Researchers have discovered evidence that monkeys arrived in North America 18 million years earlier than previously believed, according to a study published Wednesday in Nature.

And they were truly impressive monkeys indeed. The newly discovered Panamacebus transitus had to somehow cross the 100 miles of water that separated South America from North America prior to the formation of the Isthmus of Panama 3.5 million years ago.

As far as scientists know, the monkey is the only mammal to cross the Miocene Central American Seaway into North America. “We never would've predicted they would've been here,” study co-author Jonathan Bloch tells Nature.

While it's possible the monkeys swam to North America, it's more likely they inadvertently found themselves setting sail on rafts made of vegetation. Our current knowledge of Panamacebus transitus comes from seven fossilized teeth found at the site of the Panama Canal expansion, according to a press release.

The teeth are 21 million years old and show the new monkey likely resembled a modern-day capuchin. There's no evidence Panamacebus transitus did well in its new Panamanian home; the ancestors of modern-day North American monkeys came millions of years later after the isthmus was formed.

The Panama Canal expansion has been a boon for researchers. "I asked my boss for a million dollars to dig a hole in the ground," says one of the study's authors.

"Then the Panamanian people voted for the Panama Canal Authority to spend $5.6 billion dollars to expand the canal." (Some 10,000 human bones found in Germany may rewrite the history of war in Europe.)

This article originally appeared on Newser: North America's 1st Monkey Crossed a Sea to Get There

More From Newser