So, they used teeth found near a site full of discarded sea shells, did all sorts of fancy acid dunking to get crud off of the teeth and in the end they found out that the teeth owners ate shell fish. That is simply amazing analysis.
Weirdly enough, another team of researchers studied the shells, and found out the mussels had a steady diet of human teeth, but it didn't make the papers due to a gov't conspiracy to suppress the truth. ;')