Donald Prothero on Skepticblog gives a history of one of the exceptional finds in the history of North American paleoanthropology: "A tooth, a myth, and creationist lies".
When I visited the American Museum this fall to continue my research on fossil peccaries or javelinas (American pig-like creatures only distantly related to Old World pigs), I was keeping a close watch for one specimen in particular. Everyone who has fought in the evolution-creation wars has heard of it, and I wanted to finally see and touch the specimen for myself. It is the tooth that caused a sensation in the 1920s, and has since become something that creationists harp on excessively, even though their version of the story is full of lies and myths. It is the tooth known as Hesperopithecus haroldcooki (“Harold Cook’s western ape”).
It's a story that everybody should know, if they don't already. It was an honest, and understandable mistake that should not have gone as far as it did. It was not ridiculous to think that an anthropoid primate might be found in Nebraska in the Miocene -- after all, there is a long Eocene record of primates in Wyoming, and there are anthropoid primates today in the Americas. But Henry Fairfield Osborn went to press with the claim before other specialists had the opportunity to inspect and verify it.
The case is not alone in this quality -- a mistake goes to press and then other specialists shoot it down. That's what scientists do.