Crew of prehistoric monkeys rafted across the Atlantic to South America

Paleontologists crossing the Rio Yurúa in Amazonian Perú, with the Santa Rosa fossil site in the background. [Credit: Dorien de Vries]

A crew of now-extinct monkeys made a treacherous transatlantic journey on a natural raft from Africa to settle in South America around 35 million years ago, according to a study of fossilized teeth found in Perú.

It’s believed the prehistoric Ucayalipithecus monkeys made the more than 900-mile trip across the Atlantic (a narrower ocean at the time) on floating islands of vegetation that broke off from coastlines, possibly during a tropical storm.
“It would have been extremely difficult, though very small animals the size of Ucayalipithecus would be at an advantage over larger mammals in such a situation, because they would have needed less of the food and water that their raft of vegetation could have provided,” said lead author Erik Seiffert, a professor of clinical integrative anatomical sciences at Keck School of Medicine, University of Southern California. The study was recently published in the journal Science.
“This is presumably why most of these overwater dispersal events that we know of in the fossil record involve very small animals,” Seiffert said.

Only two other species of “immigrant” mammals are thought to have made what would have been a harsh crossing across the Atlantic, although exactly how they got there has long been a topic of heated discussion.

One was New World Monkeys, or platyrrhine primates, which are five families of flat-nosed primates that are found in south and central America today. The other was a type of rodent known as caviomorphs, ancestors of creatures like the capybara.

Erik Seiffert inspecting a tiny fossil at the Santa Rosa site in Amazonian Perú. [Credit: Dorien de Vries]

Erik Seiffert inspecting a tiny fossil at the Santa Rosa site in Amazonian Perú. [Credit: Dorien de Vries]

Teeth like ‘fingerprint for paleontologists’

The team of researchers found the molars during an excavation of the left bank of the Yuruá River in the Peruvian Amazon. The animal has been named Ucayalipithecus perdita, which comes from Ucayali, the area of the Peruvian Amazon where the teeth were found, pithikos, the Greek word for monkey and perdita, the Latin word for lost.
It would have weighed about 12 ounces (350 grams) and was similar in size to some marmosets that live in South America today.
Seiffert said that the fossilized molars strongly resembled those of a now-extinct family of African primates called Parapithecidae, who lived in what is now Egypt, Libya, and Tanzania some 23 million to 56 million years ago.
“If Ucayalipithecus was like its African parapithecid relatives, it would have lived in the trees and probably would have been an agile leaper,” Seiffert said.
Mammals teeth, and particularly the molar teeth, are extremely diverse in shape, and the unique arrangements of bumps and crests on teeth are almost like fingerprints for paleontologists, Seiffert explained.

Tiny molar teeth of Ucayalipithecus perdita from the Santa Rosa fossil site in Amazonian Perú.

Tiny molar teeth of Ucayalipithecus perdita from the Santa Rosa fossil site in Amazonian Perú.
“The teeth of Ucayalipithecus allow us to place this monkey in the primate family tree, but also tell us something about what it ate – in this case, it would appear that Ucayalipithecus probably ate primarily fruit.”

Improbable find

Seiffert said that he had been skeptical that animals could have “rafted” across an ocean but he said a video of pieces of land floating down the Panama Canal after a storm had helped convince him. He said that natural rafts could have sustained upright trees that might have borne fruit.

“If a small primate caught a ride on a raft like this, it seems very plausible that they could make it such a long distance,” he said.

Seiffert said the site where the fossils were found was along a riverbank in a remote part of the Peruvian Amazon, where there are no roads and everything has to be flown out in a small plane.
“The thing that strikes me about this study more than any other I’ve been involved in is just how improbable all of it is,” said Seiffert.
“The fact that it’s this remote site in the middle of nowhere, that the chances of finding these pieces is extremely small, to the fact that we’re revealing this very improbable journey that was made by these early monkeys, it’s all quite remarkable.”

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