants. As carbon isotope studies show that it had a preference for consuming large quantities of meat,

specifically flesh that came from horses, tapirs, camelids, macrockinids, glyptidants, giant ground sloths, toxodontids, and gomphitheers. The location of damage found on these herbivores, coupled with the discovery of crack and worn teeth amongst the Arctatherium, implies that it both scavenged and actively hunted these animals, typically delivering death by using its large canines to bite the neck and back of prey with bone-crushing force, while also using its large robust forepaws to deal additional damage.

And despite its outward appearance of being quite cumbersome, the Arctatherium Angustodans was actually surprisingly efficient at catching these animals thanks to its proportionally long legs that granted it a high running speed, which may have even exceeded 40 miles or 60 kilometers per hour, making it about as fast as a grizzly bear, which is significantly lighter. It also had adept senses like smell,

that it could use to help it capture prey as studies on the structure of its skull indicate that it had a powerful nose that could pick up scents multiple miles or kilometers, away. However, despite possessing quite the arsenal, the giant short-faced bear wasn't just simply a bloodthirsty predator. As denticians suggests that it was ultimately an omnivore, that would consume fleshy roots,

fruits, berries, grasses, and forbes when the chance arose. This diverse diet, along with its size, granted yet another advantage over its competing predators, consisted of the Smilodon, Theriodictus, Canis, Proto-Sion, Jaguars, and Cougars. Some of these contemporary carnivores like the Smilodon were somewhat comparable in size, but not big enough to pose a serious threat to large adult bears, if alone. This allowed the giant short-faced bear to reign supreme in its home of Argentina and possibly El Salvador and Bolivia as well. Within these lands, located specimens showed this giant had a preference.

for open plains, but would venture in forested areas as well. Rare finds further implied that the Arctatherium would occasionally inhabit Paleo Burrows, in which multiple bodies have been found leading to the hypothesis that this bear may have prowled the lands in familial groups. Despite showing an aptitude for burrows, it's not believed to have created them. Rather, it's agreed that the Arctatherium was a conqueror of Burroughs that were dug by various Xenarthens. These burrows proved to be a big part of this bear's life and was even a source of competition and conflict amongst individuals. Such battle for burrows occurred often enough

that paleontologists believed that this bear alone was accountable for an exponential increase seen in the number of paleo burrows during the early paleocene, as constant takeovers forced Xenarthans to regularly evacuate and start over assuming they weren't killed. These fights were quite vicious in nature, often leading to deep injuries that were prone to infection. However, burrows alone were not the only source of conflict amongst this species, as adults had a high level of damage in their skeletons, suggesting a life of violence.

Some even believe that the high percent of cracked teeth seen in this bear is partially attributed to fights with other individuals. This tough lifestyle may have been a considerable source to mortality amongst adults and sub-adults, But this didn't stop this giant. What did, though, was the ecosystem itself. As the early Pleistocene ended and the middle Pleistocene began, the Carnivore Guild, aka the group of carnivore species that shared the habitat and competed for the same resources, started to diversify and mature, creating new changes and challenges for the Arctatherium.

Eventually, it stopped growing in size, and then it slowly started to disappear. until 700,000 years ago, when the Arctatherium Angostodans fully vanished. This spelled the end for the giant stage in the Arctatherium's existence, but not its entire story, as the Angostodon's legacy lived on in four new smaller, medium-sized species that emerged. This shrinkage was quite surprising, as in America where the Arctodotus was located, its descendants got only bigger as time progressed, not smaller. However, ultimately the size decrease would work in the favor of the Arctotherium, as these newer species would end up outlasting the Arctodus by thousands of years. These four species could be divided into two distinct categories, with one group being the Arctotherium that did a complete 180, shifting from being mainly carnivorous to highly herbivorous.

This included the Vitustum and Wingay, which were also the smallest Arctotherium species. Studies on their isotope levels show they specialized in C3 vegetative material, like fruits and leaves, but on occasion would still consume meat as indicated by spikes in their isotope levels. These rare meat snacks are believed to have come from the ground sloth, no-throetherium, and possibly through cannibalism as well. This overall switch in diet is believed to have been due to their more northern range, which brought them into contact with many of the great American interchange predators. creating high and fierce competition, forcing them to adapt to a different diet.

Some of these carnivores on the scene included American lions, dire wolves, gray wolves, coyotes, and the Smilodon Fitalis. Despite the primarily herbivorous diet taking pressure off competition with large predators, Duingay and Vitustam now had to compete with smaller omnivores, presenting a whole new set of challenges. While this was going on, their southern counterparts, the Bonarience and Tarihense had retained the giant Arctatherium's preference for consuming meat. This was made possible due to their more southern range of Chile and Argentina, meaning they did not have to worry as much about the Great American Interchange. Of the two, Arctithium Tarigence was smaller, being about 20% lighter than the Bonnerianse, but both had very similar diets, which consisted of animals' range.

ranging between 100 kilograms or 220 pounds, and 300 kilograms or 661 pounds, meaning that small to medium-sized camelids and horses were the main parts of their diets. It's also believed that these two practiced higher levels of scavenging and bone consumption than their giant predecessor in order to supplement their urine for meat. As unlike the Angustodans,

the Arctotherium were not the largest animals around and therefore could not tackle every prey in their environment, resulting in them leaving adolescent and younger megafauna to bigger predators like giant jaguars and the Smilodon. Other competitors that were around the time that further created pressure included large canids and even each other. Ultimately, though, despite being smaller, the diverse diets of these new Arctatherium proved highly successful, and they continue to thrive for another 691,000 years following the demise of the large Angustodans, until they too eventually vanished. Dated specimens show that the four went extinct

between 12,000 and 9,000 years ago, with Winge holding on the longest in parts of Venezuela. What's fascinating is that they all died out around the exact same time, despite inhabiting different areas and possessing varied diets, leading to numerous questions regarding why it went extinct. While it's hard to pinpoint the exactness of its demise,

paleontologists have pointed out, that the quaternary extinction event, for whatever reason, was exceptionally rough on bears, especially those that did not have conservative morphologies, meaning that the abnormal, robust structure and relatively elongated limbs of arctatherium, which are not typically seen in other bears, may have played a substantial role in its inability to adapt to a changing world, bringing a final end to what was once the largest mammalian predator. Ambition comes in all shapes,

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