How And When Did Monkeys Get To South America?

Monkeys live today in the Old World (Africa and Asia) and in the New World (South America, Central America, and southern Mexico). The consensus has been that they originated in Africa, but it is not known with certainty how they managed to get to South America. You might think that the answer is they that they simply walked from Africa to South America, but the answer is not that straightforward. 

Here are the paleontologic facts: 

The earliest known fossils of monkeys are found in Africa (Egypt) and in South America (Bolivia and in the Amazon region of Peru). They are all about the same geologic age: latest Eocene/early Oligocene (about 33-35 million years ago). The problem is that there was 1,400 km of open ocean between Africa and South America at that time (and previously for a long time—millions of years earlier, during Cretaceous time).

So, that nagging question is: “how did monkeys get from Africa to South America.” The usual answer, which that has been around since the 1960s and is still in vogue today, is that African monkeys floated on clumps of forest vegetation (e.g., modestly large forested islets) that floated downriver and eventually ended up in the ocean. These clumps then drifted across the Atlantic Ocean to South America during late Eocene/early Oligocene time. The shortest distance would have would been 1,400 km, and the drifting is estimated to have taken at least 60 days. Then monkeys then would have had to transverse overland a long distance, from the eastern shores of South America, in order to reach the inland jungles of Bolivia. This widely believed “floating-vegetation theory” is commonly referred to as the “accidental transoceanic dispersal” theory. 

Another theory is that the earliest monkeys reached South America via southern North America during late Eocene time. This theory, as well as the one discussed above, are questionably indicated on the following known paleogeographic map that shows the position of South America, relative to North America and Africa during the late Eocene. The few scientists who advocate this second theory of a dispersal route via North America have proposed, furthermore, that monkeys originated even earlier that late Eocene time. For example, in Wyoming, a sparse record of early Eocene fossils that resemble marmosets (= New World monkeys) is known.

 

While you contemplate the unsolved mystery of the ancient geographic dispersal of monkeys, it is useful to give you some background biologic information to consider. Monkey are primates. Primates include the prosmians (lemurs, bush babies, lories, pottos, and tarsiers) and also the anthropoids (monkeys, gibbons, apes, and humans). Old World monkeys consist of several families, and these are referred to as the catarrhines. They are characterized by having nostrils separated by only a thin partition, and they also have jaws with two premolars. Two examples of catarrhines are the macque monkey and baboons. Old World monkeys do not have prehensile tails. Old World monkeys include both arboreal (live in trees) and ground-dwellers.

An example of a modern-day catarrhine monkey (from Japan) is shown above. Photo credit: Wikipedia, 2021.

The New World (South America, Central America, and southern Mexico) monkeys are referred to as the platyrrhines. They are characterized by having nostrils that are quite separate, and they also have jaws with three premolars. Two examples of platyrrhines are shown here: cebids and marmussets New World monkeys have a grasping prehensile tails. New World monkeys are only arboreal.

An example of a modern-day platyrrhine monkey (cebid) from Costa Rica. Photo credit: Wikipedia, 2021.

A second example of another modern-day platyrrhine monkey (marmoset). Photo credit: Wikipedia, 2021.

A relatively recently published comparative study of mitochondrial genes of primates has been interpreted as agreeing with the fossil data showing that platyrrhines split from catarrhines at around 35 million years ago. The authors of the mitochrondrial study also advocated the “floating on vegetation” theory (see discussion above).

USEFUL REFERENCE;

For an excellent article concerning evolution of mammals in South America, I highly recommend: https://dcpaleo.org/south-americna-fossil-mammals/