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Early Human Ancestor Did Not Have Jaw, Tooth Structure Fit For Hard Food Diet

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We enjoy munching on some types of food because it's easy to bite on them, but for a potential evolutionary ancestor, it probably wouldn't be.

The Australopithecus sediba -- a small, ape-like species whose fossils were discovered in 2008 -- would have had a difficult time gnawing a hard food diet. Doing so would easily dislocate their jaw.

A study in 2012 had suggested that the A. sediba had lived on a diverse woodland diet consisting of hard food mixed in with tree bark, fruit, leaves and other plant products.

But a new research featured in the journal Nature Communications revealed that the hominid didn't have the nutcracker jaw and teeth structure necessary to exist on a steady hard food diet.

An Important Limitation

Anthropology Professor David Strait, the lead researcher of the new study, said most australopiths had remarkable adaptations in their jaws, teeth and faces that allowed them to eat types of food that were difficult to crack open or chew. These species were able to efficiently gnaw food with strong forces.

However, Dr. Justin Ledogar, co-researcher of the study, said the A. sediba's chewing prowess was very limited.

"If it had bitten as hard as possible on its molar teeth using the full force of its chewing muscles, it would have dislocated its jaw," said Ledogar.

Strait and his team studied the A. sediba fossil skull unearthed in 2008 from the Malapa cave near Johannesburg, South Africa.

The biomechanical techniques used in the study were similar to those applied by engineers to test whether cars, planes, machine parts or other mechanical devices were strong enough to avoid breaking.

A Backwards Evolution

The A. sediba has been thought to lie near the ancestry of Homo, the group in which our species belong. The new findings support the assertion that A. sediba was a midway species between A. africanus and either H. habilis or the later H. erectus, albeit not directly.

Ledogar said humans also have the biting limitation. He and his colleagues suspect that early Homo species also had the limitation, but other australopiths they studied were not as limited in this regard.

This indicates that while some australopith populations were evolving to maximize their ability to bite powerfully, others such as the A. sediba were evolving in the reverse direction.

Some of these species who evolved in the opposite direction ultimately gave rise to Homo, researchers said.

A vital way to understanding the origin of our genus would be to realize that ecological factors may have disrupted the diets and feeding behavior of australopiths.

"Diet is likely to have played a key role in the origin of Homo," said Prof. Strait.

The bottom-line: the early hominids may have eaten hard food, but they weren't adapted to do so. They also were more likely to rely on food that was easier to chew.

 The Australopithecus sediba

The A. sediba was a small pre-human species that roamed the Earth about 2 million years ago. They appear in the fossil record about four million years ago.

Although australopiths had human traits such as being able to walk upright on two legs, many of them lacked human features such as a large brain, advanced tool-use, and flat faces with small jaws and teeth.

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