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鈥淲E ARE, effectively, looking back 2 million years and watching our ancestors chew their food,鈥� says . A palaeontologist at the University of the Witwatersrand in Johannesburg, South Africa, he shot to scientific stardom in 2010 when he discovered Australopithecus sediba, one of the most remarkable fossils of the hominin lineage known to date.

Now he, Amanda Henry of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and a team of collaborators have discovered what A. sediba ate. Main course: bark.

A. sediba is known from two skeletons uncovered in South Africa. The species shares a mix of features seen in earlier australopithecines, modern humans and chimpanzees. They also had poor dental hygiene. From plaque on the fossils鈥� teeth, the team extracted traces of A. sediba鈥檚 food. They found signs of fruit, bark and woody tissues (Nature, ).

鈥淭hat blew me away,鈥� says Berger. 鈥淚 had never heard bark associated with what we ate before.鈥�

Primatologists were less surprised. Many primates chew on bark when times are tough. Greater dietary surprises were in store though. The team looked at the carbon isotopes in A. sediba teeth to see what types of plants they ate. A 鈥淐₄鈥� signature is typical of savannah plants like grasses and the grain they carry. These plants fix carbon in a four-carbon molecule. 鈥淐₃鈥� indicates fruits and leaves foraged from a more forested environment.

The team expected a C₄ signature 鈥� it鈥檚 what most hominins have and fits the environment that A. sediba lived in. They found the exact opposite. A. sediba, concludes Berger, was a picky eater. Why is still a mystery, but for Berger, picky eaters are clever: 鈥淭hey had to be smart enough to select specific foods from their environment.鈥�