(host) 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 have 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 look 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 2,150 meters higher, which is the altitude at which Villa de Leyva sits today.

So how did this giant marine reptile end up so 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 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 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 with rain forest and crisscrossed 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 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 seven 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 changes in sea level and temperature possibly caused by changes in Earth's orbit.

And together, these changes were just too much for many of the animals that had once thrived there, like the giant turtle and a lot of the marsupials.

So by around 6 million years ago, the Amazon River and rain forest look 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 2,150 meters, bringing Kronosaurus and all the other fossils buried with it to new heights.

And the formation of the Andes has 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 in Central America, an ecosystem called a páramo .

Páramos form between around 2,800 and 4,800 meters above sea level in humid Alpine regions of the Western Hemisphere, and they consist mostly 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 páramos 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 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 pudu.

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 páramos to the Amazon rain forest, these ecosystems are only possible because of the formation of the Andes.

And, of course, 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.

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