Although there are many birds that cross entire oceans on their migrations, such “long-distance trips” are an absolute rarity among land mammals. But around 34 million years ago, a small African monkey species did just that: it crossed the then 1500 km wide Atlantic Ocean – presumably on a raft made of floating plant parts – and thus reached South America. Evidence of this fantastic journey comes from four teeth found in Peru from the descendants of these long-distance monkeys. This makes these primates the only third group of land mammals from which such an Atlantic crossing is known.
For a long time it was considered completely impossible for land animals to cross even larger seas on their way from one continent to another. At most an “island hopping” like in East Asia or during the Cretaceous period in Europe was thought conceivable – after all, there was numerous fossil evidence for this type of spread. However, as early as the 1980s, biologists came to the conclusion that at least two animal groups native to South America – the guinea pig-like (Caviomorpha) and the New World monkeys (Platyrrhini) – could not have migrated to the New World via the Bering Strait as previously assumed. Because their closest relatives were found exclusively in Africa and the Arabian Peninsula. “Both groups must have come from this region in the Eocene – which required one or more transatlantic crossings,” explains Erik Seiffert from the University of Southern California in Los Angeles and his colleagues.
African monkeys in Peru
But now the researchers have found fossil evidence that a third group of land mammals must have undertaken the dangerous journey across the Atlantic. The evidence for this is provided by four fossil teeth, some 23 to 34 million years old, which Seiffert and his team found on the banks of the Rio Yoruba on the border of Peru and Brazil. A closer analysis of the tooth characteristics showed that it was not a relic of a primeval New World monkey, but apparently a completely new type of primate. The paleontologists named it Ucayalipithecus perdita – Ucayali according to the area where it was found, pithecus is the ending used for primeval monkey species and perdita stands for “lost”. “The teeth of Ucayalipithecus are radically different from those of the Platyrrhini,” report Seiffert and his colleagues. Instead, the teeth were surprisingly similar to those of the Parapithecids, an extinct primate group that occurred in Egypt almost 50 to 25 million years ago.
But how did a member of these primeval monkeys known only from Africa come to South America? The paleontologists conclude from phylogenetic comparative analyzes that the immediate ancestors of Ucayalipithecus only separated from their African relatives around 35 million years ago. “This parapithecide provides us with the most convincing evidence of a phylogenetic connection between a fossil mammal from South America and an Afro-Arabian animal group,” say the researchers. Even though the location of the teeth today is far from the coast and around 4000 kilometers from the easternmost point of South America, the immediate ancestors of the Ucayalipithecus must have come directly from Africa to South America, they concluded.
On a raft of plant parts
But this means that the prehistoric monkeys must have crossed the Atlantic. “This is an absolutely unique discovery,” says Seiffert. “It shows that in addition to the new world monkeys and the guinea pig-like, this third lineage of mammals must somehow have made this incredible transatlantic journey.” The ancestors of the Ucayalipithecus would therefore only be the third group of mammals from which such a crossing of the Atlantic is known. On the basis of their data, the scientists suspect that the primates, about the size of a brush monkey, started this journey around 34 million years ago. At this time, at the transition from the Eocene to the Oligocene, the Antarctic ice sheet was just beginning to grow and sea levels were falling. As a result, the Atlantic, with a width of around 1,500 to 2,000 kilometers, was somewhat narrower than today – but still an enormous barrier for a land mammal.
The researchers suspect that the small prehistoric monkeys might have crossed the sea on a kind of raft made from plant parts. A storm might have torn the monkeys and the raft out to sea at that time. Favorable currents and winds could then have driven the involuntary seafarers to the coast of South America. The monkeys probably had to do without water and food for at least a few days. When they arrived in their new home, flexibility was again required: the newcomers were forced to get used to new food sources and a new environment. “This speaks for a high degree of flexibility in the behavior of these monkeys,” the scientists state.
Source: Erik Seiffert (University of Southern California, Los Angeles) et al., Science, doi: 10.1126 / science.aba1135