Monkeys first arrived in North America roughly 21 million years ago, according to examination of teeth discovered in the Panama Canal. These primates arrived on the continent following a major ocean voyage, researchers determined.

Roughly 21 million years ago, the continents of North and South America were separate bodies. At that time, a cadre of monkeys appears to have journeyed at least 100 miles across open ocean to reach their destination. If confirmed by further investigation, this discovery will push back the date when monkeys were known to walk the northern American continent.

Seven teeth belonging to members of the Panamacebus transitus species were found during excavations for an ongoing expansion of the Panama Canal. This variety of medium-sized primate was previously unknown to biologists.

As workers used explosives to blast away at rocks in the Las Cascadas Formation, paleontologists and other researchers quickly came in to collect fossils unearthed by the excavation.

"We suggest that Panamacebus was related to the capuchin (also known as 'organ-grinder' monkeys) and squirrel monkeys that are found in Central and South America today. Prior to this discovery, New World monkeys were thought to have evolved in isolation on South America, cut-off from North America by a wide seaway," said Jonathan Bloch of the Florida Museum of Natural History.

Until South America joined to its northern cousin 3.5 million years ago, animals on that continent evolved in extreme isolation from species on other lands. Before this recent find, the oldest known mammal migration from South to North America was a population shift of sloths between 8.5 and 9 million years before the modern day.

The newly-discovered species was named in honor of the location they were found, Panama, as well as their willingness to journey great distances.

Although the continents were separated at the time the monkeys made their journey, water levels were fairly shallow between the pair of bodies. This may have aided the primates in carrying out the journey to their new home. However, even given this fact, swimming 100 miles to North America would have been arduous task. One of the few methods by which this migration may have occurred would be if the monkeys built rafts out of vegetation, and floated north. Roughly 37 million years ago, monkeys undertook a similar journey from Africa to South America, biologists believe.

Discovery of the ancient monkey migration was profiled in the journal Nature.