Fossil Jaw Very Early Primate’s Mouse-Sized Animal Could Be Member Of Human Family Tree

Fossilized jaws from a mouse-sized animal that lived 40 million years ago may represent a new branch on the family tree of higher primates, including humans.

A fossil found in China has been identified as a virtually complete jaw of a primate that may have been an early ancestor of modern monkeys, apes and humans, according to scientists at the Carnegie Museum of Natural History in Pittsburgh, and the Institute of Vertebrate Paleontology & Paleoanthropology in Beijing.

A report on the discovery will be published Friday in the journal Science.

“This animal comes from very close to the point of diversification (in evolution) of the higher primates,” said Chris Beard of Carnegie. “This could be a model for the evolution of all the living higher primates.”

Beard said the new fossil represents a previously unknown species. It has been named Eosimias centennicus.

“We have found fossils for Eosimias before, but it was not as complete and it was from a different, but related species,” said Beard.

The find now proves that Asia, along with Africa, was home to some of the very earliest, prehuman primates, said Beard.

Walter Hartwig, a visiting professor of anthropology at George Washington University, said the importance of the find is “like saying I found the earliest remote ancestor of ourselves.”

Hartwig predicted, however, that Beard will be challenged “because previously he has suggested the same for other specimens from China.”

And, he added, “We are all keeping our fingers crossed that he finds skulls in addition to the teeth” because “teeth themselves are not the best possible evidence for identifying the fossil.”

John Fleagle, a professor of anatomy at State University of New York at Stony Brook, called Beard’s find “very impressive” because there has been relatively little evidence regarding anthropoids in Asia and because of the fossil’s age.

“This is really an exciting fossil and it vindicates pretty much everything he’s said so far,” Fleagle said. “But the ultimate, definitive proof will be finding a skull.”

Experts dated the fossil at about 40 million years, about 5 million years older than the widely-studied primitive primate fossils found in Egypt.

Eosimias centennicus is thought to have weighed about 3.5 ounces. The jaw details show many characteristics of higher primates, including a deep chin and dagger-like canine teeth, like those in many monkeys. Its blunt molars suggest the animal ate fruits and insects.

Higher primates included apes, monkeys and humans. The living lower primates include lemurs, tarsiers and bush babies. At some point in history, it is thought that the lower and higher primates shared a common ancestor and that the two branches separated on different evolutionary paths.

Higher primates are thought to have split away about 55 million years ago, early in what is known as the Cenozoic Era, or Age of Mammals.

Mammals are thought to have experienced most of their evolutionary diversity after the age of dinosaurs ended about 65 million years ago. Early mammals are thought to have been very small, with the primates and other species splitting into different branches over millions of years.

Science, which published the finding, is the journal of the American Association for the Advancement of Science.