The evolutionary mystery of how monkeys arrived in South America may have been solved. New fossil evidence collected by Ken Campbell and his team indicates that monkeys came to the New World from Africa. “One of the teeth is very, very similar to a fossil tooth from Africa,” Campbell, a curator at the Natural History Museum of Los Angeles, told “In paleontology, when the specimens that you have look very similar then that’s a general indication of comparable ancestry. So the fact that these two teeth are very similar suggests - not prove, but suggests  - that there might be a relationship between them.”

An island continent for millions of years, South America has seen a variety of creatures somehow arrive to its shores, according to fossil records. However, the evolutionary history of monkeys on the continent has remained a mystery, the general belief among researchers being that the monkeys somehow managed to journey across the Atlantic from Africa. Until now, there was little evidence to back this theory.

“The general hypothesis is that - first of all, these monkeys were very small,” Campbell said. “They’re about the size of a small squirrel with a long tail. So they’re very small and as a consequence their food and water requirements would be much less than if they were very large. So the general hypothesis is that there were monkeys on a river bank. During flood season, trees get swept into the river and carried out to the ocean. As vegetation rafts, [the trees are] carried across on the Atlantic based on wind and current directions. This remains a hypothesis- there’s no proof yet, although the similarities between the monkeys suggests that it did happen.” The fossils show that the monkeys arrived on the continent at least 36 million years ago. Previous fossil records dated the monkey’s arrival back at 26 million years.

The fossils were discovered along a riverbank in the east Peruvian Amazon, a notoriously challenging place for researchers to work. According to Campbell, “The Amazon is a bit of a difficult place to work because there are no outcrops to speak of because they’re all covered by forest. And so the only outcrops that one finds are along riverbanks, and that means that you can only look for fossils during the dry season, when the rivers are at their lowest point.” The fossils were discovered in 2010, but it wasn’t until 2012 that Campbell realized they belonged to a primitive monkey. “Finding primates was a possibility, but they are very rare and very small,” he said. “So yea, in the end, it was a surprise.” Campbell has been working with a team of Argentinian paleontologists to scour the Amazon with the hope to unlock the mysteries of its evolutionary history. One of the most biologically diverse areas on the planet, the region holds many secrets that researchers have yet to discover. Campbell and his team are hoping to change that.  “I’ve worked in the Amazon for many, many years - a lot of it dedicated toward looking for fossils and trying to understand the geology of the region,” he said.