Piltdown Man is the most famous scientific fraud of the last hundred years.
In 1912, it was announced that the skull and jaw of a pre-human had been found in Britain. Similar fragments were found nearby in 1913 and 1915, by the same people.
In 1953, chemical tests proved that the fossils were frauds. Someone had taken a slightly odd "modern" human skull, and the jaw of an orangutan. They had been stained, filed, smashed, and so on, in a fairly clever way.
The fraud led a charmed life. A few prominent British scientists failed to perform tests that they really should have done. And, they more or less kept others away from the fossils. Some historians go so far as to believe that these men were co-conspirators. Or, maybe they just blew it.
At first, fraud wasn't even suspected. The fossils were, after all, cleverly done, and no money was involved. There were other European finds - Neandertal, Cro-Magnon, and Heidelberg - so another European "missing link" wasn't too surprising.
After the first publication, many scientists commented that the jaw seemed to be from a chimpanzee. They expressed strong doubt that the skull and the jaw were from the same species. The hoaxer(s) solved this by planting a second jaw and second skull at a second location. After that find, some of the doubters were satisfied.
Piltdown man used to be used as evidence that early Man developed intelligence before developing in certain other ways. More recent discoveries, such as Lucy, have pretty well trashed that argument.
Parker, Gary E., "Origin of Mankind," Impact No. 101, Creation-Life Publishers, 1981 p.4Searches through Piltdown bibliographies haven't turned up even one single dissertation. So, 500 of them is just completely impossible. The number 500 does turn up in an editorial written shortly after the hoax was exposed:
More than five hundred articles and memoirs are said to have been written about Piltdown man.The most plausible explanation is that Parker heard this quote, and somehow turned "articles and memoirs" into "dissertations". Parker is not a careful scholar.
Nature vol. 274, #4419 (10 July 1954) pp. 61-62