New World Monkey Family Tree Reconstructed

When monkeys landed in South America about 37 million years ago, the long-isolated continent teemed with 30-foot snakes, giant armadillos and strange, hoofed mammals. Over time, though, these monkeys forged their own niches across the New World as they evolved and spread. Now, scientists have applied decades' worth of data in order to reconstruct the New World monkey family tree.

Today, more than 150 species of monkeys inhabit the New World, ranging in size from the pygmy marmoset to the muriqui--a long-limbed monkey that tips the scales at 25 pounds. Researchers know from molecular studies that monkeys have their closest relatives in Africa and Asia, but that doesn't quite explain how they got to South America in the first place.

South America split from Africa long before monkeys evolved. In addition, the scarcity of monkey ancestors in the North American fossil record makes a southward migration highly unlikely. In order to learn a bit more about the past of these monkeys, the researchers sequenced the DNA of living monkeys. This allowed them to come to a clear consensus of how the different species and genera are related.

The scientists studied the minute differences in shape, size and structure in fossilized bones. In all, they examined 399 different features of teeth, skulls and skeletons from 16 living and 20 extinct monkey species from South America and Africa. Then, using software that reconstructs evolutionary relationships, the scientists created a family tree. The researchers compared this tree to a second tree, built strictly from the molecular studies of living species, in order to see if the two types of studies affirmed or contradicted one another. Except for a few cases, the trees looked remarkably similar, which validated conclusions based on the anatomy of fossils.

"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," said Richard Kay, one of the researchers, in a news release. "So if you want to learn about what was going on in the Amazon, you have to look at its periphery."

That's not all the scientists learned, either. They also looked at long-term changes in South America's climate. This allowed them to make sense of the evolutionary pattern revealed by the monkey fossils.

The findings reveal why lineages that evolved outside the Amazon Basin were evolutionary dead ends. For example, when the climate in Patagonia turned cool and arid, the primates there went extinct. In addition, monkeys of the Caribbean islands became extinct as the result of the appearance of humans and/or sea level rise. The research reveals a bit more about these New World monkeys and their evolutionary history.

The findings are published in the journal Molecular Phylogenetics and Evolution.