A recent scientific discovery had researchers buzzing about, of all things, tartar. That's right, the crusty deposits that the dentist scrapes off your teeth when you go for a cleaning. Except in this case, it was the tartar on the teeth of the nearly two-million-year-old Australopithecus sediba, which has been held up as a candidate ancestor for our genus, Homo. No one had ever before found tartar in an early hominin (a creature on the line leading to humans, after the split from the line leading to chimpanzees). And in analyzing the ancient tartar, the researchers had recovered evidence of what A. sediba ate. It wasn't at all what they expected.

In a paper published in July in Nature, Amanda Henry of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, Lee Berger of the University of the Witwatersrand in Johannesburg and their colleagues report on tartar, tooth chemistry and wear-mark analyses conducted on an adult female and a subadult male found at a site just outside Johannesburg. Their tooth chemistry indicated that over their lifetime they dined mostly on trees and shrubs (or, possibly, animals that ate those foods). This is surprising because other hominins of similar antiquity relied more heavily on tropical grasses and sedges.

The tartar analysis yielded traces of plant foods no one thought our ancient kin ate, such as bark. Berger notes that many primates use bark as a fallback food during times when fruit is hard to come by. He has speculated that the hominins, whose remains were recovered from what was once a deep underground cave, may have ended up there because drought conditions drove them to try to access a pool of water inside. The bark finding could bolster that scenario.

Conventional wisdom holds that Homo adapted to changing environmental conditions that favored the spread of grasslands by incorporating meat into its diet. A. sediba has small teeth, which are associated with an increase in higher-quality foods such as meat, and dexterous hands that may have been capable of making tools. So did A. sediba eat meat? With the “type of data we are getting, I think we will reach answers to these questions,” Berger says.

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