A fossilised skull of the earliest giant panda has been discovered and reveals that two million years ago the animal was a pygmy.

It is the first skull of the extinct species to be found and provides a clear idea of what the ancient creature would have looked like.

It dates back at least two million years and the remains show that, at 3ft (1m) long, it was little more than half the size of the modern giant panda, which is 5ft long.

Apart from size, however, it was much the same as the modern species anatomically. The structure of the teeth shows that it had already developed a taste for bamboo.

The skull of Ailuropoda microta, meaning pygmy giant panda, was discovered in a cave in Leye, southeast China, and it has helped scientists from China and the United States to draw up the giant panda's family tree.

Analysis of the jaws revealed that by two million years ago giant pandas had developed the tough teeth required to cope with bamboo. "The premolars and molars are robust, broad crushing platforms, much as in the living giant panda," the researchers reported in the journal Proceedings of the National Academy of Sciences.

Russell Ciochon, Professor of Anthropology at the University of Iowa in the US and one of the researchers, said: "Pandas are unique bears - the only bear species that is known to exist wholly on a vegetarian diet."