The Mystery Behind the Biggest Bears of All Time

The Mystery Behind the Biggest Bears of All Time

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hey everyone Cali here with our new shirt that you can get at dftba.com link in the description it's comfy and nice and it's got a real pocket so if you'd like one go get it and help us out but now let's talk about some really big bears no like like really big bears in the cloud forests of the Andes lives a secretive little animal known as the spectacled bear the only native bear in South America with its distinctive marking small size and stout muzzle it's pretty unique looking as bears go and so
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are its habits it spends much of its time in the trees and unlike most other modern bears the spectacled bear feeds almost entirely on plants it turns out while this bear has some unusual traits it comes by them honestly it's the last surviving member of a subfamily called Trimark tane which includes the group of extinct bears commonly known as the short-faced bears the name comes from early researchers who thought that the Bears had short looking muzzles although today it's considered a misnomer in any case their snouts weren't their most
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distinctive quality a couple of the little spectacled bears ancestors were downright enormous for example in North America during the early Pleistocene epoch there was ark todas tzimmes standing on all fours a large member of this species would have been tall enough to look a full-grown person right in the eye in South America there was the amazing arctos cerium and gusted ins one specimen discovered in Buenos Aires in 1935 had upper arm bones that were twice as long as an adult humans and it would
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have stood more than three metres tall on its hind legs paws down it was the biggest bear the world has ever known the story of how these bears came to be and how they're related to the little plant-eating spectacled bear is an amazing tale about new frontiers rival creatures and continental drift in the face of each of these challenges the short face bears turned out to be remarkably adaptable undergoing radical changes in their diets and their body sizes to meet the demands of to changing continents and yet for reasons we don't
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quite understand their adaptability wasn't enough to keep them from going extinct [Music] the first short-faced Bears weren't big scary Giants in fact the earliest known genus a bear named PI own arctos was about the size of a small spectacled bear ply owned arctos first appears in the fossil record of north america about seven million years ago in the Miocene epoch and it's fossils have been found from coast to coast and some researchers think that it was the ancestor of all the trim ark teens that lived in the
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Americas it's descendants include the so-called lesser short-faced bear which first appeared around 2.5 million years ago and was about as big as the largest american black bears alive today and this supposedly lesser bear is thought to be the direct ancestor of the biggest bear that North America has ever seen the enormous Arcturus tzimmes it first appears in the fossil record roughly 1.6 million years ago it stood about 1.5 meters tall at the shoulder and the very largest individuals may have weighed
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more than a ton and not only was this animal big but it was widespread bones of our toda tzimmes have been unearthed at more than a hundred sites across North America from Ozark caves to the La Brea Tar Pits and from the banks of an Alaskan River to the wilds of central Mexico so it seems that ARCT Otis Simha stood pretty well for itself and some researchers have proposed that it might have been the ancestor to all the other giant bears found to the south South America's huge arctos cerium and gustin's this seems like it would make sense
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because you know for one thing they're both just unusually large but also while bears of some kind have been living in North America since the late Eocene epoch some 38 million years ago the fossil record shows that bears didn't arrive in South America until much later that's because South America used to be basically an island cut off from the rest of the world but around five or six million years ago a land bridge began to form between South America and North America and by about 2.6 million years ago in the late Pliocene epoch the
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connection was complete and the joining of these continents triggered a massive exchange of life called the great American biotic interchange suddenly species that were native to North America could travel south and vice versa so it's been argued that some of the big Arcturus bears of North have made the trek south and their descendants eventually gave rise to even bigger bears in South America with the earliest evidence of arctos cerium showing up in what's now Argentina about 1.75 million years ago but some recent genetic evidence suggests that South
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America's big bears actually came about in a totally different way in 2016 a team of researchers took DNA from a fossilized femur of arctos cerium and compared it to the genomes of both living and extinct bears and the results showed that arctos cerium was actually more closely related to the cute little and modern spectacled bear than it was to the giant Arcturus of North America so now it seems more likely that members of some other lineage of North American short-faced bears moved south and became the ancestors of octave theorem and the
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spectacled bear and if that's true then it means the mega bears of North America and those in South America must have acquired their huge body sizes independently and at different times so what evolutionary pressures would have driven each of these bears to start live and large well for arctos cerium and gusted uns it might have been a response to the strange environment its ancestors found in South America before South America met up with North America the continent was full of large herbivores like giant ground sloths and armored glyptodont and yet there were hardly any
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big predators sure there were the terror birds and the marsupial like hunter thigh lack of smileth and in the early Pleistocene the huge saber-toothed cats milodon moved in from the north but overall the first bears to colonize South America didn't face much competition so bigger bodies might have been better for the ancestors of arctos cerium and gusted ins allowing them to hunt or maybe scavenge some of the area's giant herbivores without much competition the giant bear could have easily established itself as a top predator or fearsome scavenger simply by
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virtue of its size but that doesn't mean that this bear was strictly a carnivore in 2009 researchers in Argentina compared the skulls of arctos cerium to those of living bears in search of clues about the ancient bears diet that's because modern bears did eat a lot of meat like polar bears tend to have smaller cheek teeth and longer jaws but in mostly herbivorous species you'll see the opposite shorter jaws and your cheek teeth and the skull of arctos cerium and gusted ins fell right in the middle it didn't look like a meat or
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plant specialist so the researchers figured that it was probably an omnivore much like many modern bears but in the same study other arc to cerium species landed in a different part of the spectrum their skulls looked a lot more like those of mostly herbivorous bears like the giant panda or the spectacled bear for reasons we don't fully understand the mighty arctos cerium and gusted UNS died out around 800,000 years ago and it seems that its lineage had gotten the memo that bigger was no longer better as time wore on arced Assyrian bears got smaller and their
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food habits became more herbivorous these descendants that lived between 800,000 and 12,000 years ago all weighed about 500 kilograms or less and by their skulls and teeth we can tell that they ate less meat the last and maybe smallest species was arctos cerium wing GI a bear that survived into the present Holocene epoch and may have been every bit as herbivorous as the spectacled bear so why did this lineage of bears change course in diet as well as body size it may be linked to a spike in competition remember when arctor theorem
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first appeared in south america it didn't have a lot of rival predators to deal with but by the late pleistocene the Jaguar the cougar and the direwolf had all crossed into South America so it could be that the descendants of the giant short-faced bear responded by downsizing and eating more greenery in order to avoid competing with these new predators now back up north and a bit farther back in time the evolutionary pressure to sidestep competition was also felt by North America's own giant bear market Otis tzimmes one of this
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bears more unusual traits was its long slender limbs which seemed to some paleontologists to be sort of cat-like so in the 20th century arced Otis tzimmes was typically seen as a fast-moving predator that pursued horses bison and other big game for long distances according to this view the bear wasn't just a hunter but a hyper carnivore an animal that overwhelmingly ate meat but in recent years closer inspection has shown that the Bears leg bones were probably too thin to support such a massive animal on long distance runs
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so an alternative model suggests that ARCT Otis was a scavenger that uses huge size to defend the carcasses it found and to frighten other carnivores away from their own kills this is a strategy known as klepto parasitism and it's also one of my new favorite word's but did this giant bear have an appetite for carrion it's certainly possible in Virginia art Otis fossils have been found alongside the remains of mammoths and on one mammoth anklebone there's a bite wound that paleontologists think was made by a short-faced bear but again
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this doesn't mean that ARCT oda tzimmes was a hyper carnivore or even a very strict one according to that skull study I mentioned before the morphology of the species resembles modern bears that eat a broad mixture of plants and meat in fact many specimens in California even have dental cavities which suggest they ate a lot of sugary plant foods like berries and honey so their diet may have varied by region with some populations eating more vegetation than others depending on factors like resource availability and interspecies
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competition but if the giant short-faced bears were so adaptable both in body size and in diet then why did they disappear our toda tzimmes disappears from the fossil record about 10,000 years ago and as with arctos area in the south no one knows why if this animal was really a hyper carnivore then its demise would be easier to understand as the big herbivores of the ice age died out the Bears would have been left with nothing to eat and the disappearance of Ice Age megafauna may have still played some role but so might the competition
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from modern Bears brown black and polar bears all members of the genus Ursus had each evolved and were roaming North America by the mid Pleistocene so the reasons behind the decline and fall of Arcturus and the abrupt disappearance of arctos cerium and gusted ins and it's descendants remain something of a mystery today only the spectacled bear remains forging away in the Andes on its furry shoulders rest the legacy of those goliaths of the recent past the true mark teens thanks for joining me today in the
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Konstantin Haase studio and an extra big thanks to our current Yount ologists Jake Hart John Ivy John Davison and Steve if you'd like to join them in our other patrons in supporting what we do here then go to patreon.com/crashcourse [Music]

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