Unearthed in China, the mouse-sized creature has a mix of anatomical features that make it quite unlike any other primate—living or extinct—known to science. The discovery was published Wednesday in the journal Nature.
By about 55 million years ago, the earliest primate ancestors of humans had split into two branches. One branch gave rise to lemurs, lorises and bush babies. The other led to tarsiers, whose enormous-eyed, tree-dwelling descendants still live in Southeast Asia. The second branch also gave rise to anthropoids, including monkeys, apes and humans.
The animal described in the study is a primitive tarsier relative. It is of interest to scientists because it lived at a crucial period, fairly soon after the two branches split.
The discovery gives new insight into very early ancestors of humans: How big they were, what they looked like, what their anatomy was like, what they ate and how they moved.
For example, many scientists believed that the specialized anatomy of a monkey's foot developed much later. But some of that anatomy can be seen in the unearthed skeleton—far, far earlier in evolution.
"It has a monkey-like foot but a body more or less like a tarsier's," said Daniel Gebo, co-author of the paper and anthropologist at Northern Illinois University. "It's the first time we've seen this combination."
The finding also is striking because of the completeness of the skeleton. Until now, scientists only had seen fragmentary remains of these ancient primates, such as teeth, jaws or skulls.
"It's rare because most of the important parts of this skeleton are there," said Jerry Hooker, a paleontologist at London's Natural History Museum, who wasn't involved in the study. "It's only lacking hands and wrists, which is a pity."