Washington (AFP) - A three-million-year-old child's skull uncovered in South Africa has no signs of the kind of soft spot that would be seen in human children with larger brains, a study said Monday.
The findings are the latest contribution to long-running debate over whether the Taung Child fossil may have represented the earliest signs of a fusing skull.
Babies today are born with a number of plates in their skull that are loosely joined, forming soft spots that eventually come together.
Scientists believe we evolved this trait to accommodate our growing brain, which since the age of the Neanderthals has been larger than the brains of earlier human ancestors.
The Taung Child was uncovered 90 years ago in South Africa and some researchers thought the skull showed the first signs of such skull adaptation in a hominid known as Australopithecus africanus, which lived 2.1-3.3 million years ago.
For the latest study, researchers at the University of the Witwatersrand, Columbia University and Florida Atlantic University used high-resolution computed tomography to look at each layer of the skull.
"According to the authors, the results as well as comparisons with the hominin fossil record and chimpanzee variation do not support the hypothesis that the features evolved in A. africanus or early Homo hominins," said the study in the Proceedings of the National Academy of Sciences.
The advanced scans revealed more detail about the edges of what some scientists have believed were skull plates.
"The borders are not as sharp as one would expect" if there had been a soft spot, or anterior fontanelle, it said.
Furthermore, since the child was estimated at three to four years old, an open soft spot "would be extraordinarily rare" and the fossil was "well beyond the age" at which that would typically close, between three and nine months in modern babies.
The Taung Child has long been seen as the first and best example of early hominin brain evolution.