Pieter Camper was a fossil collector, and in 1786, he drew this jaw he’d acquired. He thought it belonged to a toothed whale. Another collector had a similar jaw from the same bunch of rocks (dug up near Maastricht), and *he* thought it was a crocodile.
Georges Cuvier (with Camper’s son) later proved that it was neither of those things, but an extinct marine reptile, Mosasaurus hoffmanni, who swam in the seas during those years when T. rex roamed around on land.
Luckily for us, Camper was Linda Hall Library’s Scientist of the Day a few days ago.