Fossil find adds three million years to oldest known old-world monkey

(Phys.org) —Researchers from the United States have identified fossilized remains found in Kenya seven years ago, as those belonging to an old-world monkey (Cercopithecidae) and relative of modern proboscis and colobus monkeys—they date back to a time 3 million years before any other previous find of its kind. In their paper published in Proceedings of the National Academy of Sciences, the team describes the fossils as two teeth—a molar and a premolar—enough to identify its owner as a member of a group of old-world monkeys of the Cercopithecoidea superfamily.

Old-world monkeys are a group of primates that include monkeys that evolved in Africa and Asia (as opposed to new-world monkeys that evolved in the Americas, etc.) One of their distinguishing features is that unlike new-world monkeys, their tails are not prehensile. They are believed to have emerged as a group during the Miocene epoch, a period that lasted from 5 to 23 million years ago. The newly identified fossils have been found to be approximately 12.5 million years old and were found in 2006 at a site in Tugen Hills, Kenya. The researchers believe that at the time the monkey was alive, the place where it lived was grassland.

The researchers have identified the fossilized teeth as coming from one or two colobine monkeys—their modern counterparts include proboscis (known for their large oddly shaped nose) and the colobus, which actually looks similar to a skunk. They believe the monkey weighed about ten pounds and based on the look of the teeth, ate mostly seeds and perhaps unripe fruit, rather than leaves—the main component of the diet of modern similar monkeys. This suggests, they say, that the evolution of a more advanced gut was underway that would lead to an ability to digest leaves. It also offers clues that might hint at the competition that likely existed between the colobine monkeys and other archaic primates, which subsequently resulted in some of those other species going extinct.

The identification of the fossils is helping to answer some of the questions scientists have about the origin of old-world monkeys and how they diversified as so few of their fossilized remains have been found.

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