Tracking our Extended Family

Chris Beard

Two exciting fossil discoveries offer clues to the origin and evolution of higher primates—the group that today includes monkeys, apes, and humans. Carnegie Museum of Natural History Curator of Vertebrate Paleontology Chris Beard, PhD, and associates are helping us understand who we are and where we came from.

A team of American and Chinese paleontologists, organized by Beard, unearthed foot bones of Eosimias, an early primate that lived about 40–45 million years ago in China. These bones provide us with our first glimpse at the skeleton of primates that are near the common ancestry of monkeys, apes, and humans.

Beard and his team of researchers also discovered the fossils of the world's smallest known primates. Approximately the size of a human thumb, these creatures once roamed ancient rainforests near the eastern coast of China. These long-extinct primates are also surprisingly close relatives of monkeys, apes, and humans.

The first skeletal remains of Eosimias
T he fossilized foot bones of Eosimias, an early higher primate that lived 45 million years ago, present the first unambiguous evidence that bridges the anatomical gap between lower primates such as lemurs and tarsiers, and higher primates such as monkeys, apes, and humans.

Eosimias Illustration: Nancy Perkins

Previously, paleontologists had found only jaws and teeth of Eosimias, a primitive tree-dwelling primate about the size of the smallest living monkeys. Because of the lack of available skeletal evidence, paleoanthropologists had been divided as to exactly where Eosimias fit on the primate family tree. Some scientists even doubted that it was a primate at all.

Beard, a leader of the joint American–Chinese expedition that resulted in the discovery, says the discovery is important because it fills a gap in the fossil record of humans and their nearest relatives.

The smallest known primate species
Beard's team of American and Chinese scientists also discovered the fossils of the world's smallest known primate species. Many of the fossils are one-third the size of Madagascar's mouse lemur, which at one ounce is the smallest living primate. These fossils may help scientists understand further the evolutionary family tree of primates, a group characterized by larger brains, grasping hands and feet, nails instead of claws, and eyes located in the front of the skull.

The tiny fossil primates also belong to a branch of primate evolution that eventually leads to humans. This surprising discovery shows that the earliest common ancestors of monkeys, apes, and humans were smaller than any living primate, and would have been the size of a living shrew. The tiny creatures were most likely tree dwellers that relied on a steady diet of insects and nectar. They were probably nocturnal, solitary creatures.

For more information

• Press Release: Eosimias
• Press Release: Primate evolution
• Chris Beard
• Link to audio of Beard's All Things Considered interview