Ancient primates may have traveled from South America to North America about 21 million years ago — back when the continents were separated by 100 miles of water. The swashbuckling monkeys are reported in a study published Wednesday in Nature magazine.

“We never would've predicted they would've been here,” lead author Jonathan Bloch of the Florida Museum of Natural History told Nature.

Bloch and his colleagues identified seven monkey teeth encased in 21-million-year-old rocks in the the Panama Canal Basin. The teeth, which belong to a previously undiscovered capuchin-like species they have dubbed Panamacebus transitus, represent the oldest evidence of monkeys on the North American continent — and the first evidence of a mammal crossing the ocean that once separated it from South America.

The Isthmus of Panama — which connected what was once the island of South America to Central and North America — formed just 3.5 million years ago, at least according to most research. Until then, South America — where New World monkeys lived — was a long, watery trip away from our continent.

But the idea of monkeys rafting around unintentionally on beds of vegetation isn't as crazy as it sounds. To get to South America in the first place, monkeys had to cross over from Africa. Most scientists believe that happened about 40 million years ago. The Atlantic Ocean would have been a bit narrower than it is now, because of the way the continents have shifted, but it still would have been quite the trip. The monkeys in question were probably carried off to sea on uprooted trees after some kind of storm or other natural disaster.

The intrepid travelers that crossed to Panama didn't live to be the ancestors of modern monkeys in the region — those forefathers came much later, once the land bridge allowed mammals to move between continents with ease. And they didn't make it very far north, either, at least based on the lack of fossils throughout the continent.

At the time of the migration, Panama may have had plants quite similar to the ones the monkeys would have lived on in South America. "They found all the fruits and things they were used to eating,” Bloch told Science magazine. But as they moved farther north, they had to do without their favorite fruit trees.

“We hope to find more monkey fossils, but time is definitely a factor,” Bloch said in a statement. The expansion of the Panama Canal blasted through millions of years of rainforest growth, allowing Bloch and other paleontologists to excavate fossils that had previously been hidden. “We’re fighting against the forest that wants to grow over the rocks again. The expansion of the Panama Canal provides a once-in-a-century opportunity for these kinds of exciting discoveries. But we can’t assume we’ll always be able access these rock exposures," he said.

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