The "mystery human fossils" might even represent an entirely new species that existed alongside our own as recently as 11,500 years ago, according to a team of Chinese and Australian researchers.

Or the fossils might represent an especially early migration of so-called modern humans out of Africa and into East Asia, the team suggests.

Or—as some critical scientists have said—the evidence may tell us something we already know: People come in all shapes and sizes.

(Related: "New Type of Ancient Human Found—Descendants Live Today?")

"We have discovered a new population of prehistoric humans whose skulls are an unusual mosaic of primitive features, like those seen in our ancestors hundreds of thousands of years ago," evolutionary biologist Darren Curnoe of the University of