Tiger nuts (grass bulbs) were the staple diet of ancient ancestors, who inhabited East Africa between 2.4 million-1.4 million years ago, according to an Oxford University study. The hominins enriched their diet with fruits and invertebrates, like worms and grasshoppers.

The grass bulbs, which are rich in starches, are still eaten in many parts of the world today.

'Tiger nuts, still sold in health food shops as well as being widely used for grinding down and baking in many countries, would be relatively easy to find. They also provided a good source of nourishment for a medium-sized hominin with a large brain. This is why these hominins were able to survive for around one million years because they could successfully forage -- even through periods of climatic change," Dr Gabriele Macho, study author, said in a statement.

For the study, researchers determined eating habits of Paranthropus boisei (nicknamed 'Nutcracker Man' because of his big flat molar teeth and powerful jaws) by studying modern-day baboons in Amboseli National Park in Kenya. The baboons are believed to live in similar environments that the Nutcracker Men once lived in.

The researchers found that modern baboons consumed large amounts of tiger nuts, a C4 plant. The baboons displayed the same marks of wear and tear on the teeth which was a result of eating the nuts. Researchers said that these marks are formed because edible grass bulbs become extremely rough in an unheated state. Remains of Nutcracker man, such as tooth enamel, suggested that they were exposed to a harsh substance.

Tiger nuts were a large part of our ancestor's diet because it was easily available and has massive amounts of vitamins, fatty acids, and minerals. The nutritional content of tiger nuts is predicted to have played an important role in the growth of the hominin brain.

Previous studies showed that Nutcracker man majorly depended on diet rich in C4 plants like grasses and sedges. Critics have however debated if such high fiber foods were nutritious enough for the hominin's large brain.

The study has been published in the journal, PLOS ONE.