New World Monkey Evolution And Migration
January 4, 2014

Study Examines Evolution, Migration Of Primates In The Americas

redOrbit Staff & Wire Reports - Your Universe Online

After landing in South America approximately 37 million years ago, primates spread as far north as the Caribbean and as far south as Patagonia, according to research currently appearing online in the journal Molecular Phylogenetics and Evolution.

During their travels, they also evolved new forms and carved out their own niches in the New World, according to the study authors. Today, more than 150 different species of monkey live in the region, ranging in size from the tiny pygmy marmoset to the 25-pound long-limbed muriqui.

“We know from molecular studies that the monkeys have their closest relatives in Africa and Asia -- but that doesn't explain how they got to South America, just that they did,” explained Duke University evolutionary anthropologist Richard Kay. Kay and his colleagues analyzed several decades’ worth of geological, climatic and other data to discover several patterns in the creatures’ migration and evolution upon their arrival in the Americas.

Monkeys evolved well after the continents of South America and Africa split, and the lack of monkey ancestors in the North American fossil record makes it unlikely that primates migrated towards the south. That has caused scientists to speculate that the creatures crossed the Atlantic Ocean on some sort of vegetation raft, either propelled by a powerful storm or traveling more deliberately using islands that have since sunk into the ocean.

The first fossil evidence of monkeys in the Americas came roughly 11 million years after they first arrived, meaning that there are few details of their evolution during that period. The humid and heavily-forested landscape of what is now the Amazon Basin made fossil formation difficult and modern exploration and recovery efforts equally as hard. However, the events that took place there are essential to New World monkey evolution, the authors said.

“However they got to South America, they were evolving in the Amazon Basin, and from time to time they managed to get out of the basin. So if you want to learn about what was going on in the Amazon, you have to look at its periphery,” Kay said, adding that such research can be conducted in areas like Chile and Patagonian Argentina.

The Amazon Basin has been warm and wet for many years, helping make it a reservoir of primate biodiversity, the researchers explained. When weather and sea level conditions were right, the monkeys spread to other regions such as Patagonia, the Caribbean islands, and Central America. New species emerged in those locations, where conditions were more favorable for fossil preservation and from which Kay obtained the fossils he studied.

In the absence of DNA evidence of ancient primate species, the investigative team examined various fossilized bones. They reviewed 399 different features of teeth, skulls and skeletons from 16 living and 20 extinct monkey species from South America and Africa, then used computer software to reconstruct evolutionary relationships.

Kay then took the resulting family tree and compared it to a second, built solely from molecular studies of living monkey species, in order to see if they squared with each other. With a few minor exceptions, the two primate family trees were said to be remarkably similar in appearance.

Furthermore, by analyzing long-term changes in South America’s climate, geological features and sea level, the professor was able to determine when and how monkeys reached the Caribbean islands and the far southern end of South America – thousands of miles south of where they now currently live. In his study, Kay suggests that the animals originated from South America, not Central America, and like their ancestors floated there by chance.

Image 2 (below): This diagram shows the relationships among monkey groups that currently inhabit South and Central America. Credit: Richard Kay