Researchers have discovered the fossilized remains of a tiny monkey that lived in Kenya about 4.2 million years ago. The monkey named Nanopithecus browni challenged scientists’ understanding of how primates evolved.

The prehistoric primate was the same size as the talapoin, the world’s smallest Old World monkey, which weighs only 2 to 3 pounds and is about the size of a pineapple.

The talapoins belong to a large group of monkey known as guenons, which can be found across Africa today and are usually larger than Nanopithecus browni.

Researchers thought that the evolution of the guenon are driven by changes in their forest habitats. The idea is that the species become bigger or smaller through the course of their evolution depending on the breakup and reconvergence of their ancient forest habitats.

Modern talapoins can only be found in West Central Africa and are confined to tropical forests. They are thought to have evolved to become smaller in response to a heavily wooded and swampy habitats.

Old World Monkeys
Modern talapoins can only be found in West Central Africa and are confined to tropical forests. The Nanopithecus browni was found in Kenya and lived in a dry habitat covered with open forests and grasslands. Carol Ward

The newly discovered fossil of Nanopithecus browni, however, suggests of more complex evolution of the guenon monkeys. It showed that the dwarfing of some guenon species occurred far longer than previously thought and may have occurred more than once. The evolution also likely occurred in very different habitats.

The Nanopithecus browni was found in Kenya on the eastern side of the continent at the Kanapoi habitat, which was dry and covered with open forests and grasslands. This habitat is far different from the tropical forest home of other guenon species in West Central Africa.

Interestingly, Kanopoo was also the site where the remains of some of the earliest humans, the Australopithecus anamensis, have been found. These human ancestors may have lived alongside Nanopithecus browni when both still existed.

"The discovery of Nanopithecus browni reaffirms Kenya's contribution to understanding the evolution and diversity of Pliocene fauna and the environmental contexts in which they lived," said Fredrick Kyalo Manthi, of the National Museums of Kenya. "Environmental changes during the Plio-Pleistocene may have influenced the present-day distribution of guenons."

The Nanopithecus browni was named after the late Francis Brown of the University of Utah, who made significant contributions to understanding the geological history of the Omo-Turkana Basin where the discovery site of the Nanopithecus browni is located.

The fossil of the Nanopithecus browni is now housed at the National Museums of Kenya. Researchers described the creature in a study published in the Journal of Human Evolution.