New Abu Dhabi Fossil Discovery Supports “Out of Africa” Monkey Dispersal

by AMNH on

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Just when and how Old World monkeys—a diverse and widespread group that includes macaques, baboons, and leaf monkeys—dispersed out of Africa and into Eurasia has never been fully understood. But a new discovery of an about 7-million-year-old monkey fossil from Abu Dhabi by a team of researchers at institutions around the world, including the American Museum of Natural History, provides important clues to the questions.

A closeup of the hand of a man in red and white turban holding a tiny fossil monkey tooth before the camera lens. It looks like a small stone with a notch in it.
The fossil monkey tooth just moments after discovery, in January 2009. 
©Brian Kraatz

“In addition to the ‘Out of Africa’ events associated with human evolution, we know that Old World monkeys also originated and migrated out of Africa millions of years ago, but until now, it has been unclear as to exactly when and how,” said Chris Gilbert, lead author of the study, published today in the Proceedings of the National Academy of Sciences, and a researcher at Hunter College-CUNY. “Relative to later events in human evolution, this is sort of like ‘Out of Africa: the Prequel.’”

It was previously thought that at least some of these monkeys, particularly macaques, may have dispersed into Eurasia over the Mediterranean Basin or Straits of Gibraltar around 6 million years ago, during a time period known as the Messinian Crisis. At this time, the Mediterranean Sea dried up, allowing animals to cross between North Africa and Europe.

The newly discovered fossil, however, indicates that Old World monkey dispersal could have taken place through the Arabian Peninsula even before the Messinian Crisis. The fossil, a very small lower molar, was discovered on Abu Dhabi’s Shuwaihat Island in 2009. 

Shuwaihat Island Expedition
The research team searching for tiny fossils at the monkey discovery site on Shuwaihat Island, United Arab Emirates, in January 2009. 
©Mark Beech

“When we found it, we were doing back-breaking sieving work searching for remains of tiny fossil rodents,” said Faysal Bibi, who was a Gerstner Scholar in the Museum’s Division of Vertebrate Zoology at the time of the work and is currently at Berlin’s Museum für Naturkunde. “We spent many days over consecutive years sieving through tons of sand at this one site. It paid off.”

CT Scans of the Fossil Monkey Tooth
CT scans of the fossil monkey tooth, which is just over half a centimeter long. 
©Christopher Gilbert

The team determined that this tooth belonged to the earliest known guenon, some of the most brightly colored and distinctive monkeys in modern African forests. The new specimen, dated to about 7 million years, pushes back the first appearance of the group by at least 2.5 million years. Previously, the oldest known guenon fossil was about 4 million years old. 

A close-up of a vervet monkey. The animal has light-colored body fur and a dark-skinned face with dark fur atop its head.
A vervet monkey, Chlorocebus pygerythrus, which is a common type of guenon found throughout sub-Saharan Africa.  
©Andrea Baden

And although they are found only on the African continent today, the new fossil suggests that, at one time, guenons extended their range outside of Africa. The discovery of a tree-dwelling guenon monkey in the Abu Dhabi desert also highlights the vast ecological changes that have taken place in the Arabian Peninsula, and future work in the area is critical to illuminate the evolutionary history of monkeys and other mammalian groups, the researchers say.

This work was supported in part by the Gerstner Scholars fellowship and the Gerstner Family Foundation.