World's smallest fossil monkey found in Amazon

Scientists have uncovered remains of the smallest fossil monkey -- no heavier than a hamster - ever found in Peru's Amazon jungle. A team led by Duke University in the US and the National University of Piura in Peru found an 18-million-year-old fossilised tooth belonging to a new species of tiny monkey. The specimen is important because it helps bridge a 15-million-year gap in the fossil record for New World monkeys, according to research published in the Journal of Human Evolution.

The new fossil was unearthed from an exposed river bank along the Río Alto Madre de Dios in southeastern Peru. The researchers dug up chunks of sandstone and gravel, put them in bags, and hauled them away to be soaked in water and then strained through sieves to filter out the fossilised teeth, jaws, and bone fragments buried within. The team searched through some 2,000 pounds of sediment containing hundreds of fossils of rodents, bats and other animals before they spotted the lone monkey tooth.

"Primate fossils are as rare as hen's teeth," said Richard Kay, a professor of evolutionary anthropology at Duke. A single upper molar, the specimen was just "double the size of the head of a pin" and "could fall through a window screen," Kay said. Paleontologists can tell a lot from monkey teeth, particularly molars. Based on the tooth's relative size and shape, the researchers think the animal likely dined on energy-rich fruits and insects, and weighed in at less than half a pound - only slightly heavier than a baseball.

Some of South America's larger monkeys, such as howlers and muriquis, can grow to 50 times that heft. "It's by far the smallest fossil monkey that's ever been found worldwide," Kay said. The team dubbed the animal Parvimico materdei, or "tiny monkey from the Mother of God River." Now stored in the permanent collections at Peru's National University of Piura, the find is important because it's one of the few clues scientists have from a key missing chapter in monkey evolution. Monkeys are thought to have arrived in South America from Africa some 40 million years ago, quickly diversifying into the 150-plus New World species we know today, most of which inhabit the Amazon rainforest. Yet exactly how that process unfolded is a bit of a mystery, in large part because of a gap in the monkey fossil record between 13 and 31 million years ago with only a few fragments. "In that gap lies Parvimico.