Here you will find a cast of the Piltdown specimen. Both the skull and mandible were real bone; the problem is that the skull was human and the jaw orangutan. The remains were interred in a gravel bed where they were later unearthed and reconstructed. What you see here is the reconstruction. The darkened parts are the real bone, the lighter parts sculpted from plaster.
The scientists who interpreted the Piltdown specimen believed it to be Early Pleistocene in age, making it possibly the earliest fossil human relative known at that time. They debated whether it could be linked to Pithecanthropus, now known as Homo erectus, and whether it was older or younger. Only later was it shown definitively that the specimen combined two different modern species, and that the scientists had been duped.
What to do: Obviously, if Piltdown had not been a fake, it would predict a very different pattern of evolution from the one we now understand to explain the fossil record. Think about aspects of the present fossil record that are inconsistent with the Piltdown specimen. You can choose any part of the real fossil record for your examples, but be specific about the evolutionary changes that happened at the wrong time to be consistent with Piltdown.
Hint: look at the browridge.