Scientists last week announced they had unearthed a 50 million-year-old skull of a bug-eyed, jug-eared primate, a creature no bigger than a mouse, but a find that upsets the traditional family tree that includes monkeys, apes and humans.

A team from the Carnegie Museum and the Denver Museum of Natural History uncovered four skulls of a primitive version of a tiny primate called a tarsier that lived in Wyoming when the cowboy state was covered with a lush palm-studded forest.

The creature had goggle eyes, a very short muzzle and enlarged bony ear chambers. It ate bugs and fruit. Modern tarsiers are nocturnal tree dwellers in the tropical forests of Southeast Asia.

What makes the fossilized remains of the tarsier interesting is their age. Until now, the evolutionary tree had tarsiers and anthropoids, which include the ancestors of monkeys and man, splitting apart 35 million years ago. Apparently, that is incorrect. The tarsiers went their own way at least 50 million years ago, while the earliest known anthropoid is from Africa and only 35 million years old.

"This means that the fossil record of at least the first 15 million years of anthropoid evolution is missing and awaits discovery," the scientists said. Their report appeared in the Jan. 3 issue of Nature.