Hey everyone, Kallie here with our new shirt
that YOU can get at DFTBA.com, link in the description. It’s comfy, nice, and this
is a real pocket! So, if you’d like one, go get it and help us out!But now, let’s
talk about some big bears… no, 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 markings, small size,
and stout muzzle, it’s pretty unique-looking as bears go. And so 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 that, while this bear has some
unusual traits, it comes by them honestly. It’s the last surviving member of a subfamily
called Tremarctinae, 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 distinctive quality. A couple of the little spectacled bear’s ancestors were
downright enormous. For example, in North America during the early Pleistocene Epoch, there was Arctodus simus. Standing on all fours, a large member of this
species would’ve been tall enough to look a full-grown person right in the eye. And in South America, there was the amazing
Arctotherium angustidens. One specimen, discovered in Buenos Aires in 1935, had upper arm bones
that were twice as long as an adult human’s and would have stood more than 3 meters 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-faced bears turned out to be remarkably adaptable, undergoing radical changes in their
diets -- and their body sizes -- to meet the demands of two changing continents. And yet, for reasons we don’t quite understand,
their adaptability wasn’t enough to keep them from going extinct. The first short-faced bears weren’t big,
scary giants. In fact, the earliest known genus--a bear named Plionarctos--was about
the size of a small spectacled bear. Plionarctos first appears in the fossil record
of North America about 7 million years ago in the Miocene Epoch, and its fossils have
been found from coast to coast. And some researchers think that it was the
ancestor of all of the Tremarctines that lived in the Americas. It descendants included 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
Arctodus simus. It first appears in the fossil record roughly
1.6 million years ago. It stood about 1.5 meters at the shoulder and the very largest
individuals may have weighed more than a ton. And not only was this animal big, but it was
widespread. Bones of Arctodus simus 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 Arctodus simus did pretty
well for itself. And some researchers have proposed that it might have been the ancestor
of the other giant bear found to the south -- South America’s huge Arctotherium angustidens. This seems like it would make sense. Because,
for one thing, they’re just both unusually large. But also, while bears of some kind had 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 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
Arctodus bears of North America made the trek south, and their descendants eventually gave
rise to even bigger bears in South America, with the earliest evidence of Arctotherium
showing up in what’s now Argentina about 1.75 million years ago. But, some recent genetic evidence suggests
that South 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 Arctotherium and compared it to the genomes of both living and extinct
bears. And the results showed that Arctotherium was
actually more closely related to the cute, little, and modern spectacled bear than it
was to the giant Arctodus 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 Arctotherium and the 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 living large? Well, for Arctotherium angustidens, 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 glyptodonts. And yet, there were hardly any big predators.
Sure, there were the terror birds, and the marsupial-like hunter Thylacosmilus. And in
the early Pleistocene, the huge saber-toothed cat Smilodon 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 Arctotherium angustidens, allowing them to hunt -- or maybe scavenge
-- some of the area’s giant herbivores. Without much competition, the giant bear could’ve
easily established itself as a top predator or fearsome scavenger simply by virtue of
its size. But that doesn’t mean that this bear was
strictly a carnivore. In 2009, researchers in Argentina compared
skulls of Arctotherium to those of living bears, in search of clues about the ancient
bear’s diet. That’s because modern bears that 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 bigger cheek
teeth. And the skull of Arctotherium angustidens
fell right in the middle. It didn’t look like a meat or plant specialist, so the researchers
figured that it was probably an omnivore, much like many modern bears. But in the same study, other Arctotherium
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 and the spectacled bear. For reasons we don’t fully understand, the
mighty Arctotherium angustidens 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, Arctotherium bears got smaller,
and their 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
Arctotherium wingei, 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 Arctotherium 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 dire wolf 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: Arctodus simus. One of this bear’s more unusual traits was
its long, slender limbs, which seemed to some paleontologists to be sort of cat-like. So in the twentieth century, Arctodus simus
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 hypercarnivore, an animal that overwhelmingly ate meat. But in recent years, closer inspection has
shown that the bear’s leg bones were probably too thin to support such a massive animal
on long-distance runs. So, an alternative model suggests that Arctodus
was a scavenger that used its huge size to defend the carcasses it found--and to frighten
other carnivores away from their own kills. This is a strategy known as kleptoparasitism,
and it’s also one of my favorite words! But did this giant bear have an appetite for
carrion? It’s certainly possible. In Virginia, Arctodus fossils have been found
alongside the remains of mammoths. And on one mammoth ankle bone, there’s a bite wound
that paleontologists think was made by a short-faced bear. But again, this doesn’t mean that Arctodus
simus was a hypercarnivore, or even a very strict one. According to that skull study I mentioned
before, the morphology of this species resembles modern bears that eat a broad mixture of plants
and meat. In fact, many specimens from California even
have dental cavities, which suggests that 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 inter-species competition. But if the giant short-faced bears were so
adaptable, both in body size and in diet, then why did they disappear? Arctodus simus disappears from the fossil
record about 10,000 years ago. And, as with Arctotherium in the south, no one knows why. If this animal really was a hypercarnivore,
then its demise would be easier to understand: as the big herbivores of the Ice Age died
out, the bears would’ve been left with nothing to eat. And the disappearance of Ice Age megafauna
may still have played some role. But so might the competition 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 Arctodus, and the abrupt disappearance of Arctotherium angustidens and its descendants
remain something of a mystery. Today, only the spectacled bear is remains,
foraging away in the Andes. On its furry shoulders rests the legacy of those goliaths of the
recent past -- the tremarctines. Thanks for joining me today in the Konstantin
Haase studio! And extra big thanks to our current Eontologists, Jake Hart, Jon Ivy,
John Davison Ng and STEVE! If you’d like to join them and our other
patrons in supporting what we do here, then go to patreon.com/eons and make your pledge! If you enjoyed this tale of the short-faced
bear, then you should check out our episode on another epic animal: the bone-crushing
dogs!
WHY WOULD THEY MAKE T-SHIRTs WITHOUT DINOSAURS ON THEM???!
So this was a disappointing thing to learn. See, I always thought that bears in South America only occur in the North West because the geography further south was too challenging for any kind of bear. And further south you have Chile, my country, which is basically North America's West Coast upside down: Though the first third is currently the driest desert, the other two thirds are biomes where bears would thrive.
But then you find out that bears occured in Argentina. And though the Andes pose a mostly impenetrable wall (even back then), but in the south and Patagonia there are plenty of lower mountain passes and flatter areas where some bear populations could've made their way across that divide, but it never happened. And thus, we never had awesome bear species occuring in Chile.
Sure, they would've probably been driven to near extinction once the Chilean State started occuppying the deep south, but still, it would've been amazing to have Chilean bears is what I'm saying.
(reposted from YouTube btw)
Don’t tell Stephen Colbert...