Australopithecus sediba, a diminutive pre-human species that lived about two million years ago in southern Africa, has been heralded as a possible ancestor or close relative of Homo. (Photo: Pixabay)

Washington: A possible early human ancestor did not have the jaw and tooth structure necessary to exist on a steady diet of hard foods, a new study has found, suggesting that dietary changes were shaping the evolutionary paths of

early humans.

Australopithecus sediba, a diminutive pre-human species that lived about two million years ago in southern Africa, has been heralded as a possible ancestor or close relative of Homo.

Australopiths appeared in the fossil record about four million years ago, and although they have some human traits like the ability to walk upright on two legs, most of them lack other characteristically human features like a large brain, flat faces with small jaws and teeth, and advanced tool-use.

"Most australopiths had amazing adaptations in their jaws, teeth and faces that allowed them to process foods that were difficult to chew or crack open," said David Strait from Washington University in St Louis.

"Among other things, they were able to efficiently bite down on foods with very high forces," said Strait. "Australopithecus sediba is thought by some researchers to lie near the ancestry of Homo, the group to which our species belongs," said Justin Ledogar from the University of New England in Australia.

"We find that A sediba had an important limitation on its ability to bite powerfully; 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," he said. The study describes biomechanical testing of a computer-based model of an Australopithecus sediba skull.

The model is based on a fossil skull recovered in 2008 from Malapa, a cave near Johannesburg in South Africa. Though the study does not directly address whether Australopithecus sediba is indeed a close evolutionary relative of early Homo, it provides further evidence that dietary changes were shaping the evolutionary paths of early humans, they said.

"Humans also have this limitation on biting forcefully and we suspect that early Homo had it as well, yet the other australopiths that we have examined are not nearly as limited in this regard," said Ledogar.

"This means that whereas some australopith populations were evolving adaptations to maximise their ability to bite powerfully, others (including A sediba) were evolving in the opposite direction," Ledogar said. "Some of these ultimately gave rise to Homo. Thus, a key to understanding the origin of our genus is to realise that ecological factors must have disrupted the feeding behaviours and diets of australopiths," he added.

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

The findings were published in the journal Nature Communications.