The story of how monkeys conquered the world is a remarkable tale that includes an improbable trip across the Atlantic on a floating island that broke away from mainland Africa. In yet another twist, researchers have just uncovered the remains of an ancient species that lived in what is now China some 6.4 million years ago, suggesting that monkeys had reached the Far East at a time when ancient apes still roamed Asia.
"This is significant because they are some of the very oldest fossils of monkeys outside of Africa," explained Nina Jablonski from Pennsylvania State University. "It is close to or actually the ancestor of many of the living monkeys of East Asia. One of the interesting things from the perspective of paleontology is that this monkey occurs at the same place and same time as ancient apes in Asia."
Reporting in the Journal of Human Evolution, Jablonski and colleagues explain that the fossils date back to the Miocene, a period in which monkeys rarely came into contact with apes in Eurasia as changing environmental conditions led to the extinction of many ape species.
Prior to this discovery, the only known co-occurrence of the two types of primate occurred at Maragheh in Iran, where monkey and ape fossils were found in the same layer of sediment dating back 7.6 million years.
The new discovery at the Shuitangba lignite mine in Yunnan province includes the jaw bone and femur of a single individual, as well as a calcaneus – or heel bone – slightly deeper in the sediment. Based on the dental morphology present, the researchers believe that the monkey belonged to the ancient species Mesopithecus pentelicus, which was first discovered in the early 19th century at a site near Athens, Greece.
"These monkeys are the same as those found in Greece during the same time period… suggesting they spread out from a center somewhere in central Europe and they did it fairly quickly,” explained Jablonski. “That is impressive when you think of how long it takes for an animal to disperse tens of thousands of kilometers through forest and woodlands."
The secret to the species’ rapid spread across the globe is partially explained by the nature of its femur and heel bone, both of which suggest that it was a very agile creature that was as comfortable leaping through the trees as it was walking on land. As such, it would have been highly adaptable, and would have been able to cross both forest and open country on its journey eastwards.
On top of this locomotive versatility, M. pentelicus also benefited from what the study authors describe as “dietary flexibility,” whereby it was able to survive on a range of hard-to-digest and nutrient-poor food. This is because, like other Old World monkeys – or colobines, as they are otherwise known – M. pentelicus possessed stomach enzymes that allowed it to ferment cellulose, much like modern cows.
As a result, it was able to survive on leaves, nuts, and seeds, as well as fruit and other plants, obtaining nutrients from the fatty acids that were made available by bacteria during the fermentation process. This ability to switch up its diet would have allowed M. pentelicus to navigate alterations in seasonal conditions and more widespread climate change, all of which facilitated its passage across Eurasia.
This incredible adaptability has since been passed on to numerous modern species of colobine that can be found throughout Asia, many of which live in some of the most seasonally extreme habitats occupied by non-human primates.