Bits of food stuck between the teeth of a two-million-year-old South African hominid show that, unlike almost all other known human ancestors, it ate tree bark and other hard foods.
Australopithecus sediba's diet was dramatically different to that of its African cousins, which tended to eat grasses and sedges.
A sediba's diet was analyzed using a technique that involved zapping fossilized teeth with a laser to free carbon from their enamel. This allowed the scientists to pinpoint the types of plants that were consumed and the environments in which the hominids lived.
The carbon signals from the teeth are split into two groups: C3 plants like trees, shrubs and bushes, and C4 plants such as the grasses and sedges consumed by many other early hominids.
And the teeth from the two A sediba individuals analyzed in the study delivered carbon isotope values outside the range of all 81 previously tested hominids. "The lack of any C4 evidence, and the evidence for the consumption of hard objects, are what make the inferred diet of these individuals compelling," said Sandberg.
"It is an important finding, because diet is one of the fundamental aspects of an animal, one that drives its behavior and ecological niche," says CU-Boulder doctoral student Paul Sandberg.
"As environments change over time because of shifting climates, animals are generally forced to either move or to adapt to their new surroundings."
The bark may represent a seasonal element to A sediba's diet. Bark and woody tissues haven't previously been found to be a dietary component of any other ancient African hominids, but are eaten by many primates and contain both protein and soluble sugars. The diet of A sediba may have been similar to that of today's African savanna chimpanzees, says Sandberg.
A sediba, first discovered in 2008, appears to have characteristics of both primitive and modern hominids, including a human-like ankle, short fingers and a long thumb - and a relatively complex brain. It's still unclear exactly where they fit in the hominid family tree.