Piltdown Man, a fossil that supposedly proved early humans originated in England, was discovered in 1912, and wasn't proven a hoax until 1953. This fraud was one of the earliest fossil hoaxes out there — but it was actually two centuries too late to claim that distinction.
In the 1700s, two professors decided to humiliate their colleague by creating the silliest fossils ever dreamed up.
In the early 1700s, Johann Beringer was the Chair of Natural History at the University of Wurzburg, in what is now Germany. He was also the Chief Physician to the Prince Bishop. And he was also, in his colleagues Ignatz Roderick and Johann Von Eckhardt's opinion, a jerk who did not deserve the honors he'd received. Their rage was built up during debates about whether or not the strange fossilized bones that turned up on certain digs were evidence of an Earth ancient beyond comprehension, or whether they were simply the workings of God. Beringer was absolutely convinced that they were God's little doodles. Some say he was vocally contemptuous of anyone who opposed him. Some say his colleagues were cheating schemers. But all agree about what happened next.
Roderick and Eckhardt, skilled in carving limestone, arranged for certain things to turn up during Beringer's next dig. Sure enough, Beringer excitedly wrote about the 'fossils' of mating frogs, spiders in webs, and delicate insects he had discovered. The dig after that yielded actual writing, in Babylonian and Hebrew, carved into the rock. Beringer didn't catch on, even as the 'fossils' became more and more elaborate. Instead he published a book on the "capricious fabrications of God," and speculated as to why God had put them there. When the next dig turned up a fossil with his name on it, his credulity gave way to anger.
Some versions of the story say that Beringer was broken and disgraced — but historical data shows that it wasn't so. His ideas might have been old fashioned, but Beringer had a response to his tormenters that was truly suited to the modern world: he sued them. The hoaxers tried to bribe people into admitting responsibility for the fossils, but ended up getting caught themselves. They were disgraced. Beringer continued with his digs, turning up only legitimate fossils after that, and wrote several more books.
Via Archeology.org and Socy Berty.