Thanks to Brilliant for supporting this SciShow video!

As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. Why are there monkeys in South America?

This might seem like a strange thing to ask. But this isn’t some kind of philosophical, why is there anything at all, kind of question…which, I cannot help you with. The fact that we have monkeys in the Americas is much stranger than you’d think.

In fact, they shouldn’t really be on this side of the Atlantic Ocean, at all. They went fully extinct in the Americas, for millions of years, before they showed up again. So if they were gone for so long, how did they get back?

Well, what if I told you that they took a boat? [♪ INTRO] South American monkeys are members of a group called platyrrhines, also sometimes dubbed New World monkeys. And the funny thing about this whole mystery of platyrrhine parentage is, some of the very earliest primates lived in North America, but have no direct link to the South American monkeys today. One of those earliest groups of primates, called Teilhardina, appears in fossil records in Asia, Europe and North America pretty much all at once, around 56 million years ago.

And while there’s still a LOT of debate (that we’re not going to get into) over where they first originated, it looks like Teilhardina took one of a few possible paths around the world. They could have come from Asia and crossed over into North America via the Bering land bridge, then scurried over to Europe via the North Atlantic land bridge. Or, they could have originated in North America and traveled that same route, but in the other direction.

Despite being able to spread so far, those early primates went completely extinct in the Americas some time during the Eocene, around 35-40 million years ago, leaving us with no clear connection between those early primates and the South American monkeys we see today. So the discovery of a totally new, unrelated group of fossil primates in Santa Rosa, Peru opened the door to figuring out who these monkeys’ direct ancestors were. The researchers called this fossil species Perupithecus, and while there isn’t much fossil material of this species, what they do have gave them a solid clue about Perupithecus’s nearest relatives.

Who really aren’t all that nearby, geographically speaking. When researchers examined the teeth, they saw that they looked really similar to another fossil primate called Talahpithecus, which was found in Libya. You know, the Libya in Africa.

Like, across the Atlantic Ocean.. And by the time Perupithecus showed up, the land bridges that Teilhardina had used to continent-hop were basically gone, meaning they had no clear path to get there. But it gets even wilder.

It turns out Perupithecus’ ancestor wasn’t the only primate to show up in South America during the Oligocene. Recently paleontologists uncovered more teeth in Peru from a different group of now-extinct primates called parapithecids. And their teeth matched up to primate fossils from Egypt, representing another group of primates that came out of Africa.

By combining the anatomical information from the teeth with an analysis of DNA taken from more recent fossil teeth, paleontologists estimate that the parapithecid teeth were about 32 million years old. Paleontologists believe that both parapithecids and the early platyrrhines rafted over from Africa to South America somewhere between 35 and 32 million years ago. They may have even come around the same time!

So whatever way these primates managed to get to South America, they must have done it at least twice. And even though it makes logical sense that they just took the land route to get from Africa to South America, there’s really no evidence of that trek, unless they were some kind of paleo-Houdinis. For primates to get to South America by land, they would have had to travel across Africa, all the way across Eurasia, then over the Bering Strait and all the way down the North American continent to get to where they’ve been found in Peru.

And, they would have had to do all of this without leaving a single fossil in any of the places they traveled through. So traveling by land is probably out, which really only leaves us with the water route. And it seems like the best option that scientists can think of for how a bunch of primates crossed the ocean is that they took rafts.

To be clear, they were very likely not lashing together wooden beams to make a vessel, Castaway-style. It’s much more likely that these animals clung to clumps of vegetation, like mangroves or other fallen trees, that got swept out to sea during storms. Another theory is that they floated over on islands made from chunks of land that had broken off from the African shoreline.

And as wild as all this sounds, the conditions were actually pretty good back then for an ocean voyage. Sea levels at that time were lower than they are today thanks to the buildup of glaciers in the Antarctic. And, even though the continents weren’t linked up, they were closer together than they are today.

The distance from coast to coast right now is around 1,770 miles today, but at the time it would have been somewhere between 1,000 to 1,300 miles, which doesn’t sound like a huge improvement, but might have been critical for those little monkeys. Researchers estimate that the voyage across the Atlantic may have taken as little time as 10 to 13 days, and, while it wouldn’t be fun, most small mammals and reptiles are estimated to be able to survive that long without fresh food or water, in the right conditions. And also, researchers are pretty sure that the Africa-to-America trip wouldn’t have been the only time that primates have set sail.

For instance, we know that the lemurs of Madagascar are most closely related to primates on mainland Africa, but we also know that the lemur ancestors didn’t get to Madagascar until long after the landmass had broken away from the rest of Africa. That means they would have had to cross the Mozambique Channel somehow, and that somehow is probably rafts. Lemurs may have survived the journey by entering a state of physical inactivity called torpor, where their bodily processes slow down and their body temperature drops.

But not everyone is so convinced that rafting is how early monkeys made it to the New World. For one, just because we’re missing evidence of a land crossing, doesn’t necessarily mean that boats are the only answer. We just don’t have any evidence of what that other answer could be.

Right now the direct, concrete evidence for rafting is waiting to be found, a bit like sunken pirate treasure. And as Sherlock Holmes says, “When you have eliminated the impossible, whatever remains, however improbable, must be the truth”. And sometimes, the improbable truth is rafts.

Thanks to Brilliant for supporting this SciShow video! Brilliant is an interactive online learning platform with thousands of lessons in math, science, and computer science, including their course on Classical Mechanics. Now I know you might not naturally pair the spread of monkeys across the Earth with classical mechanics, but hear me out.

If monkeys traveled across the ocean, they’d need some kind of buoyancy to be involved, right? You’ll learn about buoyancy in the Newton’s laws section of classical mechanics. And the whole idea of travel Monkeys traveling from one place to another.

They could have done that using formula one cars, which are the first topic of the classical mechanics course, or rockets, which you’ll learn about in the fifth section of the course, or trains, which come up in the sixth section. Classical mechanics are all over transportation. And this Brilliant course can help you understand that stuff you might use regularly, like trains, and the stuff you only dream about monkeys using one day, like formula one cars.

It’s going to be so much more entertaining than the way they do it now! To get started on that journey, you can go to Brilliant.org/SciShow. That search will start you off with a free 30 day trial and 20% off an annual premium Brilliant subscription.

And as they say in our hometown, “Don’t forget to be awesome… just like those monkeys!” [♪ OUTRO]