Sinanthropus pekinensis replica

In 1941, with war raging in China, work on recovering unknown humanoid fossils in the highlands of China which began in 1934, came to a halt. The bones uncovered at Zhoukoudian ("Dragon Bone Hill") were unlike any seen before in the human family tree, and were named Peking Man. These remains (and nearly 200 others, never properly identified) were boxed at the request of the Chinese government, to be handed over to the United States for safe-keeping for the duration of the conflict. 

On December 3, 1941, the boxes were delivered by the Chinese army to an armed detachment of American Marines. From there, the box vanished into history. Though replicas were made of select fossils, the rest disappeared in the aftermath of the Japanese attack on Pearl Harbor. 

So then, what happened? It remains unclear. Perhaps the fossils were of those odd white apes discovered to be the secret of the lineage of the Jermyn family. Perhaps alien invaders from out of time destroyed them to cover up a monstrous secret. Perhaps the Karotechia or its predecessor intervened, interested in some fractured timeline of race or species the skulls spoke of. Perhaps remnants of P-Division stepped in, or the information was leaked to the British, and the box was interrupted by PISCES agents. 

In any case, this is a mystery that deserves investigation. 

More information at the Smithsonian.