In pretoothbrush populations, a thick, visible crust of calcium phosphate, food particles, and trapped microorganisms often marred gumlines. Dental calculus, or tartar, still plagues many, and dentists attack it with metal picks and abrasives. "It's a meandering line of caramel-colored, cementlike material," says Christina Warinner, an anthropologist at the University of Oklahoma, Norman. "It's quite gross." It can also be a treasure for those studying ancient DNA. At a recent meeting here,* researchers noted that the microbial DNA preserved in ancient dental calculus-and in equally prosaic human coprolites (fossilized or preserved feces)-carries a record of the communities of bacteria that lived in and on people who died hundreds or thousands of years ago. "I think it's the biggest untapped resource in ancient DNA," says Laura Weyrich, a microbiologist at the University of Adelaide in Australia, who co-authored a paper on DNA in calculus from fossilized teeth earlier this year (Science, 22 February, p. 896). "We've just scratched the surface."
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