In the badlands of Wyoming, scientists have discovered a handful of fossils that show the earliest evidence of a physical difference between male and female primates that suggests the males kept harems of females 50 million years ago.

The find includes the remnants of three lower jaws, one snout and three maxillary bones from the species Notharctus venticolus, a cat-sized animal that lived in trees and ate fruit and insects. Two of the jaws and one of the maxillary bones had canine, or fang, teeth half the length of those in the other specimens. Scientists say the longer canines probably belonged to males and the shorter teeth belonged to females.

The difference in tooth length indicates that males competed fiercely for females, the scientists say. They base this belief on the behavior of some baboons and South American monkeys, which have a similar variation in canine size and which keep female harems.

"If the difference in canine size reflects the same kind of behavior patterns of living monkeys and apes, it is possible that among these 50 million-year-old primates, the males competed aggressively for females and may have kept harems -- harems in the sense that one male would mate with and protect several females over time," said Leonard Krishtalka, curator of vertebrate paleontology at Pittsburgh's Carnegie Museum and one of the scientists who discovered the fossils.

The find is described in the July 2 issue of the Proceedings of the National Academy of Sciences.