New 3-D images of Neanderthals seem to add to a growing body of evidence that Neanderthals were not close relatives of modern humans.

Christoph Zollikofer and Marcia Ponce de Len at the University of Zrich used fossils to construct virtual computer images of the skulls of Neanderthals and early modern humans.

The researchers say the distinctive features of the Neanderthal skull receding chin and low, sloping forehead were established by the age of two.

Early human skulls were found to look distinctly "human" by the same age.

The researchers say these findings support the idea that Neanderthals didn't interbreed with early modern humans. Instead, Neanderthals are considered to be a "sister" species to modern humans.

Disappeared like the dinosaurs

Neanderthals lived in Europe, central Asia, the near East and likely western Siberia until their mysterious demise about 30,000 years ago. The reason for their disappearance has been the subject of much debate and speculation.

Some believe they were killed off by humans taking over their hunting grounds during the middle of the last Ice Age. Others think they disappeared through interbreeding with early humans.

But recent DNA analysis of three Neanderthal skeletons suggests they weren't our ancestors but a sidebranch of human evolution.