[♪ INTRO] [Squeaks squeaking] Oh hey, Squeaks! What are you doing? [Squeaks squeaking]
Oh, I see! You’re looking at a map. Squeaks has been learning about
animals that lived a long time ago. Creatures like the giant woolly
mammoth or the saber-toothed Smilodon. Now he’s trying to picture
the places where they lived. A map is a great way to do that, Squeaks! A map shows us pictures of
the land all across the Earth. We can see the green and
brown parts that are land, and the blue parts that a
re water. Say, do you know where the Fort is on this map? [Squeaks squeaking] We’re here in North America. North
America is one of Earth’s continents. Continents are Earth’s big pieces of land. Most people say we have seven continents:
Australia, Africa, Antarctica, Europe, Asia, North America, which we’ve just seen, and South America, which is right here. [Squeaks squeaking] You’re right, that skinny piece
of land does look kind of like a bridge connecting North
America to South America. An
d it kind of is a bridge, made of land! That skinny little land bridge
is one of the reasons that we see all the cool animals we do around the
Fort, like foxes and even mountain lions! [Squeaks squeaking] Here, let me explain how one tiny piece
of land gives us so many cool creatures. About 65 million years ago,
when the dinosaurs went extinct, North and South America looked like this; they weren’t touching and
there was no land bridge. There were certain animals in North
America and other
animals in South America. And unless they were really
good fliers or swimmers, and could cross a lot of ocean…
that’s where they stayed. But then things changed. A continent is a huge, heavy
piece of land, but it can move! [Squeaks squeaking] Oh, you’d like to see them have
a race to see who’s fastest? Well, you’d be watching quite for a while. Continents move so slowly that you or
I would never notice the difference, even if we watched our whole lives. [Squeaks squeaking] It’s very very s
low. But verrrryyyy sloooowwwwwly, over a very long time, changes can happen. North and South America
moved close enough together for that little land bridge to form. And when that happened, things
began to change in both places! Animals did what animals will do: they moved around looking for
things like food and places to live. About 3 million years ago, some of
the animals in North America moved over that skinny piece of land
into South America and some animals in South America crossed in
to North America. This switch was so important that scientists gave this movement a name: the
Great American interchange. [Squeaks squeaking]
Right, an interchange. That word just means the animals on
the two continents swapped places; some went North to South,
and some went South to North. [Squeaks squeaking] Animals that moved from North
America to South America included ancient kinds of foxes, horses, llamas,
and big cats like jaguars and pumas. Bears moved across the bridge
into South
America, too. Big ones. Much bigger than
even our biggest bears today. When standing on all four
legs, the short-faced bear was about as tall as an average grown-up. If they stood up on two legs, they were
about as tall as an African elephant! [Squeaks squeaking] It would be cool to see one,
but unfortunately we can't, because these huge bears became extinct. That means they died out, so
they’re no longer around today, like the dinosaurs or saber-toothed cats.
[Squeaks squeaking] Oh, good
question! Squeaks wants to know how we
know these animals existed. We know these ancient animals
lived in South America because we’ve found fossils of them there. Fossils are traces left
behind by ancient creatures, either body parts like bones and teeth, or
other signs like footprints and even poop! Fossils also give us a good idea
of what these animals looked like. For example, they showed us that the snouts on short-faced bears were shorter than
the snouts on bears we see today. Shorte
r than on most bears, anyway. Because one cousin of the short-faced bear
still exists. And guess where they live? [Squeaks squeaking]
Oh, yeah, that’s all right. South America! These animals, called spectacled bears, are much smaller than their ancient
relatives but they still have a short snout! They are probably related to
the large short-faced bears that crossed the land bridge into South America. [Squeaks squeaking] Good question, Squeaks: what about
animals that went the other way? Ther
e were some giant animals that made the trip from South America to here in North America. Glyptodonts were a lot like giant armadillos. Some kinds were over 4 meters long,
about half the length of a school bus, and weighed as much as a rhinoceros. They had a hard shell that looked like a turtle shell and other bony
parts that acted as armor. [Squeaks squeaking] Yeah! I can’t imagine carrying so
much armor around all the time! Another animal that moved as part of the Great American Interchange
were the giant sloths. [Squeaks squeaking]
I love sloths too. They’re super adorable with the way they
hang upside down and move so slowly. The sloths we see today are less than a meter long and spend almost
their entire lives in trees. But the sloths that moved into
North America millions of years ago were about the size of elephants! They were too large and too
heavy to hang out in trees. Instead, they walked on the ground, using their huge claws to knock down
branches and dig up roots t
o eat. [Squeaks squeaking]
Yes, these animals are also extinct. About 10,000 years ago, they
got some new neighbors: humans. Some scientists think that humans
might have hunted some of the sloths and Glyptodonts because they needed food. Scientists also think that big
changes in Earth’s temperature and weather made it too hard for some
animals to find food and places to live. [Squeaks squeaking]
I know! I’d like to meet a giant sloth too. But at least thanks to fossils,
we know a little bit
about them! And it’s so amazing that thanks to the
super slow movements of continents, we got to see all of these
animals live in brand new places. I have an idea! Let’s look up some museums online and see if any of them have
exhibits about giant sloths. Thanks for joining us! If you want to have
fun with me, Squeaks, and all our friends, you can subscribe to SciShow Kids, and
we’ll see you next time here at the Fort! [♪ OUTRO]
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