While no dinosaur is exactly dime-a-dozen these days, one might argue that the hardest to find is the Archaeopteryx. And not just any old proto-bird, but specifically the one known as the “Maxberg specimen.” It was dug from a German quarry in 1956. Eduard Opitsch, the quarry owner, allowed the Maxberg Museum to display the specimen while he sought a buyer for his find. But, although he received bids from various museums, in the end he simply decided to keep it himself. He took the fossil home, and it was never seen again. When Opitsch passed away in 1991, his home and records were examined with no luck—the Archaeopteryx had flown the coop for good.