Calculus is tough stuff, as any dentist with their scraping tools can tell you.
Like bone, it lasts for ages.
"We can expect to find calculus even on very ancient samples," says Amanda Henry of the Max Planck Institute for Evolutionary Anthropology in Germany.
Henry studies glasslike particles, known as phytoliths, from plant eaten by homonins and sealed in their teeth tartar.
she has picked through calculus from the early hominin Australopithecus sediba, dating back 2 million years.