It was 1977, and a farmer was plowing his
field on a plateau high in the Andes mountains, near a Colombian village called Villa de Leyva,
when he stumbled upon a giant fossilized skeleton. The specimen was about 7 meters long, but
it was missing the tail, so the actual animal would’ve been close to 11 meters. And this wasn't the first time that fossils
had been found near this village; go a bit in any direction and you're bound to come
across one. Locals have even found fossils of so many
ammonites that they’ve embedded them in the walls of their buildings as decorations. But this time, the fossil skeleton was of
a giant marine reptile known as a pliosaur. More specifically, these were the remains
of a Kronosaurus. Weighing up to 12 tons with around 24 pairs
of teeth, these pliosaurs looked like some sort of terrifying cross between a dolphin
and a crocodile. And Kronosaurus swam the seas of the Early
Cretaceous Period, between 125 million and 100 million years ago, from South America
to Australia. Now, sure, sea levels were higher in the Cretaceous,
because temperatures were warmer and there was no ice at the poles. But sea levels weren’t 2150 meters higher,
which is the altitude at which Villa de Leyva sits today. So, how did this giant marine reptile end
up high in the Andes Mountains? It required a major change to the face of
the planet -- one that took place over millions of years and radically altered the South American
continent and everything on it, to this day. Kronosaurus first showed up around 125 million
years ago, when much of northern South America was underwater. And it, along with its pliosaur relatives,
was probably terrifying to most of the things it shared the seas with. Pliosaurs were top marine predators in their
day, filling a niche similar to predatory whales and crocodiles today. And the largest are considered to be the Tyrannosaurus
rex of the seas. In fact, Kronosaurus was named after the ancient
Greek titan Kronos, who ate his own children for some reason, because there’s evidence that these pliosaurs
ate other members of their own genus. Now, pliosaurs are a type of plesiosaur, an
extinct order of marine reptiles, and it seems that they also hunted other plesiosaurs as
well as turtles, ammonites, and basically anything that was smaller than it was. But the local waters that these pliosaurs
lived in were about to change. South America was once connected to North
America, Africa, and Antarctica as part of the supercontinent known as Pangaea, which
started breaking up around 200 million years ago. But since the end of the Jurassic, the South
American plate of that whole landmass had been moving westward. And about 140 million years ago, it ran into
a smaller plate that was moving eastward. This was the Nazca plate. The collision caused the edge of the Nazca
plate to get pushed under the South American plate, in a process called subduction. And the subduction continued through the extinction of Kronosaurus, and later, that of all of
the plesiosaurs at the end of the Cretaceous. Meanwhile, on land, the survivors of the End
Cretaceous extinction event were carrying on. The region known today as the Amazon was already
covered in rainforests and criss-crossed by rivers. And fossils show that marsupials and ungulates were abundant, as were crocodilians. Then, under the feet of those animals, bigger changes started to take place. Around 45 million years ago, the denser parts
of the Nazca plate started to sink under South America faster than the lighter parts did. This started the first of what would be several
growth spurts that created the Andes. And it would have some major effects on the
land and life around it. For one thing, as the Andes started their first growth spurt, they formed barriers to
the rivers in the Amazon that had once flowed west into a shallow sea. And by the time another growth spurt started,
around 25 million years ago, the newly formed mountains blocked moisture from traveling
across the continent from the Pacific and Atlantic. Instead, that moisture fell as rain on the
Andes, washing sediments down into the Amazon. This eventually caused much of northern South
America to become a giant wetland, fragmenting the former forest. And in these new swamps, aquatic life flourished, like mangrove trees, more crocodilians, and
even one of the largest turtles that ever lived. Meanwhile, newly formed connections with the
Caribbean Sea brought marine life, like dolphins and rays, to the heart of the continent. As the mountains continued to rise, even more sediments were carried into the Amazon. And by 7 million years ago, they provided
fertile ground for a renewed rainforest that replaced the swamps. Now this coincided with other big environmental changes in the Miocene Epoch, like global
drops in sea level and temperature possibly caused by changes
in Earth’s orbit. And together, these changes were too much
for many of the animals that had once thrived there, like the giant turtle and a lot of
the marsupials. By around 6 million years ago, the Amazon
River and Rainforest looked pretty similar to what we see today. At last, it was time for the final push -- the one that raised the plateau that includes
Villa de Leyva, where all those fossils are found. Up until this point, the land in that area
just wasn’t as tectonically active as the rest of the mountain chain. But during this final pulse, the activity
was so intense that it eventually lifted up this area too, resulting in a high, flat plateau
within the mountains. And so, the land underlying this village had
gone from being underwater to sitting at 2150 meters, bringing Kronosaurus and all the other fossils buried with it to new heights. And the formation of the Andes had a huge
impact on the plants and animals in South America. For one thing, it created a type of ecosystem
that’s only found in the Andes and in Central America: an ecosystem called a páramo. Páramos form between around 2800 and 4800
meters above sea level in humid alpine regions of the western hemisphere. And they consist mainly of grasslands and
other hardy plants, as well as animals that have been able to adapt to this extreme environment. But since these ecosystems reached their current
heights about 2.7 million years ago, changes in global temperatures have caused the boundaries
of paramos to shift, too. This has effectively turned individual páramos
into islands, driving the evolution of thousands of species that aren’t found anywhere else
on Earth, like a strange and rather handsome hummingbird known as the buffy helmetcrest. These habitats are also seasonal homes to some mammals, like the spectacled bear: the
only bear species in South America. There are even species of lizards that give
birth to live young, rather than laying eggs -- an adaptation that provides the embryos
with warmth and protection until they’re born, rather than leaving the eggs out in
the cold. And, we can’t forget about the world’s smallest and most adorable deer, the northern
pudú! The ancestors of many of these species are
thought to have lived in these habitats before they became elevated, later diversifying in
relative isolation as the Andes rose up. So, the Andes Mountains--the backbone of South
America-- were shaped by the movement of the planet’s tectonic plates, and have, in turn,
completely changed the face of the land and life there today. From the remote paramos to the Amazon Rainforest these ecosystems are only possible because of the
formation of the Andes. And, they explain how a giant marine reptile
ended up on a mountaintop. And who knows? there are probably many more reptiles, both
living and extinct -- like my boy Kronosaurus -- that are still waiting to be discovered
there. Thanks to this month’s Eontologists for
helping us reach new heights: That pun is courtesy of Kallie. You can thank her for that. Lucan Curtis-Mahoney, Sean Dennis, Jake Hart, Jon Davison Ng, Patrick
Seifert, and Steve! Do you enjoy watching me suffer through Kallie’s
puns? Have you ever thought you could do better? Well now’s your chance! Patreons that support at the $10 level can
submit jokes and puns related to national history. The Eons team will choose one per episode
and the hosts will have to read them cold! Become an Eonite at patreon.com/Eons and send
us your jokes! I can't wait to see them... And thanks for joining me today in the Konstantin
Haase studio. Subscribe at youtube.com/eons for more adventures
in deep time!
I hate to say it, but this is probably my least favorite episode from them. It’s not really inaccurate, just boring. They squandered what could have been a cool episode about Pliosaurs, instead opting to explain how the Andes rose. Kronosaurus deserves more than a 2 minute spiel.
I liked the episode